Is this the expected corner performance of Olympus M.Zuiko ED 75-300mm f4.8-6.7 II ?

Started 4 months ago | Questions thread
milek
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In reply to milek, 4 months ago

I ran some more experiments tonight.

Summary:

I'm keeping the lens. My previous experiments were made from too close a distance.

More details:

When I enlarged the resolution chart and increased the distance to 3m/10ft, the performance in the corners increased a lot. Thank you, jhinkey and CrisPhoto for your useful suggestions to that effect and in particular thank you, Christof, for sharing the shots from your past experiments.

The funny thing is that I was testing two other lenses at the same time at the same focal lengths: Oly 14-150 and the old 4/3 Oly 70-300 (with a Panasonic adapter), and they were a lot better behaved at these close distances. So it must be something about the optical formula of Oly 75-300 where it's just particularly prone to poor corner behavior at close distances.

New result at 75mm wide-open.

Actually, while three corners improved markedly with increased distance, one (bottom-right) not so much. It is softer for focal lengths under 150mm and apertures under f/11. So my copy of the lens is not flawless, but, as CrisPhoto pointed out, that is not surprising at this price point. I can live with that, particularly since the long end does not appear to be affected, and I obviously agree that the long end is what we buy these lenses for (the reason I've been showing results from the short end is that the problem was more visible there; as we all know, Oly 75-300 is not as sharp at the very long end).

Regarding the discussion of mk1 vs mk2, it's indeed so hard for us individual users to tell what is a copy to copy variation and what is not... I was under the impression that the MTF charts were the same for both, so I assumed that slrgear tests would remain relevant. Also, Ephotozine saw the same (good) corner performance with mk2, although unlike slrgear they don't include resolution chart shots among sample pictures (bummer!).

With respect to pixelation artifacts in my shots, it's actually an interesting story. I have a 600dpi laser b&w printer which normally produces razor-sharp results, so I was a little surprised by that myself. Today I inspected it more closely and it turned out that the resolution chart available online does *not* use black, but dark grey. The printer was using halftones to represent the shade, hence the pixelation. Today I converted the PDF to black and white and reprinted it in a larger format, and you know what? I was actually missing the pixelation when checking the results! The pixelation was really helpful in telling sharp from almost sharp.

Also, thanks for the suggestion about the flash. I normally never use it with a tripod so it hasn't even occurred to me, but it turned out to be quite helpful here, as not only were the shots better lit, but the printer toner also reflects light a bit, resulting in a subtle pattern that helps when comparing resolutions between shots.

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