 James Gregus |
What is Hyperfocal?
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Tony Sweet |
James, quite simply, and avoiding the physics explanation, hyperfocal is a function of wide angle lenses. First off, you need a "near-far" relationship... something close and something far away. Set your lens at f/22 and focus 1/3 third into the film plane, NOT the scene. In other words, focus at the 1/3 point in the frame. Make sense?
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Jon Close |
Hyperfocal is the nearest distance at which infinity falls within the depth of focus. When the lens is focused to the hyperfocal distance, depth of field will extend from about 1/2 that distance to infinity. It is a function of lens focal length, the aperture set, and the minimum "circle of confusion." The circle of confusion will vary by the size of the film format used, generall accepted as .025mm for 35mm film. The formula for determining the hyperfocal distance is f^2/(F x d), where f^2 is the focal length squared, F is the aperture number, and d is the circle of confusion. Examples: For 50mm and f/16 the hyperfocal distance is 6.25 m (~20.5 ft).
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James Gregus |
Thanks to Tony Sweet & Jon Close for your information on hyperfocal distance. I'll try what you said and see how it works.
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John A. Lind |
James, While you've been given some heuristics, and Jon has presented some of the math surrounding hyperfocal distance, it's still not quite that simple. Reason? The circle of confusion diameter is derived from several factors: print size, print viewing distance (or projection size and projection viewing distance for slides) and generally accepted acuity of the human eye. IOW, depth of field is based on human perception. The *only* distance completely in focus in a photograph is the focus distance you set the lens for (critical focus). Something must be sufficiently out of focus before it will appear to be to the unaided human eye. I am pleased to see Jon is using the tighter 25/1000ths mm for CoC diameter. It will likely lead to less trouble. Some depth of field models use looser values (as large as 0.033mm). The caution here is to understand that the larger you make the print and closer you view it, the more the apparent depth of field shrinks. What appears to be OK in a 4x6 print may be disappointing in an 8x10 or 11x14 size print . . . and I have seen 8x10's that were obviously done using a "hyperfocal distance" based on smaller print size. I won't go into the equations here (too much and too many), but will walk through the concept: Remember to keep units of measure the *same*. I convert everything to millimeters before grinding out the numbers. Also remember when doing the trig you are working with a diameter, not a radius.
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BetterPhotoJim.com - Jim Miotke  Contact Jim Miotke Jim Miotke's Gallery |
Hi James, I also wanted to point out a few helpful depth of field charts that John Lind uploaded a while back:
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James Gregus |
Hi Jim, You and everybody else has help me out alot. Thank you for all your help. James Gregus Designs by Gregus
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Artur |
Hi James, if you look at your lens on top you will see two scales, one that is turning with a lens when you adjusting focus and second that is not moving. Second have a mark in the middle to show your focus distance on the first scale and marks to left and right with aperture numbers. Set your aperture to the highest number like f22 and than rotate the lens until the infinity mark lines up with mark on the lens corresponding to f22 on the right side of the middle mark. Now read the distance on the rotating scale that is lined up with mark on left side corresponding to f22, that is your minimum distance that is in focus. Your lens is set to hiperfocal distance and every think from that minimum distance to infinity will be in focus. Artur
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John A. Lind |
What Artur states is correct. One caution about doing this though. Lens scales are not necessarily marked well. Run the math out to see what the lens designer decided the circle of confusion diamter is . . . and check its accuracy with known distances. Once you've "calibrated" the focus scale on the lens, this method works (as adjusted for the testing done to calibrate the focusing scale). I've done this with a number of lenses from a number of different manufacturers. The CoC diameter assumption varies all over the map . . . from 0.033mm for one brand of lens (cannot remember which) to 0.025mm for a Rollei Zeiss lens. For those that ran on the high side with CoC, I simply set the hyperfocal distance for one f-stop wider than will be used (this puts a "guardband" around the near and far depth of field limits). -- John
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