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[OM] measuring lens performance

Subject: [OM] measuring lens performance
From: james king <jking@xxxxxxxxxxxxxx>
Date: Thu, 30 Mar 2006 13:42:51 +0100
I decided that it was time to try to have a go at measuring the 
performance of the lenses I have (both olympus and bronica partly to 
compare lenses across the two systems and partly because I was 
interested in the results.
I use the norman koren MTF chart a large 1m square peice of board and 
assembled a test target. I bought a x20, x50 and x100 microscope used 
fuji velvia 100F with an om4ti using mirror and app prefire and a cable 
release on the bronica. I have a beattie grid screen with 45 degree 
split in the om4ti and used the olympus varimagnifier to check focusing 
and a maxwell grid screen with horizontal split in the bronica and used 
its pop up magnifier.

I did the bronie first and was a little disconcerted by the results. As 
far as I could see at F8 and F11 I was not getting much output past 50 
or 60 line pairs per milimeter on any of the 7 lenses tested.

Yesterday I got the olympus tests back
olympus 24mm,28mm,35mm f2
         35-70 f3.6
         21 f3.5

tamron 90mm f2.5
tamron 80-200 f2.8 ed
tamron 60-300

the best of the results where no beter than the bronica in terms of line 
pairs per milimeter. I was careful to make sure that the mtf graphs are 
the same size on the film for both systems. Therefore the bronica shoots 
coverred more wall area than the olympus. What I did consistently 
observe was that wide open none of the 35mm film lenses could complete 
with the bronica lenses wide open but the performance of the tamron and 
olympus lenses did not degrade that much from f11 onwards. Whereas the 
bronica lenses do and at f32 the bronica lenses are nowhere near as 
sharp as the tamron 90mm at f32 for example.
So drawing a graph of performance vs appature the bronic starts fairly 
good open drops a little at the next stop and then is best f5.6-11 and 
then tails fairly rapidly. The 35mm film lenses are poor wide open 
improve and tail off in many cases very slowly.

Looking on the web good lenses are considered to be in the 80 line pairs 
per mm range and ziess claim 100 pairs plus for some of their lenses. I 
can see no way I can get anywhere near that with my setup...
It is possible that I am asking too much of the lenses and that easily 
visible line pairs at 50 or 60 pairs per mm on the film is all the 
camera system/experimental setup can do?

Regards
James






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