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CA Test: Sigma 30/2.8 vs. SEL1855

Discussion in 'Sony Alpha E-Mount Lenses' started by Hawkman, Dec 13, 2014.

  1. Hawkman

    Hawkman TalkEmount Top Veteran

    938
    Sep 10, 2013
    Virginia, USA
    Steve
    So, I recently picked up the Sigma 30mm f/2.8 DN Art lens on the recent Amazon Gold Box daily deal. Thought it was an unbeatable deal and wanted the 30mm focal length at a nice fast-ish aperture.

    However, after a couple of shots around the house, especially some outdoor ones of the house in good light, I noticed something odd... what appeared to be some color bleeding, but I quickly realized was noticeable (to me) chromatic aberration. I've noticed CA in shots from my other lenses, including the SEL50F18, but thought what I was seeing from the Sigma was... excessive.

    So today I did a couple of quick test shots of the branches of one of our trees against the sky. I shot the Sigma at f/5.6 on a tripod, and then shot the same spot with the SEL1855 set to 30mm and f/5.6 also. Looking at max magnification in iPhoto (which, as I later learned, is way more than 100% magnification) the Sigma shot had noticeably more CA, especially at the outer portions of the frame.

    So here is a 100% crop of the top right corner of the test shot of the tree using the Sigma 30, on a tripod to ensure as close to the same conditions between shots as possible. This is a straight export of the RAW image, no in-camera processing.

    16012935362_57e90f766b_o. CA Test - Sigma 30 by SRHawk64, on Flickr

    And next, the SEL1855.... Oddly, the SEL1855 had a faster shutter speed... maybe that was because I had left OSS on. Again, a straight export of the RAW image, no in-camera processing. To my eyes it appears the SEL1855 has noticeably less CA.

    15394003383_dab5cab9c0_o. CA Test - SEL1855 by SRHawk64, on Flickr

    What do you guys think? Am I imagining it or does the Sigma have more CA in these shots? And is this normal for the Sigma? Am I paranoid/overly-critical? Or should I send this copy back?
     
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  2. addieleman

    addieleman Passionate amateur

    Nov 13, 2012
    Netherlands
    Ad Dieleman
    I must be missing something because I don't see CA in the first picture. In the second picture there is some CA visible, but not too excessive IMHO. Now I don't know iPhoto so I don't know if it applies correction for CA like Lightroom does. In all fairness, most lenses for mirrorless cameras are designed with software correction for aberrations in mind. I have used the Sigma 30/2.8 a lot in the past, it was my standard lens on the NEX-6 and I've never noticed CA when processing the raws in Lightroom. It must be noted though that Lightroom does an incredibly good job in combatting CA and even purple fringing is correctible most of the time with some care.
     
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  3. bmg123

    bmg123 TalkEmount Veteran

    310
    Jan 15, 2013
    England, UK
    The Sigma clearly has more CA, but nothing that can't be corrected. I love the SEL1855 though, basically my main lens ever since I bought my camera back in January last year.
     
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  4. Hawkman

    Hawkman TalkEmount Top Veteran

    938
    Sep 10, 2013
    Virginia, USA
    Steve
    What I am seeing is a blue fringing on the right side of branches and a little red on the left sides. In these 100% crops it is not as bad as I thought, but still noticeable to me... and stronger than that for the SEL1855 at the same settings. Or so I thought.

    I've gone ahead and posted below another 100% crop, this time of a part of the image that clued me in to the whole thing in the first place.

    15836650280_37b540c68b_o. CA on Sigma 30mm f/2.8 by SRHawk64, on Flickr

    Note the rainbow discoloration on the downspout on the left, and also on the top of the window frame (the wavy nature of the vinyl siding near the window is real however, and not a camera issue). Note also the blue fringe on the right side of the window shutter edges and reddish fringe on the left sides. Am I seeing things or "making a mountain out of a mole hill"? Is this a case of serious chromatic aberration, something else entirely, or is it normal for the Sigma 30mm f/2.8 DN Art on Sony E-mount?

    Note that this is a 100% crop of a straight conversion from the RAW file... no post processing or correction applied other than RAW to JPEG export from iPhoto.
     
  5. addieleman

    addieleman Passionate amateur

    Nov 13, 2012
    Netherlands
    Ad Dieleman
    I get it. Looking at the "rainbow discoloration" I'd say this is moiré, not CA. Same for the top of the window frame. Your lens is too good! :)
     
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  6. dannat

    dannat TalkEmount Regular

    86
    Jun 22, 2014
    VIC
    yes moire -the lens is sharp enough to show it, i know DxO has moire correction -what PP software are you using?

    are you shootingwith the a3000 listed in your sig? maybe it has a weak aa filter -moire is usually only a problem with the cameras with no aa filter , eg A7s or nikon 800e
     
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  7. Hawkman

    Hawkman TalkEmount Top Veteran

    938
    Sep 10, 2013
    Virginia, USA
    Steve
    Moiré huh, I'll be darned. I didn't think the downspout or window had enough pattern to cause that. And thanks Ad, that does put my overactive mind at ease.

    Yes, I'm shooting with the A3000 (only E-mount camera I have so far). And now that you mention it, I do recall that DxOmark (or was it Imaging Resource) in their review of the A3000 mentioned that it appeared to have a less aggressive AA filter that enabled its 20Mp sensor to achieve details almost on par with the NEX-7's 24Mp sensor.

    And I'm not really using any PP software at the moment. I import everything through iPhoto, and occasionally use either Capture One Express for Sony or Intensify.
     
  8. Hawkman

    Hawkman TalkEmount Top Veteran

    938
    Sep 10, 2013
    Virginia, USA
    Steve
    Thanks again Ad for the heads up on the possibility of moiré. I again looked today at the structures and there is definitely a corrugation pattern on the downspout and a series of close parallel lines on the window top. Good call!

    So, while I do think there is some noticeable chromatic aberration, it's manageable and worth the tradeoff for all the Sigma 30 offers otherwise. Should be a keeper! Thanks!


    Sent from TalkEmount app on iPad
     
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