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Re:[OM] OM to EOS Mount Adapter

Subject: Re:[OM] OM to EOS Mount Adapter
From: "Tomoko Yamamoto" <tomokoy@xxxxxxxxx>
Date: Wed, 16 Jun 1999 11:59:53 -0400
Here is some results of the OM lens performance on the EOS 1n with the mount
adapter in my hands.

Yesterday morning I put two rolls of film through the EOS 1N with the OM-to-EOS
adapter.  I used the following Olympus lenses:
20mm/3.8 (really Cosina in OM mount)
35-70mm/3.5-4.5
85mm/2
100mm/2.8 + B300 (1.7x teleconverter made for the IS-3)

With the 85mm/2 shots I used a relatively-heavy Bogen tripod and the
edge-to-edge sharpness was not a problem at all.  I used Velvia and the
exposure was good also. The subject was the still neighborhood in mid-day
lighting with the 85mm/2 shots.

Now if I remember correctly, I changed the dioptric correction setting on the
EOS before I did the Velvia roll with the 85mm/2.  This might account for some
near-side softness in the earlier morning shots.

With the other lenses I used the EOS 1n and the 4T hand-held at a sandy beach of
a reservoir outside of Baltimore.  The near-side objects are small pebbles on
the beach and at the far-end are deciduous trees in the woods on the opposite
shore.
By the time I got to the spot about 9 in the morning, the clouds had started
covering the sky and sunlight was intermittent.

The 20mm Cosina gave fairly good results.  Near-side sharpness was good (larger
objects nearby) at the right-hand corner, but in another frame in which
near-side objects are in the left-hand corner, the sharpness was not as good
judging from projection (22x33 inches). While I could not tell the far-end
sharpness at infinity well, but I would say it was better in the slide with the
right-hand corner sharpness than in the slide with the softer left-hand corner.
Part of the problem with these two shots is exposure because of back lighting in
the latter.

I have used both the OM-4T and the EOS-1n with some of the lenses.  Here is my
comparison using an 8x loupe.

70mm end of the 35-70mm/3.5-4.5
4T: shadow at near-side underexposed, soft corner
      sharp at far end
EOS:O.K. exposure, moderately sharp nearby
         a bit soft at far end, but acceptable
35mm end of the 35-70mm/3.5-4.5
4T: sharp throughout
EOS: soft at left-hand corner nearby
100mm/2.8 + B300
4T: bottom-end resolution fair
      log in the middle sharp
      far-end wood underexposed poorly resolved
EOS: slightly different composition  soft at left-hand corner
         log closer to the bottom sharp
         far-end trees in the wood sharp

Since it is possible to obtain edge-to-edge sharpness with the 85mm/2 on a
tripod, I can rule out any problem with the mount adapter.

The inconsistent results might be due to a few different factors:
camera shake with the EOS
wrong dioptric correction leading to wrong focus point?
improper exposure including too slow shutter speeds to stop the leaves

I used  pan-focusing particularly with the wide angle lenses, but I may not have
done this consistently.  I also recall that I forgot to open the aperture wide
when focusing, which made it moderately difficult to ascertain the accuracy of
focusing. Since the 70mm shot with the EOS gave  moderate sharpness at the near
end, the camera shake may not be that serious with the 35-70mm lens.

I did test the EOS with the mount adapter using the 85mm/2 and a manual flash
outdoors. I am afraid I did not do an expert job (there were some over-exposed
shots
due to flash too close, but I did get good shots using AEB), but I can say that
flash synch on the EOS 1n has nothing to do with the mount adapter.  If you
experience any flash problems with your EOS 1n, that would be an electronic
problem.  The mount adapter does not have any optics nor electronics.  It is
simply a mechanical spacer and the mount size reducer for the OM lenses.

Tomoko Yamamoto
mailto:tomokoy@xxxxxxxxx
http://www.charm.net/~tomokoy/







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