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Re: [OM] ( OM ) Lens tests - comment

Subject: Re: [OM] ( OM ) Lens tests - comment
From: Winsor Crosby <wincros@xxxxxxxxxxxxx>
Date: Thu, 7 Nov 2002 08:30:46 -0800
Hi folks,

As has been obvious, I've been looking at lens tests and lens capability with
more than usual interest during recent months. Spurred on by things done in
conjunction with this group.

During the last week or so I've been looking at lens tests done during the last
3 - 4 years, and two aspects seem apparent; at least for some of the lenses.

(a) Some of the lenses have quite excellent resolution and contrast - much
ahead of lens performance of 15 - 20 years ago.
(b) Some of the lenses actually have their best performance (by these
criteria), wide open or near maximum opening.

Brian

Lens tests are fun, but I think you have to be careful in jumping to sweeping conclusions. A lens test result is just the result of a method and operator that day. Nothing absolute is revealed about the lens. Years ago when I devoured these things I discovered a few tests of the same serial number lens the results of which were in conflict in spite being nominally the same test method. Tests are very subjective in spite of the "facts and figures" format.

Different tests methods are not directly comparable either. Certainly there has been no consistent method of testing for a long period of time. Tests done 20 years ago cannot be compared to tests done today because the methods may be different. Even if the methods are nominally the same the details of practice will vary over time and with the individual technician.

Anyone who has ever taken a lab course in science will tell you that experimental results will vary all over the place depending on who is doing the experiment even in optics. There are good technicians and not so good. Probably the best(most consistent) testing is done by one person over a short period of time by someone who works hard to reduce variability as Gary Reese did. I would bet that even Gary would admit that some of his early tests were not entirely consistent with the later ones. I am sure that his judgment of sharpness improved with practice. Certainly he noticed the problem introduced by the aperture mechanism using the OM 1 and tried to isolate that later and redid tests in order to isolate the problem.
--
Winsor Crosby
Long Beach, California


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