I've been thinking about DOF and this old post. I just didn't see where
such big differences could come from. I just looked at the DOF tables
for the 100/2.8 and the 35-105. They are both on the eSIF, but the 100/2
is not. The DOF tables for the zoom at 105mm and the 100/2.8 are
virtually identical. The markings on my 100/2.8 agree with Brian's and
the tables.
I can only conclude that the markings on the zoom assume it is a
consumer lens and use a bigger circle of confusion than the tables,
which both use 1/30mm, assuming a 4x6 mass produced print standard.
Notice that the barrel markings on the 100/2, a more 'professional' lens
than the 2.8, have an even tighter DOF.
A couple of examples:
100/2.8, f22, focus at 30m, DOF = 9.58 m-inf.
Zoom@105 f22, focus at 50m, DOF = 9.50 m-inf.
100/2.8, f22, focus at 2m, DOF = 1.78-2.28 m.
Zoom@105 f22, focus at 2m, DOF = 1.78-2.29 m.
I'm willing to bet a 50/1.8 that the table for the 100/2 is the same as
the 100/2.8 within 1/10 of a meter, if using the same circle of confusion..
I don't know who Dr Kornelius J. Fleischer is, or what his credentials
are, but I wonder how accurate his post is. He is talking about a super
resolution long focus lens and is hung up on the exceptional resolution,
so what circle of confusion is he using, either in his viewing judgment,
or actual measurement/calculation? I expect he is correct that DOF for
the same FL can vary with lens design, but that the variation is tiny
with conventional designs.
In any case, Brian, if you are using the DOF markings on the zoom, you
are going to have trouble with sharpness.
Moose
Brian Swale wrote:
DOF.
I don't know how much notice one should take of the DOF scales engraved
on lens barrels, but this is what some of my lenses have. Because this
thread came out of a remark I made about the Zuiko 100/2, these are all
lenses set at 100mm focal length.
F stop 22, one end of the line on infinity.
The other line fell on the following distance (metres)
100/2 10
100/2.8 7.5
35~105 4.75 (this was difficult to be sure as there is no f/22 line on this
lens, but if there were, judging from the spacing of the other lines, that's
where it would be.
F stop 16, one line on infinity
100/2 14.6 (difficult to be sure - about 48 ft - doesn't have line for f/16)
100/2.8 8.5 (difficult to be sure - no f/16 line)
35~105 8
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