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

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Download this Podcast in MP3 format (Audio Only).

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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/


Audio

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