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

Subject: [OM] 35-80/2.8: Distortion at 35mm
From: "Olaf Greve" <olaf_greve@xxxxxxxxxxx>
Date: Tue, 29 May 2001 08:19:08 -0000
Hi,

Joel wrote:

I have a 35-70/3.5-4.5 and 35-105/3.5-4.5. I am planning to reshoot the test for comparison purposes with these lenses, the 2.8 lens, and 35/2.8 shift later today. Thanks for your comments!

Excellent! I hope you can do the test using more or less the same strategy as I did (i.e. roughly 5m distance to a brick wall, $f5.6, lens' focal length settings: 35mm, 40mm and the long end (70mm/105mm)), so we can have some more or less similar pictures.

Ah, I used the same wall again for my shots. I checked the wall and it's not drunk ;)

Then Gary added:

The lens test page at:
http://members.aol.com/olympusom/lenstests/default.htm
already reports distortion and vignetting (fall-off) for all the Zuikos, including zooms at three different focal lengths (at least). I'm not sure what another testing round would prove. If there was any distortion differences to be had, it might be among the floating element designs at a closer focusing distance.

The idea (at least as far as I'm concerned) is not to see if you've got your distortion numbers right, but it's rather a case of "one picture says more than a 1000 words". In other words: the first picture I took for testing the barrel distortion was purely done to see just how much a picture is influenced by this at 35mm. When I see a statement like "pronounced barrel distortion at 35mm" it makes me aware that something is not optimal at that focal length, but then I still don't know exactly how much this will influence the resulting pictures. By taking sample shots using the worst case scenario (i.e. many straight lines @35mm) one directly can see the problem and one can keep this in mind as a "graphical recollection" of what straight lines will look like in these circumstances.

For me, the idea was to see if I should avoid the 35-80/2.8 at its 35mm setting for critical pictures, and if the image quality would improve a lot by using the 35/2.8 Shift for such pictures, hence my motivation for comparing the distortion of these lenses. I also decided to throw in the 35-70/3.6 into these comparisons partially out of personal curiosity, and partially because in some long off-list discussions between Erwin Voogt, Hnz and me (trust me, you guys DON'T want to know about this ;) ), it was suggested that the 35-70/3.6 might perform significantly better at the 35mm setting than the 35-80/2.8 would.

Finally, I also thought it would be interesting to graphically see just how much of this distortion would be present around 40mm, as well as to see if there's any visible distortion at the long end of the zoom range...

Cheers!
Olafo

PS: Erwin: you're one of the "enablers" of these tests, so we do want to see the results you mentioned you obtained with the Tokina 35-70/2.8 someday too ;)
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