Ken Norton wrote:
> Yesterday, I finally got around to a little project that I've been putting
> off for a while. I wanted to compare resolutions of various lenses at all
> F-stops. The primary reason for this little project was determining which of
> my primes was the best "walk about" wide-angle to throw on an OM body. To
> test this, I used the E-1 and a trusty USAF line-pair res chart taped to a
> door. The res chart was printed on a single 8.5x11 sheet of paper centered
> on the door, and the picture was of the entire width of the door with trim on
> each side. Even with the 24mm lens, my closest distance was about two meters
> or so.
I think Chuck has a point with his comments on the diffraction-limited
effective resolution and find his exchange with C.H. interesting.
What I find odd is the methodology for evaluating 'the best "walk about"
wide-angle' for a full frame body.
Guessing a 30" interior door with narrow trim, I come up with 34".
Bigger just makes the numbers a little worse. Absent info, I've assumed
the target is placed horizontally.
That gives a lens coverage of 25.5 x 34" for the E-1. Scaling up height
to FF, then widening aspect ratio, I come up with coverage of about 47 x
70" for the same set-up with a FF body.
Assuming the target actually is representative of the whole 8.5 x 11"
central portion of the image, you are judging a lens based on 18% of its
linear height, 16% of width, or 3% of its area.
Traditional testing checks at least center and somewhere out near the
edge. Looking at Mike Hatem's tests of WA lenses, including several MF
Zuikos, it's clear that the middle zone between these two may also vary
significantly from them. The classic example is the Zuiko 18/3.5, which
both Gary and Mike show to resolve least in the very center, improving
as you go out. This test would show it as a relatively poor performer,
whereas test and practical results have show it to be one of the finer
SWA lenses ever made.
It's also often reported that individual lenses may vary in sharpness
between corners.
If I had the results of this test, I'd still be uncertain how they
pertained to the question of comparative individual overall lens
resolution on FF. I can see your dilemma, given the lack of a FF DSLR
and the considerable additional time and cost of doing a film based
test. Still, it does look suspiciously like "wasted effort" to me.
Maybe you shoudda bribed Chuck and Pat to stay an additional 1/2 day
with dinner and a show or something and shot the tests with his 5D and
more targets. :-)
Moose
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