Popular Photo - DOF

Discussion in 'General Technical Discussion' started by Chris101, Sep 13, 2005.

  1. Chris101

    Chris101

    Feb 2, 2005
    Arizona
    Ok, you hate Pop Photo right! Sure - I do. They never say anything bad about an advertiser, and they reprint the same articles over and over.

    Well, I've got a confession. I've not missed an issue since 1978. Well, it was called Modern Photography for a while, but when Keppler and crew moved over, they changed names. And they have been the primary source of my photographic knowledge (well, in addition to about 50 other magazines, and in the last 6 years, online fora (like this place, DPR before that, and Nikon tech before that)) since digital.

    But guess what - that old media publication just came up with something new! Well, new to me anyways. It's about calculating the hyperfocal distance, a topic I have seen frequently. And wow! They have reduced the hyperfocal distance - the distance to focus at to get everything from the distant horizon to the closest thing you want to focus on, in acceptable focus, for any given f-stop - to a single 'easy to punch in to your calculator' formula:

    hyperfocal distance = '(focal length) squared ' divided by 'f-stop times 0.3'

    Cool, huh?
     
  2. Iliah

    Iliah

    Jan 29, 2005
    nowhere
  3. MontyDog

    MontyDog

    Jan 30, 2005
    #1064 - You have an error in your SQL syntax;
     
  4. Iliah

    Iliah

    Jan 29, 2005
    nowhere
    Dear Paul,

    0.3 is conversion from meters to feet, focal length should be in meters. If the lens is long, the formula is wrong

    Edit: ouch. I'm dense this morning. They got CoC wrong, probably. One of the ways to calculate is

    H = (FL*FL)/(f*CoC) + FL
     
    Last edited by a moderator: Sep 13, 2005
  5. Chris101

    Chris101

    Feb 2, 2005
    Arizona
    OUCH OUCH OUCH!!!

    Mea culpa! I copied but did not test this formula, and I made an error in reproducing it. Use 0.03 instead of 0.3 in the denominator. Here's what I get, with units in millimeters:

    FL=100
    FL^2=10000
    (f*0.03) = 0.24
    10000/0.24=41667mm=41.7m=137 feet

    Now remember, this is for 35mm film (cause the mag is like that) so ... this is pretty close to Nikonians DOF calculator value of 164 feet (which is a COC of 0.025mm - is this reasonable? Seems kinda big.)

    Here's what I don't get. APS film and 35mm film both give 164 feet, but the Nikon D100 and D2x, (the three I checked) give a hyperfocal of 205 feet (or a COC of 0.020mm.) Why the difference between film and digital of the same size? It's not related to pixel size because there is no difference between the D100 and D2x cameras with different pixel sizes.

    By the way, I couldn't find Thom's calculator, but these two are in agreement on 164 ft.: Nikonians and DOF MAster

    Thanks Paul & Iliah, I'm more confused than ever, now! :biggrin: :wink: :confused:
     
  6. Iliah

    Iliah

    Jan 29, 2005
    nowhere
    hehe. that was really amazingly hard morning :)

    Now, in the spirit of my everlasting love to bring controversy to any given simple topic let me say this: DoF calculations should be based on resolution of actual photographic process, not on arbitrary numbers which are not relevant any more. DoF for APS and FF film are the same because they use same resolution figures from 1930's. Zeiss warns against using those numbers in calculations. There are strong arguments that hyperfocal distance is not the best way to focus your camera - see the link in my prec. post, and this page at Norman Koren's site: http://www.normankoren.com/Tutorials/MTF6.html , under the header line "The myth of hyperfocal distance"
     
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