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06-25-2013, 09:47 AM   #1
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Chromatic aberration on a 77mm Limited?

Hi all,

I have purchased a 77mm Limited Lens on ebay the other day. It arrived today so I started testing it with my K5-II and noticed a very strong chromatic aberration. At least much stronger than on other lenses I have (50mm-pentax, 17-50mm-tamron). I read in several places that chromatic aberration should be no problem with this lens (see here)


Is this normal or is there something wrong with this lens????


Any feedback appreciated.




Here are some pics with the 77mm pentax limited:

http://oi39.tinypic.com/11liuds.jpg

http://oi43.tinypic.com/10i8p78.jpg




http://oi40.tinypic.com/30j661e.jpg

Here is the same shot with my 50mm/1.7 pentax

http://oi39.tinypic.com/xc1xsm.jpg

Here is the same shot with my 1-750mm/2.8 tamron

http://oi40.tinypic.com/zmcb2x.jpg

06-25-2013, 10:16 AM   #2
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Well known for PF. Read through the lens reviews here SMC Pentax-FA 77mm F1.8 Limited Reviews - FA Prime Lenses - Pentax Lens Reviews & Lens Database
06-25-2013, 10:29 AM   #3
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Yes, perfectly normal purple fringing. See here:

Purple Fringing - Wikipedia

The FA 77 was designed for film, which is not sensitive to this phenomenon. It simply wasn't considered when the lens was designed. My 50-year-old Helios 40 fringes like mad. When you read that a new lens has coatings "optimized for digital" (your Tamron is one of these), this is one of the big things they're talking about.

Not to worry, though. Purple fringing is easily fixed by post-processing software such as Lightroom.
06-25-2013, 10:32 AM   #4
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I don't see any CA, but there is Purple Fringing (not an optical lens aberration per se). Depending on sensor and subject, you may expect some of this with the 77 Limited and many, many other lenses. Fortunately, it is easily dealt with in post-processing.


Steve

06-25-2013, 10:41 AM   #5
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Purple Fringing

Hi Everybody,

thanks for your replies. I now see that purple fringing is normal for this lence. So there is nothing to worry about.

@JohnX: I read the review, and I saw the pictures, but they didnt appear to me having that strong of a PF. Especialy that white dog on black background. So I was wondering about it.

Cheers
MP
06-25-2013, 10:50 AM   #6
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QuoteOriginally posted by magic.pill Quote
but they didnt appear to me having that strong of a PF. Especialy that white dog on black background. So I was wondering about it.
They probably removed it in post, since it's so easy to do.

Edit: actually, that's a black and white picture. You can't get purple fringing in black and white, silly!
06-25-2013, 11:14 AM   #7
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Among older lenses (and even some newer ones), it seems to be the very sharpest ones that PF the most. I expect as sensors and post-processing continues to improve, this will be less and less of an issue...
06-25-2013, 11:23 AM   #8
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Is it really so easy to remove, though? Some software has a tool for it, but in my experience its not very effective. You can desaturate all purples, but thats not really an option if you have anything else in the photo that is also purple.

06-25-2013, 11:43 AM   #9
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A smart algorithm will not go after all purple in an image, but only after the purple that's isolated along high-contrast edges, so genuinely purple areas will not be affected.
06-25-2013, 12:30 PM   #10
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Most algorithms not too smart yet, but Lightroom 4 makes it fairly easy to isolate areas you want by both color value and area of picture. (It will also give you a preview of areas it is affecting...)
06-25-2013, 01:04 PM   #11
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QuoteOriginally posted by vonBaloney Quote
Among older lenses (and even some newer ones), it seems to be the very sharpest ones that PF the most. I expect as sensors and post-processing continues to improve, this will be less and less of an issue...
I have being wondering about this. I have a sharp copy of a Samyang (Bower) 85 f1.4 that is the sharpest lens wide open I have and it exhibits quite a lot of PF at times - even though other peoples reviews don't generally complain about this aspect. Its not the end of the world though - I would rather have the sharpness than no PF (and no sharpness)!
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