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Depth of Field Muddle, muddle, muddle.......
Posted By: PenPusher, 11-26-2015, 09:32 AM

I'm looking at the Depth of Field Tables for Takumar screw mount lenses in Keppler's "The Pentax Way" from around 1970.

I am assuming that the same figures apply approximately to K, M, A, F and FA lenses as they are all 35mm full frame lenses, spot on accuracy does not matter so as long as they are in the same field it's OK.

The muddle I'm getting into starts when I'm trying to translate these figures for these lenses when used on APS-C cameras.

I initially assumed that say, the figures for 35mm lenses could be swapped for those for 50mm as the crop factor being 1.5x makes a 35mm lens 52mm which is near enough.

Then I started thinking that can't be correct and I've been going round in ever decreasing circles ever since.

Any help would be appreciated.

CD
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11-26-2015, 10:35 AM   #2
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The depth of field is unchanged at any given distance for any given aperture with any given lens. This is an optical property of the lens.

What is changing is the field of view. To keep the figures round, a 100mm lens on crop has the FIELD OF VIEW of a 150mm lens on full frame. The depth of field only changes when you alter (i.e. increase) your distance to the subject in such a way as to reproduce the field of view you would get if viewing through a full-frame system. Then the distance is greater so the depth of field increases (provided you keep the same aperture setting).
11-26-2015, 10:49 AM   #3
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It is not straight forward and the values you see in tables depend on which standard for determining the DoF (i.e. diameter of the "circle of confusion") was used.

With the value that Pentax used way back when (may differ from what Keppler used) I can calculate the following example:

Given:
Distance to subject: 5 m

I then get:

35mm lens on APS-C, F4: Hyper focal distance: 14.2m, DoF from 3.7 to 7.7 meters

52mm lens on 35mm FF format, F5.6: Hyper focal distance: 14.6 m, DoF from 3.7 to 7.6 meters

So that's how you can use the tables: Find the equivalent focal length, then compensate by one F-stop.

Hope this helps a little.
11-26-2015, 10:53 AM - 1 Like   #4
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THis might be of some use: Online Depth of Field Calculator

11-26-2015, 02:20 PM   #5
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QuoteOriginally posted by jatrax Quote
THis might be of some use: Online Depth of Field Calculator
Or from the same site, one can use:
Depth of Field Table
11-27-2015, 01:13 AM   #6
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QuoteOriginally posted by Alex645 Quote
Or from the same site, one can use:
Depth of Field Table
Thank you all, very much appreciated.

CD
03-31-2019, 03:30 AM   #7
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Found this app on Google play, may be of help: Hyperfocal Pro.HyperFocal Pro - Apps on Google Play
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04-01-2019, 04:39 AM   #8
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QuoteOriginally posted by PenPusher Quote
I'm looking at the Depth of Field Tables for Takumar screw mount lenses in Keppler's "The Pentax Way" from around 1970.

I am assuming that the same figures apply approximately to K, M, A, F and FA lenses as they are all 35mm full frame lenses, spot on accuracy does not matter so as long as they are in the same field it's OK.

The muddle I'm getting into starts when I'm trying to translate these figures for these lenses when used on APS-C cameras.

I initially assumed that say, the figures for 35mm lenses could be swapped for those for 50mm as the crop factor being 1.5x makes a 35mm lens 52mm which is near enough.

Then I started thinking that can't be correct and I've been going round in ever decreasing circles ever since.

Any help would be appreciated.

CD
You need to understand the concept from the film ero of "Acceptably Sharp". This concept applied equally to not only depth of field, but also image blurr from camera shake.

As the predominant print size was 8" X 10" acceptably sharp was determined to be when a point or line measured less than 1/100 of an inch, when a full frame exposure was blown up to 8" X 10". Nothing more, nothing less.

So given that for the same enlargement ratio was used for a crop sensor, the limit for acceptably sharp would be 1/100 of an inch on a 5x 7 print.

If you want to enlarge further, the depth of field actually reduces, but today, when you consider most of us look at images on a 22 inch or bigger monitor, the whole concept of depth of field is somewhat, well, meaningless....

04-05-2019, 03:56 PM   #9
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I'm not sure I would say absolutely meaningless, however.

In terms of exact numbers, yes, the numbers may not mean much. But, there is value in understanding how the depth of field would relate, qualitatively across various focal lengths, subject distances, and apertures. The concept is important and is one of the primary reasons I shoot with an SLR.

Now I mostly shoot for fun, and it would drive me crazy to think too exactly about depth of field, but when I was first really trying to grasp all this information, I would use a little wheel I had (BA, before apps) to help give me an idea of depth of field (and hyperfocal distance). It got me in the ballpark, and with a dSLR I would just preview the image to confirm I wasn't too narrow if it mattered. Of course, that's on a 3-in screen, so it is always a grain of salt, but now I rarely bother. I can get in the ballpark on instinct, but it hardly diminishes the value of knowing.
04-09-2019, 05:02 AM   #10
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QuoteOriginally posted by emalvick Quote
I'm not sure I would say absolutely meaningless, however.

In terms of exact numbers, yes, the numbers may not mean much. But, there is value in understanding how the depth of field would relate, qualitatively across various focal lengths, subject distances, and apertures. The concept is important and is one of the primary reasons I shoot with an SLR.

Now I mostly shoot for fun, and it would drive me crazy to think too exactly about depth of field, but when I was first really trying to grasp all this information, I would use a little wheel I had (BA, before apps) to help give me an idea of depth of field (and hyperfocal distance). It got me in the ballpark, and with a dSLR I would just preview the image to confirm I wasn't too narrow if it mattered. Of course, that's on a 3-in screen, so it is always a grain of salt, but now I rarely bother. I can get in the ballpark on instinct, but it hardly diminishes the value of knowing.
just so long as you remember, even hyper focal distance is based upon the definition of acceptably sharp, and the dreaded circle of confusion, which means it too, only really exists in the mind of a 8 x 10 inch print.
04-09-2019, 05:41 AM - 2 Likes   #11
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I tend to ignore the whole issue. I know what the sharpest f stop is for each lens I use, usually ƒ5.6, so unless I'm shooting for a narrow DoF effect, I shoot the lens at it's sharpest point. Then I change that based on circumstances. You can shoot a landscape at ƒ5.6 if you're shooting off a balcony and it's 50 feet until there is anything in the foreground. The closer the desired to be in focus foreground is the more you have to stop down, until from 6 feet away with a 50mm lens you need to be at ƒ16 or ƒ22 and diffraction is seriously limiting your image quality. But I find it pretty intuitive, if you careful look at each of your results you get the hang of it pretty quick, for each lens that you use. Couple that with the shorter the focal length the wider the DoF, and you can probably handle just about everything.

QuoteQuote:
As the predominant print size was 8" X 10" acceptably sharp was determined to be when a point or line measured less than 1/100 of an inch, when a full frame exposure was blown up to 8" X 10". Nothing more, nothing less.
If you want 1/100 inch or less on digital a K-3 produces about 2700 distinct lines per inch. A print 27 inches high would fulfill that requirement. A K-1 would be about 36 inches high. My K-1 and K-3 images both look really sharp printed 16x20 on glossy paper, to the point where you can't really tell the difference. Despite what folks say, once you get over 100 lines per inch, at least in my opinion, it's overkill. It's nice if you have it, but, you aren't getting much for it.

In actual usage though, the algorithms used in upscaling images are much better than what you can do with an analogue reproduction system, where the grain just gets larger and larger. As long as you have relatively noiseless starting image, enlargement can go well beyond that and still be acceptable if the image depends on colour or shadow and light. Of the 5 elements of design, 6 principles of organizing basic compositional elements and the five favourite rules of pictorialist composition, in all 16 general guidelines, only the reproduction of texture needs to be razor sharp. The others require varying degrees of sharpness. If you aren't trying to reproduce fine detail you can get away with a lot less, and it may improve the image quality if your image if it is less. Sometimes to much detail just looks messy. And with enlargement algorithms cleaning up the jaggies and minor imperfections in the subject the enlarged image may look better than the one taken at higher resolution.

QuoteOriginally posted by Lowell Goudge Quote
just so long as you remember, even hyper focal distance is based upon the definition of acceptably sharp, and the dreaded circle of confusion, which means it too, only really exists in the mind of a 8 x 10 inch print.
On film, but a 27 inch to 36 inch print in digital for resolution. As for circles of confusion, there's no digital advantage, but you have the ability to decide from the file how big it can go and still look good. I'm usually a couple feet from my monitor so the larger circles of confusion are in part negated by the further viewing distance.

In the end, the bottom line is ƒ5.6 or 8 is preferable for DoF with ƒ11 being acceptable when really wide is needed, and sometimes ƒ16, even with the diffraction looks better than the others. Of my bracketed exposures maybe a couple ƒ22 images have been the best choice, after between 200 and 300 thousand images over the last 10 years.

When shooting for narrow DoF, printing bigger is going to enlarge those circles of confusion, and the blurry background should look smoother as you enlarge the image (as long as you were shooting with the DFA*50 1.4 and not a lens that produces messy bokeh) , but you do have to pay attention to your 100 lw/ph minimum in the subject if there is texture, although I suspect you can get away with 70 lw/ph if there isn't, which means there will be many images where the upper limit of a K-1 file will be 50 inches, and I have a Monet like fall colours reflections K-3 image that looks great printed to 42 inches. It doesn't depend on resolution for it's effectiveness and I could probably print it at any size I wanted.

The reason DoF is such a muddle is different styles of image create different DoF requirements. It's not one size fits all.

Last edited by normhead; 04-09-2019 at 07:18 AM.
04-09-2019, 06:21 AM   #12
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QuoteOriginally posted by normhead Quote
I tend to ignore the whole issue. ........ It's not one size fits all.
i think the first and last sentence says it all.
04-09-2019, 06:34 AM   #13
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QuoteOriginally posted by Lowell Goudge Quote
i think the first and last sentence says it all.
Ya, if you're short of time, just read those two, read the rest if you want to know why i think that way.
04-09-2019, 08:18 AM   #14
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QuoteOriginally posted by Lowell Goudge Quote
just so long as you remember, even hyper focal distance is based upon the definition of acceptably sharp, and the dreaded circle of confusion, which means it too, only really exists in the mind of a 8 x 10 inch print.
Of course.... it would be silly to not recognize that link up.

The only thing I would argue is whether even an 8 x 10 means much. All our eyes are different, and what is acceptable to you in an 8 x 10 may not be to another. In other words, it is really only in the mind if one person (or perhaps a few people) who looked at some 8 x 10's and agreed.

My point was that the numbers don't mean much because it's subjective. Heck, it's not like I go out with a tape measure anyway. Normhead was hitting a similar nail as I was getting at. If I know I want a narrow depth of field, I go off of my experience and the broad concepts. I don't find it reasonable (and I am sure many of us don't) to worry about the CoC and so forth. I don't even think that hard about exactly where my lenses are sharpest. I was only noting that there was a time I concentrated (perhaps too much) on these concepts because how else can one get to the "ignore the whole issue or don't worry about it", i.e. instinctual without understanding it at some point. The true understanding comes from recognizing the imperfection of the math.

I know most my lenses are sharpest over a range of f5.6 to f8 (maybe a little broader). Of course that, like the 8 x 10 and doF, is subjective (perhaps more forgiving). These days, as a father of a 3 year old and an engineer that works 60+ hours per week, I don't worry about remember anything too specifically. I rarely get to use a tripod except to shoot the family portrait, and I rarely get to ponder over or perfect a shot. When I suspect those subjective issues might come up, I shoot a bracket quickly and move on.

If I am out shooting, it is with the 3 year old, and while she can appreciate a nice view, by necessity, my patience to get the shot can only be about as much as a 3 year old's. Later in life, it will probably hard to adjust back to trying to perfect shots. But, I will say the digital world has given a lot of wiggle room at little cost compared to the film days.

I am not old enough to have the experience of some on this forum. Film for me was something I only had the experience from perhaps when I was 10 (when I was given an SLR) through college (when I moved to a P&S digital camera). Through those ages, money is quite restrictive. I had two lenses a 50 mm and an 85 mm and perhaps enough money to buy one or two rolls of film per month. I shot a scene with one, maybe two shots. I looked at dof charts and always narrowed the aperture a half step down to guarantee I wasn't off. A landscape shot almost always took 5+ minutes of planning, and I never had a good tripod nor the ability to change iso from shot to shot. I also never shot anything more than iso 400. The patience of a 3 year old would have been futile in those days.

-Erik
04-09-2019, 08:45 AM   #15
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The simple fact is, the same settings with ISO adjusted to give you a reasonable shutter speed will give you close to optimum results 90% of the time. Messing around estimating the effect of depth of field, long exposures etc. is for the last 10%. And for many, we can live without that 10% (so for us 90% is 100%, just to be totally confusing,)most of the time. It's only for images that are really special that I shoot other than ƒ5.6 APS-c or ƒ8 on FF, a shutter speed over 1/100 and the lowest ISO possible to give me that.

That's especially true when you consider DoF changes with the crop. Unless you know exactly what size the crop is going to be, the DoF is meaningless. If you crop a K-1 image to K-5 size, now your DoF has increased a stop. You now have the DoF the lens shot on APS-c. Your ƒ8 image is now the DOF of an FF ƒ11 image.

IMHO a DoF guide that doesn't know what the final crop factor will be meaningless. What's the point of trying to be that precise when in most circumstances the result will be imprecise no matter what you do? Just another reason why knowing the characteristics of each individual lens is the most important thing and DoF calculations are way down the list. The DoF guide only gives you the DoF before cropping and may have little to do with the final image.

Last edited by normhead; 04-09-2019 at 06:39 PM.
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