Depth of Field, Hyperfocal Distance, Infinity, and Beyond! (Podcast 732)

Depth of Field, Hyperfocal Distance, Infinity, and Beyond! (Podcast 732)


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Today we’re going to look at both Depth of Field and his cousin Hyperfocal Distance, and take this to Infinity and Beyond in one post. I’ve covered Depth of Field and Hyperfocal Distance a number of times in different posts, but an update that I just completed for my iOS app Photographer’s Friend introduces a new concept related to Infinity, so I figured I’ll pull all of this into one post that will hopefully be all you need to reference to get a good understanding of these theories. We’ll start with the basics, and then geek out a little with some of the calculations, and then move on to some examples to illustrate why keeping your eye on your depth of field is important.

What is Depth of Field?

Let’s start with an explanation of Depth of Field, which is the area of a photograph that is in focus at any given setting. The depth of field is affected by a number of factors. On your camera, the setting that affects Depth of Field the most is your aperture. Wide apertures like ƒ/2.8 or ƒ/4 have a shallow depth of field, where not much is in focus, and smaller apertures, like ƒ/16 and ƒ/22, have very deep depth of field with a lot of the image in focus.

The other main parameters that affect the depth of field are your focal length and focus distance. Wide focal lengths like 24mm have more depth of field and longer focal lengths like 100mm have less depth of field, so the more you zoom, the shallower your depth of field gets. And the closer you focus, the shallower your depth of field gets as well. Let’s note too that when using smaller apertures at close range, in general, depth of field extends on third towards your camera from the point at which you are focused, and two-thirds back. The far focus limit extends out more as you approach hyperfocal distance, but we’ll talk about that shortly. For example, say you focus a 50mm lens with the aperture set to ƒ/8 at 18 feet or 5.5 meters, the near limit of the focus would be at 11 feet or 3.4 meters, and the far limit of the focus would be at 29 feet or 9 meters. So approximately one-third in front of your subject and two-thirds behind.

Depth of Field Near and Far Limits
Depth of Field Near and Far Limits

Keep in mind that the focus doesn’t just switch abruptly from being sharp to not being sharp. The point at which you focus your lens is the sharpest image that your lens and camera can resolve, and the image gets gradually softer as you move away from this point. The depth of field is the area that we would consider acceptably sharp, and it is a gradual defocussing of the image to the point where we would consider it no longer acceptably sharp, and these are the near and far limits of the depth of field.

Long-time followers might recall the following six diagrams showing the mechanism of depth of field at different focal lengths and focus distances. It’s important to understand the relationship between aperture, focal length, and focus distance before we go on, so while trying not to go into too much detail, let’s outline what I’ve covered in these diagrams. Diagram #1 shows the depth of field with a 50mm lens with the aperture set at ƒ/2.8 and focussed at 2 meters or 6.6 feet. Because the aperture is wide at ƒ/2.8 the light is focussed at a more acute angle, between the two widest points of the aperture. This means that the circle made by the light as it passes through the aperture reaches a point where it is no longer acceptably sharp quite quickly. You can see that the near limit is just 1.9 meters or 6.2 feet and the far limit is 2.1 meters or 7 feet. The total depth of field is just 27 cm or just under one foot.

In Diagram #2 we stop the aperture down to ƒ/5.6 at the same distance and the depth of field increases to 54 cm or 1.8 feet. This is just because the angle of the light passing through the aperture is now less acute. In Diagram #3 with an aperture of ƒ/11 the depth of field increases to 1.14 meters or 3.8 feet at the same focus distance, once again, because the light is passing through a smaller aperture and therefore the circle of acceptable sharpness is reached much further away from the point at which the lens was focussed. All three of these diagrams were assuming a 50mm lens focussed at 2 meters or 6.6 feet.

In Diagram #4 we take the same 50mm lens and this time focus it at 5 meters or 16.4 feet with an aperture of ƒ/5.6 and we now get a depth of field of 3.8 meters or 12.5 feet so by increasing the focus distance from 2 to 5 meters or 6.6 to 16.4 feet our depth of field is almost eight times deeper at the same aperture. Again, this is because focussing further away gives us a shallower angle of the light, so the circles of acceptable focus are further away from each other.

Conversely, in Diagram #5 we focus closer to the lens, still with an aperture of ƒ/5.6 and see that the angle of the light is much more acute and the acceptable focus circles are close together, giving us a depth of field of just 3cm or just over an inch. And the final diagram shows the angle being more acute still as the light passes through a wider aperture of ƒ/2.8 for just 2cm or 3/4 of an inch depth of field. If any part of this was new to you, I hope it’s relatively easy to understand how depth of field is affected by the aperture and focus distance. I’ll share a formula shortly that will help you to understand the relationship with the focal length as well, but before that, let’s talk about Hyperfocal Distance.

Hyperfocal Distance

For any given focal length and aperture combination, there is a point at which the far limit of the depth of field is so far away that everything after the near limit of your depth of field can be considered acceptably sharp, and this is what’s known as the Hyperfocal Distance. Here is a diagram that I created to illustrate this back in 2013, although you may see this stolen and illegally rebranded on other sites, and you can see that for a 24 mm lens at an aperture of ƒ/16 the hyperfocal distance is much closer than with a 50 mm lens, and much closer still than a lens set to a focal length of 200 mm.

Hyperfocal Distance Diagram
Hyperfocal Distance Diagram

You’ll see that I’ve added a note which reads: Although still a good reference point, note that the calculations on this diagram are based on the somewhat outdated traditional depth of field calculations which assume the photograph has been printed at 8 x 10 inches and is being viewed at arm’s length. I’ll explain more about why this might be something you need to be concerned about shortly, but these numbers are still a good standard to help talk about the theory, and before we jump further down the rabbit hole, there is another part to all of this that we’ve already touched on but need to cover the terminology first, and that is the Circle of Confusion.

The Circle of Confusion

Until now I’ve been calling it the circle of acceptable focus, to avoid ‘confusion’ but in optical physics, it’s known as the Circle of Confusion. In terms of focus, this is the limit that the light rays can spread out but still appear to be in focus. In this diagram from a post an older post, you can see that I have included light from the near and far focus limits, and tried to show how it gets gradually more blurry as we move away from the critical focus point, which is light coming from the point at which we focussed the lens.

Circle of Confusion Diagram
Circle of Confusion Diagram

The reason that the Circle of Confusion is important to this topic is that it is required to calculate Hyperfocal Distance. The calculation is actually not very difficult, so let’s go over that quickly before we move on. First here is the formula with words rather than numbers. So we have Focal Length to the power of two over the Aperture multiplied by the Circle of Confusion. This gives us the Hyperfocal Distance.

\frac {focal\hspace{2mm}length^{2}} {aperture \hspace{2mm} \times \hspace{2mm} Circle\hspace{2mm}of\hspace{2mm}Confusion} = {hyperfocal \hspace{1mm} distance}

If we replace the words with some real numbers now, we’d do, for example, 24 to the power of two over 16 multiplied by 0.030, which gives us 1200. This is 1.2 meters, which is the distance I had in my earlier diagram for hyperfocal distance. This assumes a circle of confusion of 0.030 millimeters or 30 µm (microns or micrometers) which is a commonly used circle of confusion for 35mm sensors.

\frac {24^{2}} {16\times0.030} = {1200}

So, this brings us up to speed on the theory behind Hyperfocal Distance and Depth of Field is calculated from the Hyperfocal Distance, but it’s considerably more complicated, so we won’t go into that much detail today, as the main reason for the inaccuracy of the traditional calculation is the circle of confusion, which we are now up to speed on,

Why is the Traditional Depth of Field Calculation Outdated?

As I mentioned, the traditional Depth of Field calculation based on evaluating sharpness in an 8 x 10 inch print at arm’s length, is outdated because unfortunately, more than 99% of images that are created today are never printed, so it’s really only useful as a standard to discuss the theory. Most people check focus on the computer screen, and most of the time, we check by zooming in to 100% at a point where it is important for the image to be in focus. It’s fashionable to dismiss this kind of evaluation as being too picky, but in the dark corners of our studies, hotel rooms, or basements, I know that people do this. It’s human nature to want the best for our creations, so before we really commit to liking a shot, we have to know that it’s sharp and will bear up to a certain level of scrutiny. Seriously though, if, for example, you are going to print your work out large or display it on a big screen, you have to check that it is sharp unless you did not intend it to be.

Pixel Peeper Mode

This is why I developed Pixel Peeper Mode for the Depth of Field calculator in my Photographer’s Friend app. When you enable Pixel Peeper mode we calculate the pixel pitch of your sensor based on the sensor format that you select on the main calculator screen and the number of megapixels that you select on the settings screen. I’ve outlined both of these here for anyone that uses Photographer’s Friend. I’ve included two more screenshots to the right though, to illustrate this point and to help with understanding this concept.

Pixel Peeper Mode Examples
Pixel Peeper Mode ExamplesI

The screenshot on the left shows both the Pixel Peeper Mode switch being turned on, and that I have selected the megapixels for my camera, which is the 45 megapixel Canon EOS R5. You will, of course, select whatever the megapixel count is for your own camera. Then on the main calculator screen, select your camera’s sensor format, which in my case is 35mm full-frame. If you use a crop factor camera select the correct ratio, such as CF1.6, 1.5, or 1.3, etc. The larger crop factors are actually for sub-medium format sensors and there are also sizes for medium and some large format sensor and film sizes to choose from.

The important thing with regards to depth of field here though can be seen on the two screenshots on the right side. Notice how the Hyperfocal Distance and the Hyperfocal Depth of Field readouts change when we have Pixel Peeper Mode turned on compared to when it’s off. The Hyperfocal Distance changes from 1.26 meters to 3.3 meters, which is 4.15 to 10.9 feet. Under the Hyperfocal DoF section, you can see that with Pixel Peeper mode turned off, we’re looking at the depth of field starting at 63 cm or 2 feet and extending out to infinity, which we will also talk about shortly. With Pixel Peeper Mode turned on, that increases significantly to 5.5 feet or 1.65 meters.

You may be wondering why the non-Pixel Peeper mode number is not 1.2 meters, as we saw in earlier calculations. This is because even without Pixel Peeper mode I am using a slightly smaller circle of confusion, rounded to 29 µm, as this is more accurate than 30 µm used before, and that gives us slightly longer distances. Notice though that when Pixel Peeper is turned on, the CoC label above the Format dial now shows 11 µm for the Circle of Confusion, which is much smaller. This is calculated from the sensor size and the megapixels, which enables me to calculate the Pixel Pitch, which in turn enables me to calculate the Circle of Confusion.

Airy Disk Pattern
Airy Disk Pattern

The Airy Pattern

There is actually another somewhat obscure piece to the overall puzzle that we should touch on to really make this post cover everything you need to know about depth of field, and that is the Airy Pattern or Airy Disk. With the understanding that we get greater depth of field as we make our aperture smaller, you’d think that when you want more of your scene to be sharper, you could just select a really small aperture. Many lenses for 35mm format cameras go down to f/22 and sometimes f/32 or smaller, and medium and large format lenses often go to much smaller apertures to get enough depth of field. 

But, as good as the manufacturers make our lenses, there is a phenomenon that occurs as light passes through a very small aperture that causes problems. As light passes through a wide aperture, it makes its way to the sensor or film relatively undisturbed, but as light passes through a small aperture, it interferes with other rays of light, causing it to spread out. The result is what’s known as diffraction and to explain that, we need to talk about the  “Airy Pattern” (right) with a central “Airy Disk”, both named after George Airy, the person who discovered this phenomenon.

Airy Patterns
Airy Patterns

As you can see from the mockup of the Airy Disk on the right, there is a central core of light which makes up about 84% of the light, and then a number of concentric rings. While there is still a gap between the central core or Airy Disk, and the next Airy Disk, the light is said to be “well resolved”. According to the Rayleigh Criterion, the dots are “just resolved” if the center of the first Airy Pattern is superimposed on the first dark ring of the second pattern. When two airy disks become closer than half their width, the light is considered not resolved. This is when you will see diffraction cause everything in your image to be slightly out of focus at small apertures.

Color-Coded Diffraction Warnings

Based on this and the information I already calculated in Photographer’s Friend, I am able to calculate the Diffraction Limits and this is what enables me to provide Color-Coded Diffraction Warnings. The AD label which shows the size of the Airy Disk and the Aperture Dial are color-coded to show the risk of Diffraction as you adjust the aperture dial. If you don’t see this, turn these options on in the Depth of Field Calculator settings.

Because the Circle of Confusion size is rather large in the traditional 8 x 10-inch print calculation method, you actually need to start being concerned when the Airy Disk gets to around 80% of the size of the Circle of Confusion. So, when you are not in Pixel Peeper mode, the color of the Aperture dial will change from green to amber when the Airy Disk passes 80% of the default Circle of Confusion size, and for 35mm format, that is around an aperture of f/18. It then goes red from 100%, which is f/22 at the default settings. This matches my own test results.

In Pixel Peeper mode, these boundaries are a little more conservative, but I set amber to kick in when the Airy Disk reaches the same size as the Circle of Confusion and then the red Diffraction Limit warning when the Airy Disk is twice the size of the Circle of Confusion. These parameters cause the dial to go amber from f/10 for a 35mm format camera at 30 megapixels, and then turn red from f/20. 

Based on my own tests, I personally think that f/10 is a little too early, but the physics tells us that there is a possibility of seeing the effects of diffraction at this point, so that’s what we use, but consider this as intended, as an amber warning. Ideally, you’ll do your own tests to see when you start to see diffraction in your images and adjust your expectations accordingly. There are details of how to do diffraction tests in Episode 594, when I originally talked about this.

Diffraction Warnings
Diffraction Warnings

Infinity and Beyond!

As I mentioned earlier, I’m about to release an update to Photographer’s Friend which adds a number of new features, including translation into a number of new languages and some improvements to the user interface, but the relevance for this discussion comes in the form of a new Infinity slider on the Depth of Field Calculator Settings page. Because of the work involved in bringing you these features this slider is part of the Pro Add-on, which means you need to buy the Pro Add-on for this to be available, but if you already own the Pro Add-on, you’re good to go. What this slider does is allows you to set a custom distance for Infinity. You might initially think, well, infinity is infinity, why would I need to set it? But there are a few reasons why this might be useful, as I’ll explain.

Lens Infinity and Focus Infinity

I’m risking going down a rabbit hole by bringing this up at this point, as this took a lot of wrapping my own head around initially, but I think to ultimately avoid confusion, we should probably talk about the difference between the Infinity symbol that you see on your lenses and infinity in the context of the extent of focus in Depth of Field, because these are really not the same.

If you check your lenses you will see that what is considered Infinity looks slightly different, depending on the lens. For example, when I focus with my RF 15-35mm lens from Canon, in the viewfinder I see distance guides in meters which reads 0.28, 0.4, 0.6, 1, then the Infinity symbol, which, if you follow the spacing of the marked distances, seems to signify about 5 meters. My RF 50mm lens shows distances of 0.4, 0.5, 0.7, 1, 1.5, 3, then the infinity symbol, which in this case seems to signify around 10 meters. Finally, as a reference, my RF 100-500mm lens reads 0.9, 1.2, 1.6, 2, 3, 7, then the infinity symbol, and from my tests, focus stops increasing at around 40m.

When I initially developed this feature I added the ability to restrict Hyperfocal distance down to as little as 5 meters, or 16 feet, but I found it to be almost completely useless in this context. The reason for that is because the speed at which focus advances towards infinity is non-linear. After my 50 mm lens passes 3 meters when turning the focus ring at the same rate the speed at which focus moves towards infinity starts to increase much more rapidly. Although a quarter of a turn on the focus ring might take me from 1.5 to 3 meters, the following quarter-turn doesn’t take the lens from 3 meters to 4.5 meters. Rather, it takes the lens on a much steeper curve from 3 meters all the way to infinity, and that is really far!

Non-Linear Focus Curve
Non-Linear Focus Curve

As I researched these changes I found an old forum post where people were laying down the law about infinity by lens, some quoting infinity as being as close as 20 feet, but this assumes a linear increase in the focus and an abrupt stop after the last number of the focus dial or as in the case of my Canon mirrorless camera, the focus range displayed in the electronic viewfinder, as it’s no longer present on the barrel of the lenses. Another observation is that you can actually see the infinity calculations start to peak if you opt to display the calculated Infinity value that I’ll talk about in a moment. It was watching this peek that brought all of this home to me, and that is the reason that I’ve changed this functionality in Photographer’s Friend, because I know I’m not the only geek using it. I get excited when technology helps me to gain a deeper understanding of the world around me, and I wanted to share that.

No More Limits!

Until now, when displaying Infinity in Photographer’s Friend I have simply used 1000 meters as a generic cut-off, and although we showed the infinity symbol for the depth of field, as the distance went past 1000 meters we just showed greater than “>1000 m” and that doesn’t provide the information that feeds my curiosity. So from version 3.7 of Photographer’s Friend which should be available in the App Store in the coming days, whether you own the Pro Add-on or not, you will be able to tap the Depth of Field label or the Far Limit label and cycle through three different infinity display modes.

The default mode displays the preset infinity value in parentheses, which will remain at 1000 meters and display as “>∞ (1 km)” or “>∞ (0.6 mi)”. With the Pro Add-on, the distance will change to whatever you set it to with the Infinity slider on the settings page. The second mode will just show the greater than symbol and infinity symbol “>∞” when the distance is greater than infinity. This really just gives you the option to clean up the interface, making it less cluttered when necessary. The third mode is the geeky one, which shows the calculated distance as it races towards infinity, which actually can extend out way past the originally used 1000 meter limit, so for long focal lengths, you may see something like “>∞ 57 km” or “>∞ 36 mi”. The calculated distances increase very rapidly for wide-angle lenses, so it’s harder to see the gradual increase because of the distance steps, but if you change to a longer focal length like 500mm, you can actually watch the focus increase faster and faster as it heads towards infinity, and I personally find that fascinating.

Once we hit true infinity, the depth of field calculation actually returns a negative number, so I have to convert that to a large positive number, so at that point, I have no choice but to show an Infinity symbol as we really are at infinity.

By adjusting the preset Infinity value with the new slider in the Depth of Field Calculator settings, you are giving yourself more reference points as you shoot. Because of the non-linear nature of the focus advance towards infinity, I don’t recommend trying to use something like 20 feet or a really close number that you might find online, but I have made the slider start at 50 meters or 164 feet, which I feel is close enough to be useful, and it extends out to one mile or just over 1600 meters. You use this to get a reminder of when a wider angle lens is theoretically approaching infinity, because the readout labels for Far Limit and Depth of Field will change color, and you can select any three of the modes I discussed earlier, whichever you find most useful. Personally, I’m enjoying seeing the colored label and infinity symbol kick in, but I’m working mostly with mode three, which shows the actually calculated infinity distance, so you get the best of both worlds.

For example, in this screenshot, I have Infinity set to 100m which will put you at 330 feet if you hit the new measurement unit toggle switch that I also just added, or tap the distance dial label. The focus distance is set to 75 meters, which not greater than the calculated Hyperfocal Distance, but because I have the Infinity slider set to 100m I already have a colored label for the Far Limit and the greater than Infinity symbols in place because the far limit is passed the Infinity distance that I have preset, but I have an approximately equal symbol with the infinity symbol in the Depth of Field readout, to tell me that I’ve surpassed by preset Infinity distance, but it’s not yet greater than the calculated infinity distance. Basically, we can now use this as an indication that we’re approaching the calculated Infinity, and we can still monitor that we’re not quite at true infinity because of the approximation symbol.

Approximately Infinite
Approximately Infinite

Or, for example, here I have the focus distance dial past the Hyperfocal Distance and the Infinity display in mode 2, so I just get the greater than infinity symbols for a nice clean readout if that’s all I care about. How you use these features is completely up to you. I’m just providing the tools, and as is often the case with Photographer’s Friend, some uses are practical field techniques, and others are to help you get your head around the technical aspects of photography.

Infinity Symbols Hyperfocal Distance
Infinity Symbols Hyperfocal Distance

Why is Pixel Peeper Mode Important?

A young Himba lady caught in a moment of thought
A young Himba lady caught in a moment of thought

OK, so as we start to wrap this up, I’d like to talk a little about why it’s important to use Pixel Peeper Mode. In the past, I’ve spoken with people that had concerns about focus, and sometimes think there may have been a problem with their camera. Most of the time it turns out that the problems stemmed from a lack of information or full understanding of just how shallow depth of field gets with modern high-resolution cameras. Keep in mind that if you are going to check the focus in your images by making an 8 x 10-inch print and look at it at arm’s length, the traditional calculation is fine, but for larger prints and when checking your focus at 100%, especially on a large screen, your images won’t show as much depth of field as you would think based on the traditional calculations.

To illustrate this point though, take a look at this portrait of a young Himba girl from my Complete Namibia Tour. For this portrait, I used an aperture of ƒ/2.8 which will give us a reasonably shallow depth of field, although the lens would go as wide as ƒ/1.2. It’s tempting to shoot portraits wide open, and at times I do, but you have to understand just how shallow the depth of field is. With the traditional calculation, f/2.8 at a focal length of 50mm, and I see from my EXIF data that I was focussed at 65cm, learn that I have a depth of field of 2.5 cm or one inch. That’s already quite shallow, but if I switch to Pixel Peeper mode, which calculates the actual depth of field for my 30 megapixels Canon EOS R at these settings, I find that I actually only have a depth of field of 1.172 cm which is slightly under a half of an inch.

Now, I like this look and it was intentional, but if you study the image you’ll see that only her right eye, mouth, and part of her headdress are crisply sharp. Everything else gradually gets softer as we move away from this shallow plane of focus, of just over 1 centimeter.

One person that I spoke to in the past said that they couldn’t get a sharp photograph with the Canon EOS 5Ds R, and they were shooting with an 85mm ƒ/1.2 lens wide open at a distance of around 5 feet or 1.5 meters, and they thought they should have a few centimeters of depth of field. With the traditional calculation at these settings, indeed, they would have just over 2 centimeters of depth of field, similar to what I had in this shot of the Himba girl. What they actually had was 7 mm, and when we inspected the images we could see that there was a very thin line of sharpness, rather than the image being completely out of focus as they’d thought.

This is why it is important, especially when working with very shallow depth of field, to understand just how much focus you can expect, and Pixel Peeper mode in my iOS app can provide you with this information simply by turning it on and selecting your sensor’s megapixels. If you don’t already own Photographer’s Friend, you can find it on the Apple App Store here, and there are more details about the Depth of Field and other calculators and features on the product page here.

Stopping Down for Wildlife

Another thing that comes up in conversation a lot is the necessity to stop down your aperture a little for large wildlife subjects. Sure, if you just want the eyes sharp, and yes, that can provide a beautiful look, then staying wide open is fine, but if, for example, you are photographing a large bird in flight, and want to see more of the wings sharp, stopping down a little is important. For example, this Steller’s Sea Eagle shot at 16 meters or 52 feet has a wingspan of around 2.5 meters, just over 8 feet. Even with the wings folded slightly like this, we’re still talking about almost 2 meters from tip to tip. At ƒ/10 with a focal length of 400mm, my depth of field with the traditional calculation is 90 cm or just under 3 feet, but with a 30-megapixel camera, we’re actually looking at less than half that, at 42 cm or 16 inches. Now, I don’t mind the wing tips being out of focus like this, but the amount you see in this photo is based on my selected aperture of ƒ/10. If I’d shot this wide open, there would have been much less focus on the near edge of the wings, and it probably would have bugged the hell out of me.

For this Crane shot, when there were two subjects, I was focussing at a distance of 35 meters or 110 feet, with a focal length of 700mm, and with the traditional calculation I should have around 1.5 meters or almost 5 feet of depth of field, which would probably have been enough to get both birds sharp, but for a 30-megapixel camera, which is what I was using, in Pixel Peeper mode, I see that I actually only had 68 cm or 26 inches. The result is that the second of the two Red-Crowned Cranes is slightly out of focus, even at ƒ/11. I actually often stop down to ƒ/14 when there are multiple subjects, but didn’t on this occasion, and the results are, to me at least, a little bit disappointing.

Hyperfocal Distance Use in Landscape Photography

Finally, I’d like to mention that when doing landscape photography I actually rarely photograph using Hyperfocal distance. The theory is that if you identify the Hyperfocal distance and then focus at that point, you can ensure that everything from the near limit of your depth of field to infinity will be in focus. With relatively wide-angle lenses though, the depth of field is deep enough that in general, if you focus around a third of the way into the frame, you will be approximately shooting at the Hyperfocal distance, and don’t really need to calculate it. I generally still just focus on the subject that is most important in the frame and from experience I generally know that this is going to give me sufficient depth of field. It’s important to note though that I built that experience by using tools like my Photographer’s Friend Depth of Field Calculator and checking the results of my work to ensure that my understanding of the limitations we face is accurate.

Landmannalaugar
Landmannalaugar

In this image of me looking out across the valley at Landmannalaugar in Iceland, I simply focussed on the rock on which I intended to stand, and everything from the foreground to the distant mountains is in focus because I had a focal length of 38mm and my aperture set to ƒ/16. I had focussed around 10 meters into the frame and the hyperfocal distance is around 8 meters, so everything from 4 meters to infinity was in focus.

When you use longer focal lengths, even for landscape, the depth of field does need to be considered more carefully, so I will sometimes reach for my calculator when using long focal lengths, even for landscape. I love that my Canon mirrorless cameras also now have a distance scale right there in the viewfinder so that I can see the distance at which I’m focusing when I do want to use Hyperfocal distance for maximum depth of field.

Just so that you know, it’s actually not a simple task to find the actual focus distance of an image just by looking at the EXIF data in your computer’s file browser, as few programs actually show this. I use a neat piece of software called RawDigger for this, which allows me to see what Canon interprets as the Near and Far focus limits, and that allows me to approximate my focus distance, so I just wanted to give that mention.

Out of Chicago Live!

I do hope you found this post useful. We’ll wrap it up there, but before we finish I’d like to mention that I will be teaching alongside the world’s best photographers at Out of Chicago LIVE! This will be running from April 9 to 11th, 2021, so SAVE THE DATE! You can find more information at www.outofchicago.com. I hope to see you there!

Out of Chicago LIVE! 2021
Out of Chicago LIVE! 2021

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Show Notes

See details of the Out of Chicago LIVE event here: https://www.outofchicago.com

And you can find RawDigger here: https://www.rawdigger.com

Music by Martin Bailey


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Circle of Confusion, the Airy Disk and Diffraction (Podcast 594)

Circle of Confusion, the Airy Disk and Diffraction (Podcast 594)

Today I’m going to explain what causes diffraction as we stop down the aperture in our lenses past a certain point, and how this may affect our photographs.

I’ve been working on an update to our iOS app Photographer’s Friend so that you’ll be able to do two new things. The first is to enable a Pixel Peeper mode, and the second is to display your Diffraction Limit as you stop down your aperture. I’m trying to pull this in as I prepare to leave for Morocco in a few days, so I don’t know how much I’ll be able to do, but as I looked into the calculations required to add these new features, I learned a few extra things that I’m going to share today.

Traditional Depth of Field Calculation

First let me explain that traditionally, depth of field calculations have been based on sharpness perceived in an 8 x 10-inch print viewed at a distance of 25 cm. This is what Photographer’s Friend is based on in the standard mode. This calculation is most commonly used and is fine for print and probably also for viewing your images on a reasonable size computer display. In the digital age though, with the ability to examine our images at 100%, you’d probably notice that some areas that were supposed to be sharp according to the traditional calculation may appear a little soft. Enter the new Pixel Peeper mode.

I have to admit, I’m a pixel peeper, and I’m proud of it. I love my images to be tack sharp where intended, and therefore, I do check critical focus at 100% during my editing and selection process, before I decide if an image is worthy of keeping or not. So, I’ll probably be using Photographer’s Friend in Pixel Peeper mode most of the time.

Note that I’m currently not thinking it’s worth building in support for various print sizes because as the print size increases we generally move further away making the difference negligible. Of course, photographers often view prints much closer than non-photographers, checking for sharpness, but I’m pretty sure that puts you in the Pixel Peeper category, so we now have that covered.

I’ll go on to talk a little more about the app updates later, but for now, I want to talk about these three critical elements relating to sharpness in our photographs, which are Circle of Confusion, the Airy Disk and Diffraction.

The Circle of Confusion

The Circle of Confusion seems confusing in itself, but it’s really quite simple. Its size depends on the parameters you set but traditionally it is based on viewing an 8 x 10 print at 25 cm or 10 inches because it’s a fundamental part of the calculation of depth of field. I’ve created a diagram to help explain, as you can see here (below).

Circle of Confusion Diagram

Circle of Confusion Diagram

When we focus on a subject, the lens is basically, to the best of its ability, going to focus the light from that subject as sharply as possible onto our camera’s sensor or film. The point at which we focus our lens, the focal plane, will be the sharpest part of our photograph. This is known as Critical Focus. If you look at the enlarged section of my diagram you’ll see that light from this area is focussed as the smallest resolvable dot of light, represented by a red dot. If you can only see the blue and teal dots on the sensor in the diagram, click on it to view it large in your browser.

Objects that are closer or further away from our focal plane grow gradually less sharp, because the light from objects further away is focussed in front of our sensor, and light from objects closer to the camera is focussed behind our sensor. But, the light from these distances only spreads out by a certain amount, which is represented by the middle teal colored circle in my diagram. This amount of spread in the light is what’s known as the Circle of Confusion.

According to the traditional calculation, if you were to view the resulting photograph as an 8 x 10-inch print at 25 cm, you would perceive the light that has only spread to the limits of this circle to be sharp. The distance between the two points inside which the subject will be acceptably sharp is known as our Depth of Field. Anything in our photograph that is closer to the camera or further away, past these two limits are considered outside the Depth of Field and will therefore no longer be acceptably sharp when viewed in that 8 x 10 print.

Circle of Confusion Calculation

If you are wondering what actual size the circle of confusion for the traditional calculation is, for a 35 mm original image enlarged to 25 cm (10 inches), the length of the 8 x 10-inch print, you’d be multiplying the image by seven. If we consider that the smallest resolution we can determine with regular eyesight is 0.2mm, we would divide that by 7 giving us 0.029 mm or 29 μm (micrometers). This is what I use for the 35 mm format calculation when not using the new Pixel Peeper mode.

Custom Circle of Confusion Setting

You will see slight variations on the size of the circle of confusion, as there are a number of ways to think about this. Rather than trying to cater for all possibilities programmatically, if you prefer to use a different circle of confusion to that which I’ve set as the default for each camera format, from v2.3 you will be able to enter a custom size under the advanced settings page, that we’ll look at shortly.

So, to quickly summarize what we’ve covered so far; subjects at our focus distance or focal plane will have their light focussed to on the sensor in an even smaller circle than the circle of confusion, so subjects on the focal plane will be the sharpest area of our photograph. Subjects any closer or further away from that area of critical focus will grow gradually less sharp until the light from them spreads to the size of Circle of Confusion. At this point, they are on the limit of acceptable focus, or in other words on the very edges of our depth of field. Light from anything any closer or further away from these limits will spread to a size large than the circle of confusion, and so will appear to be blurry and get blurrier the further from the depth of field they get as their circle of confusion continues to grow.

At this point, they are on the limit of acceptable focus, or in other words on the very edges of our depth of field. Light from anything any closer or further away from these limits will spread to a size large than the circle of confusion, and so will appear to be blurry and get blurrier the further from the depth of field they get as their circle of confusion continues to grow.

Pixel Peeper Mode

As I mentioned earlier, there are times when we want sharper images than those required to create a sharp print at 8 x 10 inches. In my mind, the best test is when we can view an image at 100% on our computer screen, and still see that all of the areas that we intended to be in focus, are indeed in focus.

My answer to this dilemma is the new Pixel Peeper mode that will be introduced in V2.3 of Photographer’s Friend that I hope to release soon. Basically what this provides is a way to calculate the Circle of Confusion automatically from your sensor size, which you select via the Format dial in our Depth of Field calculator, and the megapixel dial that you’ll find under the new Settings screen, that you can see in this screenshot (below).

Pixel Peeper Mode

Pixel Peeper Mode

I’m still working on this update, so nothing is set in stone at this point, but as you can see, there will be a new line of buttons and displays between the settings dials and the Depth of Field readouts, and the Settings button is on the right. At the bottom of the Advanced Settings screen, is a switch to turn on Pixel Peeper mode, and a dial to select your camera’s megapixels.

The addition of these settings enables me to calculate a new Circle of Confusion, that you can see above the Format dial, and I am also now calculating the Pixel Pitch which is the second display from the right. The Circle of Confusion is basically the pixel pitch multiplied by 2.5, which will give good sharpness even when viewed at 100%.

Diffraction Limit Color Coding

The other important thing that this enables me to do is to calculate the size of the Airy Disk, which I’ll explain shortly, and that gives us information on when your image may start to suffer from Diffraction. As you can see from the screenshot, the AD or Airy Disk display and the Aperture dial are both colored green. This is because I’ve turned on the top two new options to change these colors to indicate how I’m doing with regards to Diffraction.

As you can see in these next screenshots (below) as you select smaller apertures, the dial and readout changes to amber to so indicate that there is a danger of being Diffraction Limited and then red to tell you that you pretty much are now going to be Diffraction Limited.

Diffraction Limit Color Coding

Diffraction Limit Color Coding

You can select to display either of these color coding options separately or none at all if you don’t care. But, diffraction is a real issue and something that we need to keep in mind if we want sharp photographs. Let me explain why.

The Airy Pattern

Airy Pattern

Airy Pattern

With the understanding that we get greater Depth of FIeld as we make our aperture smaller, you’d think that when you want more of your scene to be sharper, you could just select a really small aperture. Many lenses for 35mm format cameras go down to f/22 or sometimes f/32 or smaller, and medium and large format lenses often go to much smaller apertures to get enough depth of field.

But, as good as the manufacturers make our lenses, there is a problem that occurs as light passes through a very small aperture. If you picture water coming out of a hose, unrestricted the water comes out clear, relatively undisturbed, and at pretty much the same diameter as the hose and then starts to gradually spread out. If you attach a device to enable you to create a smaller hole though, the water becomes disturbed and starts to spread out much more quickly.

Well, that same thing happens with light. As light passes through a wide aperture, it pretty much just makes it’s way to the sensor or film, but as light passes through a small aperture, it interferes with other rays of light, causing it to spread out. The result is what’s known as the  “Airy Pattern” (right) with a central “Airy Disk”, both named after George Airy, the person who discovered this phenomenon.

As you can see, there is a central core of light which makes up about 84% of the light, and then a number of concentric rings. While there is still a gap between the central core or Airy Disk, and the next Airy Disk, the light is said to be “well resolved”. According to the Rayleigh Criterion, the dots are “just resolved” if the center of the first Airy Pattern is superimposed on the first dark ring of the second pattern. I’ve tried to express this in the below mockup.

Airy Disk Patterns

Airy Disk Patterns

Another way of putting this, according to the Cambridge in Colour website, is that there is an impact on the image once two airy disks become closer than half their width.

I referenced a great Cambridge in Colour article on Diffraction Limited Photography as I consolidated my thinking on this, and they state that “an Airy disk can have a diameter of about 2-3 pixels before diffraction limits resolution”. It was this and a few other points that made me realize I could calculate the Diffraction Limit programmatically by adding a few other parameters to my DoF calculator.

The key point to keep in mind here is that the Airy Disk grows as the aperture gets smaller, causing the light to spread out, and there’s an easy formula to calculate this. I then figured out how to calculate the pixel pitch based on the size of each sensor format and with the megapixels input through the new dial on the settings page, I can calculate and compare the size of the Circle of Confusion for the evaluation of sharpness at 100% screen viewing.

Color-Coded Diffraction Warnings

Because the Circle of Confusion size is rather large in the traditional 8 x 10-inch print calculation method, experience tells me that you actually need to start being concerned when the Airy Disk gets to around 80% of the size of the Circle of Confusion.

So, when you are not in Pixel Peeper mode, the color of the Aperture dial will change from green to amber when the Airy Disk passes 80% of the default Circle of Confusion size, and for 35mm format, that is around an aperture of f/18. It then goes red from 100%, which is f/22 at the default settings. This matches my own tests perfectly.

In Pixel Peeper mode, these boundaries are a little more conservative, but at this point, I’m setting amber to kick in at around 100% and then the red Diffraction Limit warning from around 200%. Because of the size of the Circle of Confusion at this high resolution, these parameters will cause the dial to go amber from f/10 for a 35mm format camera at 30 megapixels, and then turn red from f/20.

Now, I personally think that f/10 is way too early, but the physics tells us that there is a possibility of seeing the affects of Diffraction at this point, so I want to keep it in, although it’s only as the amber warning.

Test For Yourself

Of course, how much diffraction you actually see in your images will depend on your camera and the quality of your lenses. The warnings that we’ll display in Photographer’s Friend are intended as a guide only. The best course of action would actually be for you to do a simple diffraction test with your own gear. You can point your camera at pretty much any scene for this, but I like to place a steel rule on a surface, and set my camera up on a tripod, then, using a 2-second timer or cable release so as not to move the camera during the exposure, shoot a series of images, starting at say f/5.6, then f/8, and from say f/11 onwards, shoot a frame for every step you can stop down your aperture.

When I did this test with my Canon EF 24-105mm f/4 IS Mark II lens, I found that the only noticeable degradation due to diffraction was between f/20 and f/22. It’s barely noticeable, but here are the two frames at 100% in which you can see the difference. You’ll need to open up your browser window and click on one, then move back and forth with your mouse or keyboard arrow keys to see any difference.

My 24-105mm lens only stops down to f/22, so I also checked with my 100-400mm lens, which stops down to f/40 when the focal length is set to 400mm. Here is a set of images from that test, starting at f/11 down to f/40. I had image stabilization turned on, because of the long focal length, and the possibility of my house shuddering from train movement etc. so the image moves slightly between some of the frames, but the lack of sharpness as you stop down is due to diffraction.

The first noticeable drop in sharpness due to diffraction is again at f/22, so it seems that the Canon 5Ds R with no anti-aliasing filter is not affected by diffraction until f/22, at least with the two lenses I’ve tested. This is good news, as I have habitually been keeping my aperture to around f/14 or sometimes f/16 to avoid diffraction because that’s where it started with my 5D Mark III. I’ll keep the possibility of going a little further in mind as I shoot moving forward, and also be sure to test new cameras before shooting with them in future. You’ll also notice that by f/40 the images are really soft, all down to diffraction.

You might also be wondering if the closeness of my test subject may affect the results, but I did a series of shots out of my studio window and the results were the same. Diffraction kicked in at f/22. Do take a moment to test your own lenses though, and let me know your findings in the comments to this blog post. This will help me to fine-tune the parameters for the new Diffraction Limit color-coding. Include your camera format, i.e. 35mm, micro four-thirds, and the megapixels, as well as when you saw the effects of diffraction kick in etc.

New DoF and HyperFocal Distance Values

The other thing to keep in mind is that the Depth of Field and Hyperfocal Distance also change when you use Pixel Peeper mode. This update is not just about Diffraction. This means that as you check the depth of field and hyperfocal distance values, you will notice that you need to stop down your aperture a little more to get enough depth of field to keep everything sharp if that’s your intention.

For example, in the standard mode, with a full frame 35 mm sensor and your aperture set to f/8 and a focal length of 50 mm, when focusing at 3 meters, you’ll get a depth of field of 1.78m and the hyperfocal distance is 10.83 m. In Pixel Peeper mode using a 30-megapixel camera with the same settings as before, you’ll only have 77 cm depth of field, and your hyperfocal distance changes to 23.3 m. This is as expected because you are working with a smaller circle of confusion for a sharper image.

For our metrically challenged friends, the same settings, f/8 at 50 mm, focusing at 9.8 feet, you’ll have a depth of field of 5.77 feet and a hyperfocal distance of 35.5 feet in the normal mode. In Pixel Peeper mode, again with a 30-megapixel camera, you’ll get a 2.5-foot depth of field and your hyperfocal distance becomes 76.58 feet.

I’m actually expecting that with camera’s and lenses being so good these days, it’s this feature that may ultimately be more useful than the Diffraction Limit warnings, but I still think it’s useful to have this information, so that we can make the right decisions as we shoot, to create the best quality images possible.

Related Content

Before we finish, I wanted to let you know that if you are not aware of how the aperture setting and subject distance affects the depth of field, I posted a pretty thorough article in episode 132, have an article here. I also released a post on Hyperfocal Distance in episode 437.

So, I hope this has helped to understand the Circle of Confusion, Diffraction Limit, and the Airy Disk. These are subjects that I’ve found myself living in over the last week as I’ve worked on this update for Photographer’s Friend, so I figured it was as good a time as any to put my thoughts down in words here.

Note that I’m leaving for Morocco in a few days, and because I’ve been busy with this update and other preparations, I haven’t been able to prepare any additional episodes for release while I’m away, so there won’t be any new episodes until the middle of November now.

Also note that as I build out the functionality of the app, I think it’s fair to increase the price from the introductory $2.99 to $3.99 when I release version 2.3, so if you are thinking of picking up Photographer’s Friend, save yourself a dollar by buying before v2.3 is released. If I can get enough testing done over the next couple of days, I’ll release before I leave for Morocco, but otherwise, it will be mid-November. And of course, if you miss that, it’s still going to be only $3.99, probably until I add a third calculator or some other significant new features.

Download Photographer's Friend from Appstore


Show Notes

The Diffraction Limited Photography article on Cambridge in Colour: http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

Get Photographer’s Friend on the App Store here: https://mbp.ac/pf

Music by Martin Bailey


Audio

Subscribe in iTunes for Enhanced Podcasts delivered automatically to your computer.

Download this Podcast in MP3 format (Audio Only).

Download this Podcast in Enhanced Podcast M4A format. This requires Apple iTunes or Quicktime to view/listen.


Understanding Hyperfocal Distance (Podcast 437)

Understanding Hyperfocal Distance (Podcast 437)

I was thinking about hyperfocal distance recently, and wondered how long ago it was that I did my original podcast on this subject. I checked this morning, it was almost eight years ago now, so I decided to cover this subject again today. Much of what I said back then holds true of course, but I also recalled making a diagram last year that really helps to understand hyperfocal distance, so we’ll take a look at that as well today.

Although I love to use shallow depth-of-field, with the foreground and background out of focus, often for landscape work it’s nice to get everything in focus. This is what’s known as pan-focus, and can be achieved by setting your focus to what’s called the hyperfocal distance, as I’ll explain.

Avoid Diffraction

It’s tempting of course to just stop your aperture down as far as it will go, and try to increase your depth-of-field so much that you think everything will be in focus, but that’s not really the case. Diffraction will get in the way. Diffraction is what happens to light when it travels through a small hole. As the light comes out the other side, it spreads out, and the result is that if you stop your lens aperture down too much, the entire image starts to get soft and slightly out of focus. This, of course, defeats the object of stopping down to make everything sharp.

The aperture from which you will start to see diffraction kick in varies from lens to lens, but generally, it will start from around f/16, and by f/22 really start to become a problem. If you are a Canon shooter and need to remove diffraction from an image, there is a tool in Canon’s Digital Photo Professional called the Digital Lens Optimizer. As much as I dislike Digital Photo Professional, this can be a very powerful tool if you simply must stop down to f/16 and beyond to achieve the depth-of-field necessary for your image.

The Digital Lens Optimizer basically takes all of the information available from the computer design processes as Canon develops their lenses, and reverse engineers things like diffraction and chromatic aberration, basically realigning the image data to form a much cleaner image. As an example, here is a closeup of the bottom right-hand corner of a photo that I shot at f/16, but at f/16 my 16-35mm lens starts to get a little soft from diffraction and suffers a little from chromatic aberration in the corners.

Click on the images to view larger, but you can see that once the Digital Lens Optimizer is applied (below), it sharpens up a lot, almost completely removing the affects of diffraction, and the chromatic aberration that I circled in the left image disappears.

Before Using Canon Digital Lens Optimizer

Before Using Canon Digital Lens Optimizer

After Using Canon Digital Lens Optimizer

After Using Canon Digital Lens Optimizer

You can remove chromatic aberration in Lightroom’s Lens Corrections panel too, but the ability to remove the affects of diffraction when you have to stop down to a small aperture is worth noting if you’re a Canon user. In reality, I dislike Digital Photo Professional so much, that I rarely use this tool, but it can save you if you absolutely must stop down to f/16 and below, to achieve pan focus, even when you are focussing at the hyperfocal distance, which I’ll explain now.

Sharp Shooter Cover

Hyperfocal Distance

There are exceptions to the guidelines I’m about to explain, based on focal length and how close you are focusing, but in general, when you focus your lens on something a reasonable distance from the camera, the depth-of-field, which is the area of the scene that will be in focus, extends approximately one third in front of the point at which you focus your lens, towards the camera. It also extends approximately two thirds into the scene, away from the camera, after the point at which you focussed your lens.

Depth-of-field is of course affected by the focal length of your lens, and the distance to the subject as well as your aperture. Basically the longer the focal length, the shallower the depth-of-field, and the more difficult it becomes to achieve pan-focus. Here’s the diagram that I used to explain this in my Sharp Shooter ebook from Craft & Vision. (Click the diagram to view larger.)

Hyperfocal Distance Diagram

Hyperfocal Distance Diagram

Let’s walk through the examples given. For example if we shoot with a 50mm lens at f/16, the hyperfocal distance is just over 17 feet (5m). That means that if we focus at 17 feet, the depth-of-field, or the area of the image that will be acceptably sharp starts at 8.6 feet (2.6m) and extends to infinity. Some lenses have a distance scale on them in a small window, which you can reference to set an approximate focus distance.

If you use a wider focal length though, such as 24mm, again at f/16, the hyper-focal distance is just 4 feet (1.2m) from the lens, and if we focus at this point, everything from 2 feet (0.6m) to infinity will be in focus. This is literally right in front of the lens, so you can see how much more depth-of-field you can get with wide-angle lenses.

Conversely of course, this means that long telephoto lenses are not really suited for shooting using the hyperfocal distance. As we see in the diagram, at 200mm with an aperture of f/16, the hyper-focal distance is 274 feet (83m) with acceptable focus starting at 137 feet (42m), which is obviously not going to cut it if we want the foreground to be sharp.

Of course, you might not be shooting at f/16, and as I said, I generally try not to stop down below f/14, which I consider my soft ceiling, and f/16 is pretty much my hard ceiling for aperture settings. I only use a smaller aperture than that when I really have to, such as to achieve a longer shutter speed. I never go smaller than f/16 for depth-of-field, unless I commit myself to using Canon’s Digital Lens Optimizer.

Stone Jetty

Stone Jetty

For example, for this photo (above) shot in Okinawa a couple of years ago, because I was shooting at 50mm, I needed to stop down to f/22 to get everything in focus from three or four feet out to infinity. If I recall, I bit the bullet, and made a mental note to clean this up with the Digital Lens Optimizer later, and it worked out pretty good. As I’ve mentioned before, most rules are really just guidelines. The trick is knowing what tools you have in your toolbox and using the right ones at the right time.

Calculating Hyperfocal Distance

OK, so we’re going to geek out a little bit here, as I explain how to calculate the hyperfocal distance. Don’t worry though. You don’t need to remember this. There are calculators for that, but let’s just walk through this to be thorough.

So, to calculate hyperfocal distance we have to first know the size of the circle of confusion, and this is often based on an image being printed out at 8×10 and viewed from 2 to 3 feet. Confused? OK, so the Circle of Confusion is basically the smallest recognizable dot that a lens can create. This is literally the tiniest little dot that can be created when the lens is perfectly focussed.

Once the focus shifts in front or behind the dot, or if diffraction kicks in, the dot starts to spread out and become blurred. What this means is for an image to be in focus, the light cannot spread out any more than the size of the circle of confusion. Once that happens, it appears blurred. This is also how we get that beautiful bokeh in our images.

So, how big is the circle of confusion for a DSLR camera? Well, for a 35mm full frame camera, it’s generally 0.03mm, and for crop factor cameras is generally around 0.02mm. You can probably find your camera in the list over at the Dofmaster web site where they have a great online hyperfocal distance calculator.

OK, so here’s the really geeky bit. Once you know the size of your circle of confusion, to calculate the hyperfocal distance, you divide the focal length to the power of two, by the aperture, multiplied by the diameter of the circle of confusion.

Let’s say we’re going to be shooting at 35mm, 35 to the power of two is 1,225. If we are working with a circle of confusion of 0.03mm, and an aperture of f/16, we need to multiply 16 by 0.03, which gives us 0.48. Then divide 1,225 by 0.48 to get 2,552. As this is currently millimeters, if we divide that by 1000 we get 2.552 meters, or 8.37 feet, which is the hyper-focal distance.

Now, if you intend to print out your images larger than 8 x 10 which is used to calculate the circle of confusion, you would actually need to calculate your hyper-focal distances differently, but as a general guide these calculations are fine, and this is what most hyperfocal distance and depth-of-field calculators use as a base.

On that, I know this is going to sound like a blatant plug, but when I’m out in the field, and need to calculate hyperfocal distance, I generally use the calculator built into the MBP iPhone app. I need to get a few things updated in the app, but the depth-of-field and hyperfocal distance calculator are the easiest to use and understand that I’ve used. You literally just have to select your camera, focal length and aperture, then tap the Hyperfocal Distance panel in the bottom left of the screen, and the Subject panel will show you the hyperfocal distance. It’s as easy as that.

Hyperfocal Distance Rule of Thumb

Although I use my app in the field quite often, and it’s great to learn about hyperfocal distance, once you have an idea of how your lenses work at various focal lengths, you don’t have to get the calculator out every time you want to shoot at the hyperfocal distance.

For wider focal lengths, I often just stop the lens down to between f/11 and f/14 and focus about a third of the way into the scene. For very wide-angle lenses I literally just focus on the foreground, and this is usually enough to give me good depth-of-field in my images.

Of course, even when we use a calculator and get the exact distance to focus on for pan focus, you aren’t going to pace out the distance and focus exactly at that point. I do use the scale on the barrel of the lens for the lenses I own that have this scale, but many zoom lenses don’t even have this, so you have to just estimate roughly how far into the scene you need to focus anyway.

As I said though, I do try to avoid stopping my lenses down past f/16 to avoid diffraction when possible. It seems counter intuitive, but although stopping down to say f/22 will give you a deeper depth-of-field, the entire image gets a little softer, so you defeat the object of stopping down. At the end of the day though, the effect is not that great, and can be removed anyway if you’re a Canon shooter, so if you really need to stop down, it’s not such a big deal.

I hope this has helped some. I do tend not to talk about some of these photography techniques because I’ve already covered them, but I know that there are a lot of new listeners that subscribe all the time, and don’t necessarily go back to through the archives, so I’ll cover some areas like this again in the future.

Note though that we have covered many, many areas of photography over the years, and we have avery powerful search function on the blog too, and now that all episodes ever released are all on the blog, you can easily find topics that I’ve covered that you might not be aware of, by going to any blog page, and searching with the search field at the top of the sidebar. As you type a list of posts in which I mention your keyword will display and be refined as you continue to type. Give it a try the next time you’re trying to find information on something.

The Podcast is 9 Years Old Today!

Before we finish, I’d like to give myself a pat on the back, and thank you all for continuing to listen to this Podcast. I realized as I was sitting down to record this episode, that it was exactly nine years ago today, September 1, 2005, when I released episode one of the Martin Bailey Photography Podcast. I’ll stick some candles in a cup cake or something later, but I thought I’d mention this before we wrap up for today.

As you can see from the episode number, I’ve missed a few weeks here and there, usually when traveling with my tours, and through a spot of illness a few years ago, but in general, I’ve been able to create an episode every week for these nine years, and I reckon that’s a bit of an achievement. I know that many of you have listened from episode one too, which is another incredible achievement, so thank you!


Show Notes

Pick up my Sharp Shooter eBook from Craft & Vision: https://mbp.ac/cvss

The MBP iPhone App with DoF Calculator: https://mbp.ac/app

Dofmaster Hyperfocal Distance Calculator: http://dofmaster.com/dofjs.html

Music by Martin Bailey


Audio

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Download this Podcast in MP3 format (Audio Only).

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Yachiho Highlands – Part #2 (Podcast 142)

Yachiho Highlands – Part #2 (Podcast 142)

Following on from last week, today we continue to trace my steps from a recent trip to the Yachiho Highlands as I share some of the images I brought back with me, intermingling tips on decisions I made while photographing the area. As I mentioned last week, some of the focus of this series is on achieving a lot of depth-of-field, something that I don’t do a lot in much of my work, but for landscapes and the sort of photography I did during these few days it’s pretty important. If you didn’t listen to last week’s episode, number 141, I suggest you go back to that one first before listening to this, just so that you can get an idea of where we are and what I did at the end of the first day out here.

The weather forecast for this weekend had been rain on Saturday, but clear on Sunday, which is one of the reasons why I came out here. The rain on the Saturday was going to give me some nice mist which we saw last week, but also, a nice blue sky can be nice sometimes, as we’ll see in a moment. We got up at the crack of dawn on Sunday the 1st of June, and heading back up the road towards where we’d photographed at the end of the first day. As we climbed the mountain, we stopped a couple of times to take in the fresh air and just have a look around. As I mentioned last week, part of the reason for this trip was just to really get away from Tokyo with my significant other, and just relax. The mountain air was as sweet as ever, and as we stood at the same place that I’d shot the landscape shots that we looked at at the end of episode 141, we could see all of the houses and everything in the valley that had been covered with cloud the previous day, looking more like a lake than a valley. I shot a few images on the way up, but as the sun rose, even though it had only just risen above the horizon, it was very strong, and didn’t make for much of a shot. I wanted to get back to the place that I’d shot the previous day before the sun got too high in the sky, so bearing in mind that we had to stop to take in the mountain air from time to time, I was also trying not to spend too much time getting up here.

As I turned off onto the smaller road that took us down to where the Rhododendron that I’d photographed the previous day was, almost immediately we saw a long line of cars parked at the side of the road. I’ve seen this before, and on a Sunday morning in the mountains, it could mean only one thing. There was something to photograph nearby. I pulled over to see what it was, and grabbed my camera, and headed along the line of cars. There was a small picket fence along the side of the road, but as I looked through the gaps, I could see a large group of photographer’s gathered around the Rhododendron tree that we can see in image number 1804. I’m not sure, but it was likely that this is the same tree that I’d seen in a magazine, and that had been the reason for my visit in May 2007. As I said last week, I’d never found it last year, despite looking through this fence as I drove around the area, because I’d come a few weeks too early. The late snows had held back the flowers, and because we’d had snow in April this year too, I came a few weeks later, and got here at just about the best time. I walked through the fence and waited a little while for someone to move, so that I can get my camera in for this shot, but wasn’t all that happy about shooting something that not only everyone else was shooting, but from a position that I really couldn’t choose myself. I wanted to get a shot of the bush framed by the white birch, which is why I waited here, for a space to free up, but it would have taken a long time to wait for a number of spaces to free up to get some other angles, and I was still hoping to get down to the tree that I’d shot the previous day, so I didn’t hang around here. I shot this with my 70-200mm F2.8 lens at 70mm with an exposure of 1/6 of a second at F11, with ISO 100.

Rhododendron in White Birch

Rhododendron in White Birch

I dropped back though, allowing a patient pensioner to jump into the spot that I’d been in for a few minutes, and I got back into my car and drove down the hill a way. In image number 1805, you can see that I’d made my way back to the hillside with the bush that I’d photographed the previous day. There was a beautiful blue sky, with some nice wispy clouds blowing across, and it was really just a wonderful morning. It was just coming up to 7AM when I shot this one, so the sun had started to climb pretty high in the sky right now. The Rhododendron was in shade still though, which I was fine with. I shot this with my 16-35mm F2.8 lens, at 19mm, again with F11 for 1/10 of a second at ISO 100. As I mentioned last week, with a wide angle lens like this the hyperfocal distance is just a few meters from the lens, even with relatively wide apertures, but I decided to stop down a little more to get things really sharp from the closest grasses to the further trees and leaves that are visible in the shot. I hadn’t focused on the hyper-focal distance, as there really wasn’t anything so close the front of the shot that warranted it, and with F11, I knew I was going to be OK again. I considered using my 24mm Tilt Shift lens here too, to correct the trapezoidal effect a little, which is that leaning inwards of the tall objects that we see with wide angle lenses. I wanted to go a little wider than that though, and although I could have stepped back a little, other trees would have started to get in the way, and I was not too worried about leaning in of the trees either, so I decided not to spend the time to set up a shot with the tilt shift lens.

Birch, Azalea & Blue Sky

Birch, Azalea & Blue Sky

I wanted to also mention that I used my Singh-Ray ColorCombo™ filter for this shot, which basically combines an LB Warming Polarizer and LB Color intensifier in the one filter! It’s a beautiful filter, and one that although I’ve owned for more than six months now, have really not had a chance to use that much until now. The LB in the names stands for Lighter and Brighter, because these filters are literally lighter and brighter than their predecessors, by as much as one full stop. I can’t find a reference to this on the Singh-Ray web site right now, but I believe this filter is rated at just 2/3 of a stop, so it really doesn’t darken things down very much at all, although it does give a great polarizing effect as well as warming up the colors in the scene at the same time. Be warned though if this filter pricks your interest, because they are not cheap. The 82mm thin frame version that I bought for my 16-35mm F2.8 lens, which is the second version, with an 82mm filter thread, costs $450, which is about 3 times more than even the best polarizer that I can get in this size here in Japan. For the extra light though, and image quality, I think it’s worth it. It’s a beautiful filter.

Before we move to the next image, I want you to quickly note how bent the tree is in the left of the frame here. There are four trees growing almost from the same spot, but the one on the left here is not bending inwards from the trapezoidal effect than the other three here. Keep that in mind, and now let’s look at image number 1806. Here we see three trees that appear to be growing almost straight up, but in actually fact they are all growing outwards slightly, including the one on the left, which is growing out at quite an angle. This is working against the effect of the wide angle lens looking up at the tree though, so it all has basically straightened itself out, which I thought was pretty cool. For this shot, to emphasize the feel of the height of the trees, I set my camera on my tripod at its lowest height, with none of the leg extensions extended. I used my angle finder to look down into the camera from above, so that I didn’t have to lie down on the still wet and very thorny forest floor. I used an aperture of F11 for 1/15 of a second, at ISO 200 this time. I was using ISO 200 because I had turned on the Highlight Priority feature of the 1Ds, because as you can see there was shadow on some part of the bark of the white birch trees, but some parts was fully little by the sun, and I wanted to keep as much detail in the bright areas as possible. I was shooting at 16mm for maximum looking up at tall objects effect. Again, the Singh-Ray Color Combo filter helped to give me a lovely blue sky, but also with nice rich greens. I angled the camera so that I could see the trees starting to spread out at the top of the frame, but I also wanted to include the line of tree that ran across the bottom of the frame in the distance, to kind of anchor the shot, giving it more balance. I’d focused on the tree trunk in front of me, which was about a meter from the camera, again, being aware that with an F11 aperture, the hyperfocal distance at 16mm is about one meter, or three feet. This allows me to focus quickly, but also know that everything from the bark of the trees at the bottom of the frame to the furthest leaves in the distance will be in focus.

White Birch & Blue Sky

White Birch & Blue Sky

Shortly after this, we decided to go back to the hotel for breakfast. I love being able to get out and photograph for a few hours from dawn, then going back to the hotel for breakfast before eight and then setting out again. It feels like you really make the most of a day when you do this. One problem that I had though was that I’d had too little sleep the few nights before coming away, and then getting up at around 4:30AM on this day too, was starting to take its toll. After a steady breakfast, as the sun was already well and truly up, and pretty harsh, I decided that I’d have another hour’s sleep before heading back out, which is exactly what I did. Feeling a little better, we set out again from the hotel at around 10:30AM, and were going to take a walk around the park that I’d visited on my own the previous year. It was a nice walk, but pretty tiring. I had actually carted my 600mm F4 and 300mm F2.8 lens among others, all around the park, up and down hill, because the previous year I’d gotten some nice bird shots here, and was hoping to be in luck again. When I got to the spot where I’d seen the birds the previous year, after a relatively long wait, it seemed that I was not going to be as lucky this year. My other half was also getting a little impatient, so trying hard to keep this a relaxing and relatively stress free weekend for my wife, we decided to move on. This meant that I’d carted my 600mm around with me for nothing, but then I can do with the exercise, so I shouldn’t grumble. We picked up some snacks at the hotel and decided to sit on a bench near a pond in the park for lunch. As we approached the pond, I saw that there was some nice fresh green leaves on the hillside that ran up from the edge of the lake, that would probably make for a nice reflection shot if the breeze would let up long enough to take the edge of the water.

I chose a bench that would make it easy for me to set up my camera waiting for the breeze to die down, and still have a relaxing sit down for lunch, kind of killing two birds with one stone. After getting the exposure right, and thinking of a few possible compositions, we ate lunch, and waited. The breeze kept up though, and for a good thirty minutes or so, it didn’t look as though my luck was in again. Then, after what I knew was probably my last, just five more minutes, the breeze died, and I was able to capture image number 1808. You can see that it is not exactly a mill-pond type reflection, but the trees on the bank have reflected nicely in the slightly agitated surface of the pond, making a kind of painterly effect. This is just what I was hoping for. I shot this with my 70-200mm F2.8 lens at 90mm, again at F11. F11 seams to almost be a theme that ran through this long weekend. There’s actually a good reason for that, especially with the 70-200mm, which I’ll get to in a short while, when we look at the next picture. Anyway, on the composition of this shot. I basically as you can see have cut off all traces of the hillside itself, relying totally on its reflection to make up the image. At the very top of the shot though, I’ve included what look like some dead tree stumps, which were jutting out of the water. This gives us something in the shot to focus on that is totally sharp, and they also have their own reflections in the water, so we can see where at least some of the reflections are coming from. I shot a vertical and horizontal version of this and uploaded both to my online gallery at martinbaileyphotography.com. We won’t look at both of them today though, as they are very similar, but if you want to check it out, there’ll be a link in the show-notes to view all 31 images that I upload from this long weekend.

Early Summer Reflections #1

Early Summer Reflections #1

After getting the shot next to the pond, we started to climb up out of the valley that the longest track through this park takes you, and along the way kept stopping to see if we could spot any of the birds that were singing us along the trail. We saw a few, but they were too small, too far away, and too quick to really be possible to get a decent shot of, so we just kept going for the most part. I did make a quick recording of their song though, which I’ll play to you now. The sound of the water running through the park can be heard too, but take a listen to the song that accompanied us on our walk.

After our walk in the park, we decided to take a drive of about 20k to a nearby town called Tateshina. Tateshina is where many people have their weekend retreats, and quite a nice little town. It wasn’t the town that I was interested in though, it was a waterfall that basically translates as Big Waterfall, which was about a ten, fifteen minute walk from a nearby car park. Now, we’re not going to get to see the waterfall today, although the images are online if you want a sneak preview, but I wanted to look at two more images today, which are of the forest that you walk through to get to the falls. Let’s first look at image number 1810. As you walk along a path half way down the hillside, towards a river that is flowing downstream of the waterfall, there’s a wonderful forest that expands up the hillside to your right. The amazing thing about it is that all of the trees are growing over and around rocks. We can see that pretty much the whole of the forest floor is fallen rocks, covered in most, and from small gaps in the rocks, the trees are growing. They almost all seem to grow out at whatever angle they can, then start to straighten up, and head skywards. This maybe because the rocks are slowly slipping down the hill but I’m not sure.

Rock Forest #1

Rock Forest #1

Again here I use an aperture of F11, and got my camera down very low, looking up, across the rocks. I was always going to be looking up this hill, but getting down nice and low helps to emphasize the feeling of looking up and the steepness of the hill. The canopy of the trees and angle of the sun, now having much of this hillside in shadow, meant that the shutter speed for this shot needed to be 6/10 of a second, just over half a second.

Let’s look at one last shot for today, and I’ll explain that depth-of-field thing that I keep alluding to. The image is number 1811. I’ve mentioned hyperfocal distance a number of times last week and this week, and how we can use it to get what is called pan focus, which means that everything from the foreground to the furthest thing in the distance is in focus. In this shot, I focused on the trunk of that big tree in the foreground, maybe just over a meter from the camera. This again, with a focal length of 16mm, going to be roughly the hyperfocal distance. When I look at this image at 100%, I can litereally see all the hairs on the moss at the very bottom of the frame, the closest thing to the camera, and also see all the twigs and leaves on the branches of the furthest trees. All of it is in sharp focus. There is a little softness around the edges, caused more by the physics of the lens, than the depth-of-field. This second version of the 16-35mm F2.8 lens is sharper around the edges than the original version, but still gets a little soft when used wide open at 16mm. You are probably wondering why I don’t just stop down the aperture much further, to the minimum aperture for the lens, which should really sharpen things up, right? Wrong. This is the point that I have wanted to make. Some of you will have heard of diffraction. Diffraction is what happens when light passes through a substance, like the glass of a lens. The theoretical resolution of a lens is limited by diffraction.

Rock Forest #2

Rock Forest #2

There is a point with all lenses where stopping down the lenses aperture no longer makes the image sharper, and continuing to stop down past that point, actually can start to make the image more blurred. In my experience, the 70-200mm F2.8 lens from Canon does not get any sharper after F11, which is one of the reasons why I use F11 so much when I want a lot of depth of field. If the subjects you want to focus one are far enough away, sticking to F8 is more advisable, because many lenses are sharpest at F8, especially cheaper lenses. If I want a lot of depth of field though, with the 70-200mm I still rarely go past F11, though will on occasion go to F16, even though I understand that this is rarely going to make things any sharper. With the 16-35mm, I find that there is actually a little more sharpness that can be gained by going down to F16 over F11, but it is rarely necessary because wide angle lenses have much deeper depth of field, even at F8 and F11.

If you don’t believe me on this, or you want to find out what the optimal aperture is on your own lenses, find a scene with lots of detailed objects both close and in the distance, and take some test shots. Use a tool like Barnack which I’ll put a link to in the show notes, to find out what the hyperfocal distance is for the focal length you’ll shoot at, and manually focus your lens to that point and shoot away. If you are not too worried about the foreground, and just want to see how sharp things get, you can always just autofocus on the scene too. Stop down the aperture in full stops, from say F8, through F11, F16, F22, F32 and see what happens. If you want, you might want to do the full range, starting from wide open through F4, F5.6 and then on to F8 etc. I find that as you shoot with your various lenses, you do get a feel for their best apertures for optimum sharpness, but still, a little practice with them doesn’t hurt, and might save you messing something up in the field by having better knowledge of this beforehand.

So, once again, I hope you enjoyed this virtual tours in the Yachiho Highlands. We’ll continue next week, looking at a few more shots, including those waterfall shots that I was just talking about. If you’ve been by the forum in the last few days you’ll have no doubt noticed that I have updated the forum software to version 3 of phpBB. I have also changed the theme of the Web site a little moving away from the orange with some blue, to a predominantly blue theme. I’ve still got some graphics to update, but didn’t want to wait until I’d found time to complete all of the work to upgrade, as I was wasting too much time each day deleting spammers email addresses. I wanted to use some of the better administration tools with the latest version of the board, and also was hoping it would be better at keeping those unscrupulous spamming pond life at bay, and so far, it seems to be doing so. I’ve also decided to try the site without the full toolbar across the top of the forum, for two reasons. The first being because I am not sure it’s necessary. Once in the forum the navigation is pretty self contained and I have linked the new round logo at the top of the page back to the top of the Martin Bailey Photography site, so it’s always easy enough to get back. Also, I am trying to keep maintenance down. It takes a fair amount of messing around to get that toolbar into the forum theme, and that slows me down when upgrading, so if possible, I think I’d prefer to leave it out. If however you come by and think you’d really like it to be reinstated, please do let me know and I’ll think about.

Anyway, that’s it for today. You have a great week, whatever you’re doing. Bye bye.


Show Notes

Here’s a link to the Singh-Ray Color Combo filter: http://www.singh-ray.com/shop/lighter-brighter-lb-colorcombo-polarizer/

Here’s a link to Mikkel Stegmann’s Barnack utility that I reference so much for depth-of-field and hyperfocal distances, and mentioned in the Podcast: http://www.stegmann.dk/mikkel/barnack/

The music in this episode is from the PodShow Podsafe Music Network at http://music.podshow.com/


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Michael Rammell

Posted on behalf of Martin by Michael Rammell, a Wedding Photographer based in Berkshire, England. Michael also has a long-standing passion for Nature & Landscape photography. To catch up with Michael, visit his Web site, and follow him on the following social networking services.

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Q&A #3 – Understanding Hyperfocal Distance (Podcast 65)

Q&A #3 – Understanding Hyperfocal Distance (Podcast 65)

Today I’m going talk about what Hyperfocal Distance is, and how to apply it practically in our photograph, in response to a question that long term listener and moderator on the Martin Bailey Photography Forum, Marisa Firpi was kind enough to record for us using the MobaTalk Comment System that you can find on the top page at martinbaileyphotography.com.

Thanks very much for the question Marisa. It’s great to hear your voice after knowing you for so long from the forum, and this is a really great question. I’ve actually been thinking of talking about this for a while, so right now seems to be perfect timing. Firstly, here’s a quick explanation of what Hyper-focal Distance is, and then I’ll move on to a more detailed explanation of how it is calculated and how to apply it practically into our photography.

Hyper-focal Distance
The hyper-focal distance is the distance at which a particular focal length and aperture combination can be focussed at, to render everything from half of that distance to infinity in focus. This is especially useful to know about when we’re shooting landscapes for example, when we want sharp focus throughout the image, from the nearest to the further object. Here’s a couple of quick example of a focal length and aperture combinations and the resulting hyper-focal distance, before we get into the details. First, if we shoot with a 50mm lens at F16 aperture, the hyper-focal distance is 4.74m or 15.54 feet. That means if we focus on a point 15 and a half feet from our camera, everything from almost half of that distance, or just under 8 feet to infinity will be in focus. In metric that would be a hyper-focal distance of 4.74m to focus on, rendering everything from 2.37m to infinity in focus.

The wider the lens, the closer the hyper-focal distance becomes, so here’s another example. Let’s use 28mm. If we again use F16 at 28mm focal length, the hyper-focal distance is 1.5m or almost 5 feet. If we focus at this point, everything from 2.46 feet or 0.75m to infinity will be in focus. So you can see that the wider the lens, or put another way, the shorter the focal length you are shooting at, the closer the hyper-focal distance and near focus distance gets.

We should also note that telephoto lenses are not really suited to shooting using the hyper-focal distance to get subjects from the foreground to infinity in focus, as the physics make it impractical and even impossible to do this after certain focal lengths. For example, even if we go back to F16 for the aperture, but set the focal length to 200mm the hyper-focal distance becomes 75m or 247 feet. This gives us a near focus distance of 125 feet or 38m which is really not good if we want the foreground subjects in focus.

Circle of Confusion
One thing that we cannot ignore when calculating the hyper-focal distance is the Circle of Confusion. Now, a detailed explanation of the Circle of Confusion would make this week’s episode way too long, but here’s a quick explanation.

The size of the Circle of Confusion for any camera or film size or sensor size is the size of the smallest spot that will show up as just a dot with no recognisable height or width when printed on 8×10” paper and viewed from 2 to 3 feet away. So by a spot, I mean just a tiny little dot that you will not be able to make out as having any shape. If it was to get any bigger, it would start to look like a tiny circle, and that’s too big. Now of course, if you print the same image out at larger than 8×10, or view it from closer or further away, then the results will change, and this is why there is so much debate over how to accurately calculate the Circle of Confusion. Of course the spot is only attainable when sharply focussed. As soon as the focus moves to something other than the spot it becomes slightly blurred. This is what gives us the bokeh, or the out of focus areas of an image. The circle of confusion becomes larger as it moves closer to or further away from the film plane. Only parts of the image at exactly the point where the light converges being focussed on the film plane are totally sharp.

I like to think of this as the spot of a magnifying glass. If you’ve ever taken a magnifying glass outside on a sunny day and dropped a piece of paper on the ground, then concentrated the light of the magnifying glass to burn the paper, you’ll know what I mean. When you place the magnifying glass over the paper initially, the spot of light will be large and faint, but as you move it closer to the paper, the spot will become smaller and brighter, more concentrated. There’ll be a point when the spot becomes the smallest it’s going to be, and this is the point where the paper usually goes black and bursts into flames to the amazement of you and all your friends, but if you move the magnifying glass even closer, to the paper, the circle starts to get larger and fainter again. At the point at which the spot is the smallest it can be, that could be thought of as the smallest circle of confusion for that magnifying glass. Everything outside of that is just varying degrees of bokeh.

So how big is this spot on a 35mm camera? Although it varies by equipment, common sizes I’ve heard of are between 0.025 to 0.030mm, most schools of thought and many calculators use 0.030mm as the default setting for a 35mm film or full-size sensor DSLR. For digital cameras with a focal length multiplier of 1.6, 0.019mm is recommended, and for 1.5X cameras 0.020mm is recommended. There’s actually a pretty extensive table that I got these sizes from at dofmaster.com.

Calculating Hyper-focal Distance Mathematically
Remember that the size of the circle of confusion is based on an image being printed out at 8×10 and viewed from 2 to 3 feet. So it follows that if you intend to print out much larger, you would actually need to calculate your hyper-focal distances differently, but if you start going down that root you’ll probably spend more time calculating your distances than actually shooting. I’d recommend just sticking with the sizes I just mentioned or the one for your camera in the chart on DOFMaster.com for your calculations. I’ll talk in a moment about some useful tools to use as quick lookup guides in the field, but first let’s talk briefly about the actual calculation. Once you know the size of the Circle of Confusion you want to work with, to calculate the hyper focal distance, you have to divide the focal length to the power of two by the aperture multiplied by the diameter of the circle of confusion. Firstly, let’s say we’re going to be shooting at 35mm, 35 to the power of two is 1,225. If we are working with a circle of confusion of 0.030mm, and an aperture of F16, we need to multiply 16 by 0.030, which gives us 0.48. Now if divide 1,225 by 0.48 we get 2,552 and some tiny fraction below the decimal point. As this is currently millimetres, if we divide by 1000 we get 2.55 meters, or 8.37 feet, which is the hyper-focal distance.

Tools to Calculate Hyper-focal Distance
Although this is not a difficult calculation if you have a calculator with you, in the field when we’re trying to get the shot, if you are going to shoot using the hyper-focal distance, then you really want something a little easier. I have actually recently bought a new cell phone (This is outdated. I have since gotten an iPhone, and have new tools, which I mention in my Podcast and will blog about later), which is a Windows Pocket PC based PDA, so I’ve installed a piece of software from a person called Jonathan Sachs, who has kindly made a number of incredibly useful application for the Pocket PC, three of which I use a lot and would like to quickly mention are Ephemeris, which is a utility to tell you the phases of the moon, and the sun and moon rise times based on the city you select from a pull-down. This is incredibly useful, not to mention fun to play with. Another is Expose 1.0, which lists exposure guides for various light sources, and the option of applying a polarizer or ND filter to the calculation as well as changing the ISO, Aperture and Shutter speed etc. With the meters in cameras being so good these days, I don’t think I’d use this in the field, but again, it’s fun to play with. Finally, the program that is really relevant for today’s topic is DOF 1.0. As the name suggests this is a Depth of Field calculator, but it also displays the hyper-focal distance and near and far focus distances for any focal length and aperture combination. This also allows you to change the resolution, which I find is pretty much the same thing as the Circle of Confusion in this utility. The hyper-focal distance is a constant once you’ve selected your focal length, F stop but there’s also a pull-down to set the distance at which you intend to focus, and the near and far focus distances are calculated from this. Once you set the focus distance to anything equal to or further than the hyper-focal distance though, the far focus indicator changes to say “infinity”. I’ll put a link to Jonathon’s download page for these applications in the show notes too. There are other utilities that you can download from the page too, which are really very useful

Fuji & Flowers

Fuji & Flowers

One of the reasons I bought a Pocket PC based cell phone was because I wanted to use this DOF tool in the field. I used it for the first time recently when shooting Mount Fuji with some flowers in the foreground that I wanted to also get in focus. If fact, let’s take a look at the shot so that I can explain what I did. It is image number 1156. Basically, I wanted the pampas grass at the edge of the lake and as many of the flowers in the foreground in focus as possible. I don’t like to stop down less than F16 as the image starts to soften up after that, so I dialled in 50mm into the focal length field, and 16 into the F stop field. I could then see that the hyper-focal distance was just over 4 meters. This means that if I focussed on the pampas grass, which was about 5 meters from where I was standing, of course the pampas was going to be in focus, but also everything from 2.25 meters to infinity was also going to be in focus.

Another option which was raised a while back in the martinbaileyphotography.com forum, especially if you don’t have a PDA, is a card that can be printed by a piece of software available from dofmaster.com. I’ll put a link in the show notes as a reminder, but basically there are a few applications to make it easy to print out both Depth of Field charts and Hyper-focal distance charts. These can be printed on card or paper that you may want to laminate to stop it getting all messed up in your camera bag, and although I’ve not tried this myself, I’m sure they make a very easy lookup option while in the field. You can also change the various parameters like the size of the circle of confusion and the widest and smallest aperture, and the shortest and longest focal length, among others.

Of course, you’re not always going to have a subject that you want to focus on, so although I actually moved back from the scene we just looked at to get my 5 or so meters distance, and focussed on the pampas, what you can do is just use the distance legend on your lens. Most lenses have them, so you can use that to set the lens to the hyper-focal distance and forget about it for that scene. In fact, even if you can roughly guess your focusing distances, I’d suggest that you check the scale on your lens to make sure it’s accurate. And remember to switch your lens or camera to manual focus mode or when you press the shutter button it will re-focus on the scene, likely moving the focus away from the hyper-focal distance point at which you manually focussed.

I also want to briefly reiterate, because I don’t think I stressed this much earlier, that the Hyper-focal Distance is not the nearest point of the image that will be in focus. The calculation is actually a little more complicated, but basically roughly half of the Hyper-focal Distance is the near focus distance. For example if you focus on a Hyper-focal Distance of 10 meters or about 30 feet, the near focus will be half that, which is 5 meters or 15 feet. Everything from that point, out past the Hyper-focal Distance to infinity will be in focus.

Start Wrap-up: So that’s about it for today. Again, this has been quite a technical Podcast with lots of numbers and calculations to follow. Remember that I’m currently considering making Adobe Acrobat PDF transcripts of the episodes available for a nominal fee of $3.99, and there’d be discounts for 5 and 10 download credits. You would be totally in control of which episodes you bought, but I’m thinking that the transcripts for more technical episodes like this one, the Understanding MTF Charts, or exposure technique episodes for example would be more useful. I’m not going to invest time and money in creating these though if you, the listener’s don’t really want them, so I started a poll in the forum a few weeks back to gather your feedback. If you have an opinion on this, please do go to the thread and cast your vote, and also leave some feedback if you have any. Thanks very much for all the valuable feedback and votes I’ve received so far, but I’d like more opinions before I make up my mind on whether or not to invest in this venture. I’ll put a link directly to the Poll in the show notes. If you really don’t want to register in the forum and yet you want to provide feedback to me on this, or any other topic, please do drop me a line.

So, that really is it for this week. I hope you have a great week, whether you’re out shooting, or whatever you do. Bye bye.


Show Notes
Music from Music Alley: www.musicalley.com/

The software for easy printing of the DOFMaster Hyperfocal Chart can be downloaded from here: http://www.dofmaster.com/

There’s also a table at DOFMaster.com with the Circle of Confusion sizes for most digital cameras. This is necessary to calculate the Hyperfocal Distance with most tools if you don’t just go with the default for 35mm cameras, which is 0.030mm. See here: http://www.dofmaster.com/digital_coc.html

Here is where you can find Jonathan Sach’s DOF 1.0, Ephemeris 1.0 and Expose 1.0: http://home.comcast.net/~jonsachs/


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