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Old Jan 24, 2011, 11:05 AM   #1
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Default Sony A33 artifacts vs Canon, Nikon

Trying out a Sony SLT A33 and bundled lense, noticed an artifact at high contrast edges - a hard purple outline, similar to chromatic aberation but on one side only. Images taken as RAW and converted using Sony's bundled utility showed the same purple fringe as ones taken as JPG, though image quality was better in general in the converted RAW version.

Test images can be found here - one distant and one macro, with crops and insets showing 400% enlargements of typical artifacts:

Some chromatic aberration in an entry-level lens is to be expected, and there does appear to be a bit of that, eg the Leaf image top right shows typical blue/red separation. However, there's also a broad purple 'shadow' that appears without a matching red shadow, and that's what's got me puzzled. It almost looks like a compression artifact, though unlike JPG artifacts.

Expecting this symptom to disappear in more expensive cameras, I gathered test cards for three Sony models, and similar models from Canon and Nikon. A composite of the top right corners of each testcard is included in the picasaweb album mentioned above.

The same purple fringing is visible in both Sony and Canon test cards - diminishing but still visible in more expensive Sony A850 and Canon EOS-1D Mark IV models.

However, it is virtually non-existent in the Nikons - the entry level D3100 has barely a hint, and the D7000 and D3S showing just a slight green/red edging on the large squares.

Which doesn't make sense - why would a high-end Sony or Canon show artifacts not seen in an entry level Nikon?

1. Default compression settings in Sony and Canon are more aggressive than Nikon. Turn that down and the purple shadow will go away.

2. The particular lens that I got was right on the edge of tolerances - a diffferent/better lense would greatly reduce the shadow.

3. Nikons put more money into the optics and algorithms, less into features like HD video, AutoHDR, etc.

4. The purple shadow doesn't matter - viewing at 400% is an unreasonable test, printers correct for shadows and you never see it in prints.

Soo, can anyone help sort this out? The A33 has amazing new in-camera features, and the phase-detect focusing in movies is excellent, but still image quality is my primary requirement, so may have to give up AutoHDR and focus-within-movies to get it.

Thanks in advance,
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Old Jan 24, 2011, 11:36 AM   #2
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The artifacts you're seeing all have the lens(es) as the root cause, exaggerated by camera settings and post processing.
  • The lens is the thing.
  • 'Full Frame' is the new 'Medium Format'.
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Old Jan 25, 2011, 1:56 PM   #3
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Thanks TCav,

I'll dive into lens reviews, see if things look better buying body and lens separately. I took one shot as both RAW and JPG, and there was a good bit of difference... so will drill down on that as well.

Basically, if shots can be gotten from the Sony of a quality approaching the Nikon testcards by using a better lens and shooting RAW or/or minimizing postprocessing, I'd love to have the new tech features like AutoHDR. Sounds like I need to sort out what the default post-processing settings are for the bodies I'm considering, make sure I'm comparing apples to apples.

Best regards,

Last edited by alphadog; Jan 25, 2011 at 1:57 PM. Reason: clarification
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Old Jan 29, 2011, 12:37 PM   #4
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Turns out Nikons have in-camera chromatic aberration correction - functionality also available in their Capture NX2 software product, as well as other software packages. The trial version did an excellent job on my Sony test shots, knocked CA down to levels found in the Nikon test shots.

And, finding quite a lot of difference in lenses too, so that's also part of the overall solution. Would love to go full-frame, but still just a bit out of my price range.
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