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
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.
DOF Diagram #1
DOF Diagram #2
DOF Diagram #3
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.
DOF Diagram #4
DOF Diagram #5
DOF Diagram #6
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
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
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.
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.
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 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
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
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
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
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
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
Why is Pixel Peeper Mode Important?
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.
Cranes' Song
A Steller's Sea flying above the harbour wall in Rausu
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
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
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For this week’s episode, I’m releasing a new tutorial for our Photographer’s Friend Depth of Field calculator, and I’ve included some practical examples from the field so this may be useful as a general tutorial, even if you don’t own Photographer’s Friend.
I was actually going to just release this video in the background, but with a bunch of stuff that came up and the fact that it’s supposed to be a holiday in Japan today, I decided to make this it for this week. If you are completely uninterested in our iOS app and have no interest in Depth of Field, I have a nice meaty episode lined up for you next week, so please stay tuned.
If you are interested in the new tutorial though, I’ve embedded it below, and you can also find it on our Photographer’s Friend Tutorials page. Also, a quick shout out to listener Ron Paynter in Australia, with a thank you for pointing out that I had a typo in the Startup Help for the Exposure Shift calculator. I can’t believe I missed out the “f” in Shift, but thanks for bringing some laughter to our breakfast table yesterday morning Ron.
I was actually working on a minor update to the app anyway, so the typo has been fixed in version 3.0.4 which is already on the App Store ready for people to upgrade. Anyway, here is the video, which I hope you enjoy, and I’ll be back with another episode next week.
I’m incredibly happy and proud to tell you that our iOS app Photographer’s Friend version 3 is now available on the App Store! I was able to create an upgrade option as well, so today I’m going to fill you in on all the details.
It took me a few weeks longer than I’d hoped because I decided to add one last feature that proved to be a lot more difficult than I’d imagined, but as I knew it would be necessary, I think it was worth spending the extra time. I also really wanted to provide a way for existing Photographer’s Friend 2 owers to get a discount on the upgrade, and this took a few more steps that also delayed this announcement.
But, I am really happy to tell you that Photographer’s Friend 3 is now available in the App Store, and I was successful in setting up a mechanism to get existing customers a discount, and you don’t see that very much in the App Store. Basically what I’ve done is created a bundle, which is usually a way for companies or developers to sell additional products to customers at a discount. Our Photographer’s Friend Upgrade Bundle though does just that —provides a way to upgrade with a discount.
How it works is this. If you bought version 2 and probably also if you got version 2 as a free upgrade from version 1, you should see the words “Complete My Bundle” when you visit the bundle page. The price of the bundle is $6.99 US, but the amount that you originally paid for Photographer’s Friend is automatically deducted, resulting in a discount.
Another cool coincidence is that iOS 12 has just been released and in the Control Center we now have a button to start a native QR code reader, and I love QR codes! If you start the QR code reader and point it at the code above, you will be able to automatically just to the Upgrade Bundle on the App Store to upgrade to version 3 at a discount. If you want to upgrade of course.
If you are happy with the two calculators in version 2, you are most welcome to stick with version 2, but please note that all new features moving forward will be added to version 3. We did just release a small update to version 2 though, to make the Depth of Field calculator a little more accurate, so you aren’t being left out to dry.
There were various prices for version 1 and 2 over the years, ranging from an introductory price of $2.99 which then changed to the regular price of $3.99. If you paid $2.99 for your previous version, that is deducted from $6.99, meaning you’ll be able to upgrade for $4, a saving of 20% over the cost of version 3 which is $4.99. If you paid $3.99 for a previous version, you will be able to upgrade for $3, which is a saving of 40% off the full price.
I love this way of providing a discount because it’s completely fair in my opinion. People who paid less earlier pay more now, and people who paid more, now pay less. There’s a beautiful almost Kharma-like harmony to that!
In version 3, I’ve just posted a minor update for review by Apple with some under the hood updates, and a few more tweaks to the number of decimal places displayed in the Depth of Field calculator, making it even more useful when working with very shallow depth of field.
Introducing the Exposure Shift Calculator
The major update, of course, is the addition of a third calculator that I’ve called the Exposure Shift Calculator, rounding out the team of photography assistants in your pocket, and removing any confusion over how to change your exposure, or finding good settings from a light meter’s EV reading.
Rather than going through all of the details here though, I’ve created a video to walk you through this new calculator, which you can see below.
This video is one of three that I’ll be creating to explain each of the three calculators, and these are now linked to an Online Video Tutorial page under the Links and Help sections in the Photographer’s Friend app, so I hope you find these useful. There is still a help section for each calculator inside the app, that you can reference without an internet connection, as I know many people use the app in situations where connecting to the internet isn’t possible, due to either location or cost constraints.
Do let me know what you think of the new calculator, and once again I’d like to thank listener Steve Jarrel who provided the initial idea for the Exposure Shift Calculator, although my implementation may not be quite what he had in mind. I know from experience of talking about exposure in the field, that these exposure shifts can be confusing to calculate, so I think this will have practical uses.
Also, I think it’s great as an educational tool. There are situations when teaching photography when I wished I had a way of graphically showing how the Aperture affects the Shutter Speed, or the ISO affects the Aperture, and I can now lock any one of the three dials in the Exposure Shift Calculator and show just that, as we move any of the two dials that are not locked. And the Exposure Value lock moves all both of the free dials as you move a third, which again, is a great educational tool, and a way to find good settings changes based on EV readouts from a light meter.
Of course, just playing with the calculator is a great way to get a better understanding of how exposure settings affect each other, so I urge anyone that buys Photographer’s Friend to play away, and build a better understanding, so that you don’t struggle with this stuff in the heat of the moment in the field.
Anyway, as I say, I won’t try to explain this all in words, as the video will be much easier to understand, so please do take a look. If you don’t yet own Photographer’s Friend, but would like to buy it, you can use the QR code here to jump to the App Store or simply type in https://mbp.ac/pf3 in your browser on your iPhone or iPad, or search for Photographer’s Friend in the App Store. Do make sure that you buy version 3 though, and not version 2, unless you really don’t need the Exposure Shift calculator and want to save a dollar. If you’d like more written information before deciding if Photographer’s Friend is for you or not, the product page is here.
Apple, the Apple logo, iPhone, and iPad are trademarks of Apple Inc., registered in the U.S. and other countries and regions. App Store is a service mark of Apple Inc.
Android Version on the Way
I also wanted to say before we finish, that I am looking into a way to port the code that I have to Android, and hope to be able to bring you an Android version before too long. I know you want it, it’s just a matter of making the time now to make it happen, but I am on it.
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
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
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
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
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
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.
f/20
f/22
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.
f/11
f/13
f/14
f/16
f/18
f/20
f/22
f/25
f/29
f/32
f/36
f/40
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.
It gives me great pleasure to tell you that I have now released the update to our iPhone app, Photographer’s Friend. We now support iPad in addition to iPhone and iPod touch, as well as landscape and portrait orientations.
As I mentioned in an update a few weeks ago, from the end of August I started studying how to develop for iOS, and following a week going through an online course, I set about the task of rebuilding our old MBP Podcast Companion app, as it was a little too long in the tooth to support iOS 11, which has now been released.
I picked up the Swift programming language relatively quickly with the aid of the online training, augmented by other invaluable resources such as the Hacking with Swift and Stack Overflow websites, I was able to create the app that I’d designed in my mind, and even add a number of features that I didn’t think I’d be able to do at this point.
I submitted Photographer’s Friend for review last Thursday, and it was passed as I got up on Friday morning, and I’ve been delighted to see hundreds of updates from the previous version happening across the planet. Although I put a lot of work into this, I really wanted to make it a free update for all of the users that had been kind enough to buy the original app, so I’m also very pleased that I was able to achieve this.
Anyway, I’ve put together a video to walk you through the features of Photographer’s Friend v2.0 which I’ve embedded below. If you’d prefer to read, scroll down for a summary or visit the product page for more details.
Feature Summary
[custom_font font_family=’Open Sans’ font_size=’19’ line_height=’26’ font_style=’none’ text_align=’left’ font_weight=’500′ color=” background_color=” text_decoration=’none’ text_shadow=’no’ padding=’0px’ margin=’0px’]Photographer’s Friend is the only app on the App Store as of Oct 9, 2017, that has both a Depth of Field calculator and a Neutral Density filter calculator. [/custom_font]
I’ve gone into great detail as I implemented both of these fundamental photography calculators, and I’m very proud of how they’ve turned out. The settings of the Depth of Field calculator can all be adjusted with your thumb while holding the app in one hand because sometimes you only have one hand free.
Depth of Field Calculator
To calculate your depth of field, you just set your Camera Type, which is your film or sensor size, and choose an aperture and focal length, and set the approximate distance to your main subject. So basically everything is set with the four dials across the bottom of the interface. The two blue labels indicate that there is some functionality there. You can toggle between feet and meters by tapping the [Focus ft/m] label.
If you tap on the other blue label which displays the Hyperfocal Distance calculated from your selected settings, that Hyperfocal Distance is transferred to the Focus Distance dial, and the display is updated to show your near focus limit, the actual focus distance, and at Hyperfocal Distance, of course, the far limit is infinity, as you can see in the left of the three screenshots (below). All of these settings are saved, so even if you don’t use the default 35mm Camera Type, your selection will be restored whenever you open the app.
Photographer’s Friend DoF Calc and ND Calc
I even built in a NightView mode for the Depth of Field calculator, so if you are using the DoF Calc at night, and don’t want to lose your night vision, just shake your device to toggle in and out of NightView, which you can see in the center image (above).
Neutral Density Calculator
The Neutral Density calculator, which you can see to the right of the three screenshots (above) takes your base shutter speed and calculates the new shutter speed that you have to set after attaching Neutral Density filters to your lens to slow down your shutter speed. Simple to use, you just dial in your base shutter speed on the left and tap any of the filters on the right, and your newly calculated shutter speed is displayed at the top of the screen.
If your calculated shutter speed in 5 seconds or longer, the Timer becomes active, and we’ll sound an alarm when it finishes to let you know. The first time you start a Timer running, you will be asked for permission to send you notifications via the Notification Center, and if you grant that, if the app is closed or in the background when the timer ends, you’ll see an alert on your device instead. This works even if you force close the app or restart your device.
Links and Help
There is also a scrolling list of links to articles on Depth of Field and Neutral Density filters, as well as a link to open our podcast in the iOS Podcasts app, which now displays images again as we progress through various topics. There are contact us links and I also added some help screens to walk you through how to use the two calculators, in case some of this theory is new to you.
Anyway, that’s a quick summary for you. I do hope you’ll check out the video that I put together or have a look at the product page for more details. For the introductory price of just $2.99 for two epic photography calculators, I think Photographer’s Friend is a steal, so I hope you’ll pick up a copy, from the App Store.
Note that if you’ve updated to the latest version of iTunes on your computer, you will not be able to buy iOS apps unless you click through from an iOS device.
Please Rate and Leave a Review
If you find Photographer’s Friend useful, please do consider giving us a rating and leaving a review on the App Store. I’ve reset the reviews for version 2.0 and we need some high ratings and positive reviews to start ranking highly in searches.
