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

[Lowell Goudge]

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.



-Erik

The point was that the original definition was an infinitely fine point or line had a thickness of 1/100 of an inch when printed on 8x10 paper.

[normhead]

The point was that the original definition was an infinitely fine point or line had a thickness of 1/100 of an inch when printed on 8x10 paper.

And the important part of that is that 100 lw/ph will look good whatever size it's printed. You can increase the size as the camera resolution increases.

[photoptimist]

The Eagle-Eyed Pixel Peeper and the Perfunctory Print Peruser might well disagree on whether the DoF in a given image is exactly 1 meter or 2 meters. However, they can't help but agree on the overall relative sharpness effects of aperture choice. For a given sensor, focal length, cropping, and subject matter, changing the aperture of the lens changes the sharpness of the scene is nearly universal ways:

At wide-open aperture:

• the in-focus center of the image is OK but could be sharper
• most lenses show non-uniform sharpness across the frame -- the edges and corners are much softer than the center.
• the range of subject distances that are "in focus" is quite narrow.

Stopping down a bit from wide-open toward the sweet spot:

• the in-focus center of the image becomes sharper than it was wide-open
• most lenses show increasingly uniform sharpness at the in-focus distance across the frame.
• the range of subject distances that are close to the in-focus sharpness grows larger.

Stopping down more than the sweet spot:

• the in-focus center of the image becomes softer due to diffraction
• most lenses show very-uniform sharpness across the frame.
• the range of subject distances that are as sharp as the center-in-focus spot is even larger.

The point is that:

• wide open: only a narrow back-to-front slice of the center of the frame is in-focus
• sweet-spot: the center is as sharp as the lens can get, edge-to-edge is decently sharp, and some range of front-to-back is sharp
• closed-down: much of the front-to-back and corner-to-corner of the scene has uniform sharpness but that sharpness is not as good as the sweet spot sharpness

Thus, aperture choice is important if the photographer wants to either isolate the subject, have edge-to-edge uniformity of focus, or ensure that everything from some close foreground to a deep background is in focus.

As for using a DoF calculator, the calculators do work but each photographer needs to figure out their personal tolerance for the circle of confusion (CoC). That depends on the photographer's chosen format, their personal assessment methods (e.g., a print of some size vs. pixel peeping) and their personal subjective sensitivity to OOF. Once they know their CoC, they can calculate DoFs and hyperfocal settings that work for them.


(Note: "most lenses" means most lenses that are not decentered and that have decently flat fields. Decentering and field curvature can harm edge and corner sharpness even when stopped-down.)

[Tab Zee]

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.

I guess I opened a can of worms with my automatic DOF question. When I had my Brownie, I never worried about it. I was then 11 years old. Now I am 84 with poor eyesight. I used to be a more serious photographer at 50 with fairly good eyesight. I know that DOF is a multi parameter problem. I've written the equations for it (hyperfocal, normal, and macro) and could post them here if you wish. I have received lots of responses, some more or less suggesting I go back to the Brownie hyperfocal mode. But, I am looking for a critical measurement and semi-automatic at that. The best answers that I received are: a) No camera has the direct mode for it by the numbers, b) With good eyesight and critical eye evaluation, one can use the the "preview" function / image, c.) one can carry a cheat sheet in your back pocket, d.) download "Camera Calculators" app to one's smart phone......I like answer c) the best and have downloaded it. It is quite simple and one can even specify you desired Circle of Confusion, or use a standard d/1500. But what c) does could be easily implemented with auto or semi automation as a mode in the modern "smart" camera. Here's my recent example: I am shooting copies of my 35 mm slides using a modified stack loading Kodak projector, a macro lens and my K10D mounted on a tripod looking into the vacant lens opening of the projector. I have a home-made low wattage bulb replacing the 300 Watt EHL. I have disconnected the projector's servo slide positioning lamp because its light output interferes. My DOF is less than a millimeter. Now I know my focusing problem, but I had to use c) or numerically solve the equations. I have also looked at the hundreds of Sierra wildflower photos that I have on slides and wonder if I could have done better. With the in-camera DOF feature for which I am asking, it would have been a snap. Unhappily, I am no longer hiking the Sierra ...... but I am going to Costa Rica with a new KP.

[photoptimist]

....
But, I am looking for a critical measurement and semi-automatic at that.

Now that's an even harder problem! Any "critical measurement" of DoF will discover that it varies from lens to lens, from center to edge to corner, and at different distance settings. The DoF equations that those calculators use all assume that the lens is optically perfect in every respect from center to corner and at every distance setting. But actual lenses have a varying non-zero blur circle even in zone of sharpest focus. That intrinsic blur adds to the DoF blur to create a bigger blur in the final image. Thus, a low quality lens or a lens that is soft in the corners or a lens that is soft at minimum focus distances might have blur circles bigger than the CoC at all distances. Better lenses will have deeper DoFs that approach the calculated DoF. Also, diffraction at the narrowest apertures will degrade measured DoF perhaps even to the point that none of the image is "in focus" at the CoC threshold.

....
The best answers that I received are: a) No camera has the direct mode for it by the numbers, b) With good eyesight and critical eye evaluation, one can use the the "preview" function / image, c.) one can carry a cheat sheet in your back pocket, d.) download "Camera Calculators" app to one's smart phone......I like answer c) the best and have downloaded it. It is quite simple and one can even specify you desired Circle of Confusion, or use a standard d/1500. But what c) does could be easily implemented with auto or semi automation as a mode in the modern "smart" camera.

Actually, it can't be easily implemented because most lenses don't electronically report an accurate physical subject distance to the camera and the DoF is extremely sensitive to the exact distance. (The camera may be "smart" but they don't get enough data from their "dumb" lenses.)

[clackers]

Real lenses have field curvature, too - apps and tables and algorithms never try to acknowledge that.

You can chimp in the field to your external monitor or tethered laptop and adjust focus and aperture, but if you're actually serious about the f64 look you combine several photos in postprocessing to get absolutely everything in the frame sharp. That's a standard operating procedure in landscapes, and nearly compulsory in astro.

[desertscape]

Real lenses have field curvature, too -

They do, however this is one of the seven major aberrations that designers correct. As such, field curvature is quite small and seen when the lens is wide open to a small degree. But this focal plane image curvature is masked by increased depth of focus when the lens is stopped down to any degree.

[clackers]

They do, however this is one of the seven major aberrations that designers correct. As such, field curvature is quite small and seen when the lens is wide open to a small degree. But this focal plane image curvature is masked by increased depth of focus when the lens is stopped down to any degree.

It's not, desertscape, field curvature is an important and individual effect in lens to lens … see here, for example:

Lens Rentals | Blog

No lens actually has a focal plane. It has a focal curve that can bulge at different points.

If you've got the DA15 or some of the Zeiss ultrawides stacking different shots is your best option.

[Tab Zee]

Oh dear. Now we are getting into the quality of lens design for a flat, curved or bumpy focal plane. I just want to know, quickly, what aperture to use if I'm shooting a 0.25 inch flower, a 5 inch flower or an elephant's head in the early twilight. I'm not a professional photographer. I'm not senile yet either, but I don't carry those numbers around in my head. The calculator serves my purpose, or a weatherproof cheat sheet in my back pocket. Yes, I forgot that the camera may or may not know the focus distance of the lens........ but yet the calculation would be more simple on the camera display than in my back pocket.... in dim light with my reading glasses in my right pocket...or did I put them in my left pocket................!!!.

[photoptimist]

Oh dear. Now we are getting into the quality of lens design for a flat, curved or bumpy focal plane. I just want to know, quickly, what aperture to use if I'm shooting a 0.25 inch flower, a 5 inch flower or an elephant's head in the early twilight. I'm not a professional photographer. I'm not senile yet either, but I don't carry those numbers around in my head. The calculator serves my purpose, or a weatherproof cheat sheet in my back pocket. Yes, I forgot that the camera may or may not know the focus distance of the lens........ but yet the calculation would be more simple on the camera display than in my back pocket.... in dim light with my reading glasses in my right pocket...or did I put them in my left pocket................!!!.

Brilliant suggestion.

Back in ye olden days of film, I had a tiny laminated table of hyperfocal distances that fit into the film box top holder on the back of my camera.

It sure would be nice to be able to call up some useful tables or apps on the camera display such as DoF (using lens focal length), flash guide number, angle of view, sunrise/sunset (using GPS), etc.

[rogerstg]

I remember using cheat sheets and notes in the days of film. Film could be a precious commodity when away. Now with digital and a little bit of experience, I find that I can take a series of shots at different apertures and focus points in less time than it takes to reach into my pocket for a note.
For example: a landscape where I want both a foreground object and infinity in focus:- I'd start at ƒ8 and focus at about double the distance of the foreground object. Then I might use ƒ13 and ƒ16. Finally, I'd probably repeat the same at a couple other focus points. The dials on the KP make it very easy.

It's practical and effective:
[url=https://flic.kr/p/2hd7ZJc]

[desertscape]

Back in ye olden days of film, I had a tiny laminated table of hyperfocal distances that fit into the film box top holder on the back of my camera.

Back in those olden days I used the DOF scale on the lens, realizing these scales were a bit too optimistic, I used the scales a bit more conservatively. Knowing the accuracy of your DOF scale on each lens was important. I still use lenses today with DOF scales. It works for me. With my 2 lenses without scales, I added hyperfocal dots for various apertures.