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Re: [OM] 35-80/2.8: Distortion at 35mm

Subject: Re: [OM] 35-80/2.8: Distortion at 35mm
From: Winsor Crosby <wincros@xxxxxxxxxxxxx>
Date: Fri, 25 May 2001 11:31:26 -0700
I performed my own little test of distortion with the 35-80/2.8 at 35mm. I tried but didn't successfully get the film plane precisely parallel to the wall, so I don't think these tests are definitive by any means, but I think it is still possible to get an idea of the problem.

There are three frames: 1) 35-80/2.8 at 35mm, 2) 35/2.8 shift (unshifted) for comparison, and 3) 35-80/2.8 at 40mm (to see at what stage the problem goes away)

I made shots at 40mm, 45mm, and 50mm to see at what point there is no longer any distortion. I didn't include the 45mm and 50mm shots because I felt the distortion was gone at 40mm. There almost looks like a waveform distortion in the 40mm shot, though focus is not as good and the lines of this wall are not ideally straight for tests of this nature. (Live and learn.) I probably should have focused directly on the wall, but I didn't (the main subject is the red pump). The difference in DOF between 35mm and 40mm at f4 may be a factor of some sort.

At least from these shots I will be operating henceforth under the assumption that distortion is basically gone by 40mm. The 35/2.8 shift shot gives one a reference on the quirks of the wall itself, and in relation to that the 40mm shot looks quite good to me.

Anyway, see for yourselves here:

http://soli.inav.net/~jdub/35distortion.html

Joel W.


There is also, apparently, a little darkening in the corners for both the 35mm shots. Were these wide open?
--
Winsor Crosby
Long Beach, California, USA
mailto:wincros@xxxxxxxxxxx



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