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01-05-2013, 09:28 PM   #31
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QuoteOriginally posted by vonBaloney Quote
If "digital only purple fringing" wants to be in a special category, it needs a new name...
Historically, the new name is "Purple Fringing". The term was coined over a decade ago in regards to false color on digital images that could not be explained as typical CA (axial or lateral). It is literally a term of the digital age that describes something that happens with digital images, both still and video.


Steve


Last edited by stevebrot; 01-05-2013 at 09:37 PM.
01-05-2013, 09:45 PM   #32
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QuoteOriginally posted by Digitalis Quote
The Canon EF85mm f/1.8 - which is a good comparison for the FA77mm f/1.8 - also shares a tendency to PF on APS-C and Full format sensors. So if the FA77 does it on a pentax camera you can bet it will do it on any other makers camera.
This is a good point. Klaus at photozone.de seems to feel that it is a property of large aperture lenses in general and might be related to the contrast latitude of the sensor. His review of the FA 77/1.8 Limited has a good discussion of PF vs. CA (both lateral and axial).

http://www.photozone.de/pentax/128-pentax-smc-fa-77mm-f18-limited-review--test-report?start=1

Klaus does refer to PF as a type of CA, and perhaps it should be termed that way, if only it could be reproduced on the optical bench.


Steve

Last edited by stevebrot; 01-05-2013 at 09:51 PM.
01-05-2013, 10:05 PM   #33
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QuoteOriginally posted by vonBaloney Quote
That's right -- I don't believe there is plain M 300/4, it only came in a green star(*) version. It is known as a fantastic lens, and is completely different than earlier K 300/4, which I don't think is that well-regarded, fringing or not.
The lens database here tells a story for each lens. I wouldn't say the K300 4 is not well regarded: it actually gets 9s & 10s in the reviews. It is splendidly built, very sharp, wide open even, & has nice MF ergonomics. There are lots of complaints concerning a lack of tripod mount, but the Ca issue is not consistently experienced by reviewers. The overall mean score is unduly affected by two, very low scores of 1 & 3. In both of those reviews, words like "terrible ca" and "bad fringing" abound, which leads one to believe sample variation must exist to a large degree.

JT

Last edited by Jewelltrail; 01-05-2013 at 11:05 PM.
01-05-2013, 10:13 PM   #34
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QuoteOriginally posted by stevebrot Quote
Historically, the new name is "Purple Fringing". The term was coined over a decade ago in regards to false color on digital images that could not be explained as typical CA (axial or lateral). It is literally a term of the digital age that describes something that happens with digital images, both still and video.
Again, if someone is looking at something that is LITERALLY a purple fringe, and you're telling them "That is not purple fringing" it just doesn't make much sense, and there will be no hope of ending confusion as long as you insist purple fringes are not purple fringes.

01-12-2013, 04:55 PM   #35
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Purple fringing (PF) can be caused by lens chromatic aberrations (CA) as well as by other things. And lens CA does not always manifest as PF. But because lens CA is one cause of PF, there definitely are differences between lenses with regard to PF.

I have or have had most of the common/ cheap M lenses and a couple less common ones: 28/2.8 (I), 50/1.7, 50/2, 100/2.8, 120/2.8, 135/3.5, and 200/4. I've never done a controlled PF or CA test except between the 100, 120, and 135. Among these three, the 100 and 135 are both pretty bad, the 120 noticeably better. I don't tend to shoot 50mm in the sort of situations where PF would manifest, so it's hard to say with those. The 28 seems about average with respect to PF.
01-12-2013, 05:17 PM   #36
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QuoteOriginally posted by vonBaloney Quote
Again, if someone is looking at something that is LITERALLY a purple fringe, and you're telling them "That is not purple fringing" it just doesn't make much sense, and there will be no hope of ending confusion as long as you insist purple fringes are not purple fringes.
I too, would prefer a better term that does not require a background in optical aberrations to understand, though I can understand how it came about. Not that many years ago people started buying digital cameras and soon were complaining on the various online forums about purple fringes on high-contrast borders. It is jargon, nothing more and nothing less.

As Marc says, CA may cause a purple fringe, but not all fringing is CA. Lacking a better term, I will continue to follow the lead of photozone.de and limit my use of the term Purple fringing (PF) to that which cannot be accounted for by CA. Alternatively,I suppose I could refer to it as

"purple boundary artifact that is not CA and which is limited to digital cameras and which may be the result of optical or physical properties of a particular lens in conjunction with digital sensors whose severity may vary according to the sensor technology in question"

because that long phrase pretty much sums up what we know about the phenomenon.


Steve

(...and yes, there is some opinion that CMOS sensors are less prone to PF than CCD sensors...)

(...strange that the makers of both cameras and lenses are pretty much mum about whether their products are better or worse than average in regards to PF...)
01-12-2013, 09:15 PM   #37
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One of the contributing factors to the appearance of Purple fringing (PF) is lens contrast - lenses with higher contrast eg,FA77,FA31 will produce it at wider apertures - stopping the lens down does not remove PF, it simply makes it less apparent. The SMCP-K 50mm f/1.2 has lower contrast at f/1.2 and therefore the PF doesn't appear to be anywhere near as bad as the FA77 - in comparison: the Canon EF 50mm f/1.2L which suffers from visible PF all the way to f/8, the pentax 50mm f/1.2 has a considerable advantage over the canon L lens in regards to this particular fault.


Both these images are from a Pentax K10D - which uses a CCD sensor, though I doubt that sensor architecture has much to do with the effect. We have all seen varying amounts of PF from different lenses and the only lenses that do not have it are apochromatic or make extensive use of exotic glass types with low dispersion.
01-13-2013, 03:48 PM   #38
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I'm still curious about the possible cause of PF myself, but one thing I noticed: off all the Pentax DSLRs I've ever owned (K10, K20, K7, Kx and K5), the K5 seems to be really prone to PF, to the point where I seriously considered returning it...
And all where used with pretty much the same lenses collection, so...

But the effect is way too much "optical-like" for it to be a sensor-only blooming or whatever, IMO... Anyway, I thought that blooming was actually a thing of the past (and concerning CCD only!)..
Or maybe PF is some kind of heat propagation, just like we can sometime see on the borders of high-iso pics...

01-13-2013, 04:57 PM   #39
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QuoteOriginally posted by dlacouture Quote
just like we can sometime see on the borders of high-iso pics...
That is amplifier glow, which is different from PF

One argument is that PF is a digital only phenomenon. I can tell you that it isn't, you see PF in film, like Blade Runner* the Shining, Kill Bill - Cine lenses are considerably more expensive and are built to exacting standards and are optically superior to many 35mm photographic lenses. You don't see many optical aberrations in films these days - because a majority of it is filtered out in post production - though there are some scenes in the Pirates of the caribbean where you can see some horrendous transverse CA which is common when lenses that are optimised for distant subjects are used for close up-macro work, most of those movies were shot with Zeiss Ultraprime lenses.


*when Deckard interviews Rachel. In the shining you see it when the family is given a tour of the Hotel. In Kill Bill you see it when Kiddo is with Hattori Hanzo looking at Katanas and PF also appears in the fight against O'ren Ishii.

Last edited by Digitalis; 01-16-2013 at 02:22 AM.
01-15-2013, 11:59 PM   #40
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QuoteOriginally posted by Digitalis Quote
*when Deckard interviews Rachel.
Interesting...I will have to take a look at that scene.

I have been spending a fair amount of time scanning 35mm slides from the archives and have seen several that almost assuredly would have generated PF with the same lenses on my K10D, but which have none, nada, nothing.

I am not saying you are wrong. I have tremendous respect for your technical expertise.


Steve

(Specifically thinking about this image (LINK). Even at 4000 dpi...no PF in those specular highlights.)
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