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[OM] The 5D and manual focus OM lenses

Subject: [OM] The 5D and manual focus OM lenses
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxx>
Date: Sat, 17 Jun 2006 18:11:16 -0400
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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