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02-27-2010, 12:07 PM   #16
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How to calculate hyperfocal distance, see Example at Hyperfocal distance - Wikipedia, the free encyclopedia

02-27-2010, 12:11 PM   #17
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QuoteOriginally posted by rustynail925 Quote
How do you compute the hyperfocal distance?
If your lens has aperture-distance scales inscribed on it -- almost all older primes, some older zooms -- the lens does the computation for you. I explained that in post #3 above. I also shoot film in some old folders that aren't marked, so I carry the little KODAK MASTER PHOTOGUIDE (available in many dusty thrift shops) which includes a DOF computer for 47-52mm, 70-80mm, 100-105mm, and 137-152mm. If I use an unmarked zoom that's beyond those ranges, I'm just S.O.L. (surely out of luck).

As for your 115/8 picture: I look in the Photoguide, extrapolate a little, and calc that if you hyperfocus at 50 ft, your DOF will be 25 ft to infinity. So f/8 is too wide - and that's working backwards, anyway. The front edge of your picture looks to be about 10 feet away, maybe less. How to get DOF of 10 feet (3m) to infinity? Argh, that Online DOF Calculator looks to be WAY off! Depth of field - Wikipedia, the free encyclopedia has some nasty-looking equations that I'll ignore. The Photoguide calculator suggests f/22, hyperfocus 18 ft, DOF 9 ft to infinity. A couple 90-100mm lenses (and some old zooms set to 115mm) say it can't be done - best DOF at f/22 is 20-25 ft to infinity. A couple 55-58mm lenses say f/16, hyperfocus to 20 ft, DOF is 10 ft to infinity. A couple 135mm lenses say the same, but af f/22. Ansel Adams (THE CAMERA) agrees with the Photoguide, but at 80mm, not 115mm. These scattered answers aren't very helpful, eh?

But it definitely looks like, except on a view camera, or with a tilt-shift adapter [ see Tilted plane focus - Wikipedia, the free encyclopedia ], it's hard get 10 ft to infinity DOF at focal lengths over 100mm on an APS-C camera, and hard to calculate the hyperfocal point. And you don't want to stop a lens all the way down to its smallest aperture anyway -- you start getting nasty diffraction effects. So:

* Mount a manual, marked 50mm lens (Takumar, Zeiss, whatever) on your cam;
* Set the INFINITY mark to just inside the mark for the next-to-smallest f-stop;
* The other f-stop mark should be around 6-8 feet; that's pretty good;
* Now you are in focus -- set the aperture; point the camera; shoot;
* In PP, crop the image so it looks like it was shot at 115mm.

Other options: Get an Olympus 4/3 system or any P&S with a sensor smaller than APS-C. The shorter lenses on smaller frames have greater DOF for the same FOV. (More noise, though.) Or get a view camera with a digital back and shoot at f/64. Or get a tilt-shift adapter -- but you may need to use medium-format lenses. Or stitch together a vertical panorama, with each tile being perfectly in focus, from 6 inches to infinity (I've done this). The easisest ways are probably: wider lens, and crop; and stitch-up. I'll stop now.

Last edited by RioRico; 02-27-2010 at 12:22 PM.
02-27-2010, 01:44 PM   #18
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Also, realize that these calculations are rough approximations only, based on "typcial" print sizes viewed form "typical" distances. A hyperfocal/DOF calculator might tell you something should be in focus but that doens't mean it going to look maximally sharp when pixel peeping. I think you're better off forgetting all the math and just do it by eye. Set the f-stop high, shoot somewhere in the middle distance, shoot, and zoom in on the LCD to see for yourself if you've got what you want. If the distance isn't as sharp as you want, focus further away. If that makes the foreground too soft, stop down more. It's neither magic nor rocket science.
02-27-2010, 02:38 PM   #19
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QuoteOriginally posted by RioRico Quote
But I can't control a viewer's eyeballs, and where and how she places them.
Of cuorse not. But that none of that changes the fact that if all else is equal (focus distance, aperture, print size, etc.) you will get less DOF from a larger sensor.

02-27-2010, 05:01 PM   #20
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QuoteOriginally posted by krb Quote
But that none of that changes the fact that if all else is equal (focus distance, aperture, print size, etc.) you will get less DOF from a larger sensor.
Come again? You have it backwards. If all else is equal, the smaller sensor requires more enlargement to bring it up to the same print size. Thus the print process has enlarged the Circles of Confusion of the image from the smaller sensor; it will look fuzzier. The less-enlarged image from the larger sensor will look sharper, will appear to have greater DOF, when viewed from the same distance.

Try it: shoot the same subject at the same exposure (speed and f-stop), distance/position, lighting, etc, and THE EXACT SAME FOCAL LENGTH, with an APS-C camera and a quality point-and-shoot. My Sony DSC-V1's Zeiss optics zoom out to 28mm. So we set the Sony to 3:2 aspect, put a 28mm Takumar on a K20D or whatever, set both apertures to f/5.6, shoot something at 1/100 sec with each. Now print each at, say, 30x20cm. The Sony's sensor has about 1/9 the area of the Pentax's. Do you really expect the more-enlarged print to look sharper, with greater apparent DOF, when viewed at arm's length?
02-27-2010, 05:31 PM   #21
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QuoteOriginally posted by Marc Sabatella Quote
Also, realize that these calculations are rough approximations only, based on "typcial" print sizes viewed form "typical" distances. A hyperfocal/DOF calculator might tell you something should be in focus but that doens't mean it going to look maximally sharp when pixel peeping. I think you're better off forgetting all the math and just do it by eye. Set the f-stop high, shoot somewhere in the middle distance, shoot, and zoom in on the LCD to see for yourself if you've got what you want. If the distance isn't as sharp as you want, focus further away. If that makes the foreground too soft, stop down more. It's neither magic nor rocket science.
Exactly. Because in the real world, estimating distances and trying to find a reasonable approximation of that distance on the focus scale if you have a scale is hard.
With the example scene, there is only beach where I'd want to focus. But there is plenty of light, so the above method is the best.

Also, I don't know why Pentax would build a lens that only works on APS-C with a distance scale for a completely different format.
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