Y'all may remember a couple weeks ago I was testing my newly aquired 5D
and Tokina 28-80/2.8 and comparing the Tokina with some manual focus
Zuiko and non-Zuiko OM mount lenses. I reported that my Zuiko 28/2.8
appeared to have terrible optical performance which no one (including
me) could understand.
There followed lots of speculation centered on the camera's focusing
screen being slightly mispositioned such that it would cause front
focusing and I thought that's what was wrong.
Before futzing around with focusing screen shims to reposition the
screen I decided that I should be able to accomplish the same thing
(perhaps) by deliberately misadjusting the diopter control. I had
previously had it set at +2 clicks from its neutral position. The first
thing I noticed was that in resetting it I couldn't quite decide if +2
clicks or +3 clicks was the best setting. Anyhow I took one exposure
each at 0, +1, +2, +3, +4 and +5. Well, the +2 and +3 were a close-run
thing but I finally decided that my original choice of +2 was the better
one. And the +2 setting handily beat the others until... uh, oh! The
+5 setting was almost but not quite as good as the +2.
Suddenly, I had met the enemy and he was me!!! Back to the tripod and
take 3 more shots each at +2 and +3. Between each shot spin the
focusing ring and look away from the camera to force a completely fresh
refocus each time. I'm embarrassed at the results. Combining the first
set of test results with the second gave me four shots at each of the +2
and +3 settings. 2 out of 4 of both sets are terrible. Horribly soft
because horribly out of focus. 2 out of 4 of both sets are also
reasonably sharp. It's still a close run thing between +2 and +3 but
I've decided +2 is still the winner... so far.
Obviously the problem is that my old eyes can't do a decent manual
focusing job; at least on this target with this camera and screen. My
repeatability score is miserable.
I was going to do a little more testing but I've been chased away by
what may be a gathering thunder shower. Well, anyhow, I'm glad to have
the autofocus Tokina on the 5D. The two of them focus way more better
than Chuck.
ps: While testing I looked at the clear blue sky and see that the
finder is gathering dust already. Common 5D complaint. Don't know
about the sensor. Haven't checked that yet.
Chuck Norcutt
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