Archived posting to the Leica Users Group, 2001/02/09
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At 7:39 PM -0500 2/9/01, Martin Howard wrote:
>The LUG server limites messages over 10,000 characters -- maybe it's trying
>to tell me something ;) -- so this is posted in two parts. This is part
>one.
>
>austin@darkroom.com jotted down the following:
>
>>> Also, the films of today are much better at resolving fine detail than the
>>> films of 30 years ago -- yet our perception of DOF has not changed much,
>>> which would run counter to your argument.
>>>
>> How does that counter my argument?
>>
>Because you're making the claim that DOF is an objective property. If the
>materials have changed, then DOF should have changed too. Yet I can shoot
>the same scene on new film, printed on new paper, shot with a new lens, at
>the same aperture, printed at the same size, and viewed from the same
>distance. I will not see any difference in DOF. Contrast will probably
>change, meaning the prints will undoubtedly look a little different, but in
>terms of DOF, they will be the same.
>
>As for the claim that APO/ASPH lenses and new films require recalculation of
>the DOF, it doesn't hold up. If something is below the limits of human
>actuity, then it is below the limits of human actuity. It doesn't matter
>whether it's just under or 100x under, we will still not be able to see it.
Unfortunately, DOF as determined by the COC's commonly used is
_above_ the limits of human acuity. The resolution limit of the human
eye is about a minute of arc, whereas the COC's used are about 3 or 4
times that (see the 'Leica Handbook' article or any other full
description of Depth of Field). As per 'the Focal Encyclopedia of
Photography, third edition', points (or disks) with double the
spacing of lines can be resolved, which is still half the size
commonly used. Detection as opposed to resolution is possible already
at a value of 1/2 second of arc, or about 2 orders of magnitude
smaller. In any case, my previous description of the smaller COC's
needed when higher corrected lenses are used holds.
<snip>
- --
* Henning J. Wulff
/|\ Wulff Photography & Design
/###\ mailto:henningw@archiphoto.com
|[ ]| http://www.archiphoto.com