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01-05-2013, 11:48 AM   #16
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QuoteOriginally posted by Jean Poitiers Quote
Please do tell ...
Ok...
  • FA 77/1.8 Limited (very, very slight)
  • DA 18-55/3.5-5.6 (v1)
  • KMZ MC Zenitar 16/2.8 Fisheye
Overall, plain old CA is a more consistent problem across the board with the lenses I own and is a concern more from the perspective of degraded sharpness than false color. (I do a fair amount of B&W film work.) You may note that the FA 35/2 is absent from the list. Maybe I have a very special copy, but I have never seen PF from that lens, despite the example photo at photozone.de!


Last edited by stevebrot; 01-05-2013 at 12:14 PM.
01-05-2013, 12:12 PM   #17
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QuoteOriginally posted by Stone G. Quote
...most films had and have a rather different spectral sensitivity than digital sensors, whether with or without blocking filters. See for example: Wikipedia:

Purple fringing - Wikipedia, the free encyclopedia
I am familiar with this article and always found the first example photograph to be amusing. I have seen severe PF and that is not it When I think PF, I generally think of a wedding shot where the bride's arm is purple from wrist to elbow! Or perhaps the more classic bare branches against sky where the branches are "webbed" with violet glow. Beyond that, the author of the article is pretty clear that he is describing CA (both lateral and axial) and offers the hypothesis that the digital sensor amplifies the problem.

An interesting matter for discussion is the fact that some lenses that are supposed to be notorious for PF have very low measured CA (the FA 35/2 and FA 77/1.8 being prime examples). Klaus at Photozone is always careful to make a distinction in his lens reviews. It is also good to note that CA usually increases from large to smaller aperture while PF decreases.

For what it is worth, most films (color and b&w) have significant blue-end sensitivity extending into the UV. This traditionally has been problematic in terms of blue shift due to reciprocity failure on long exposures and unwanted haze for landscape work (hence the common use of a UV filter for color work). If the lenses were optimized for film sensitivity, one would expect that the blue end of the spectrum would be more accurately focused, not the other way around.


Steve

Last edited by stevebrot; 01-05-2013 at 12:33 PM.
01-05-2013, 12:32 PM   #18
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Here's an interesting article on CA and PF.
Chromatic aberrations
01-05-2013, 12:37 PM   #19
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Seems to me that the lens AND to a lesser degree, the sensor are implicated in purple fringing. I have seen convincing examples of fringing caused by the sensor, and have personal experience of lenses causing the issue.

01-05-2013, 12:54 PM   #20
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QuoteOriginally posted by ihasa Quote
Seems to me that the lens AND to a lesser degree, the sensor are implicated in purple fringing. I have seen convincing examples of fringing caused by the sensor, and have personal experience of lenses causing the issue.
And I feel just the opposite, primarily because of my background in film photography and my history with digital. I think that the issue can be summed nicely without determining an absolute cause:
  • Purple false color can be caused by CA (both lateral and axial)
  • CA is a fault of optical design and a characteristic of the lens
  • Purple false color can also be present when measured CA is low
  • Purple false color is more prevalent with some lenses than with others
  • Non-CA purple false color is absent from film images and is most likely caused by an interaction of lens and sensor on digital images. A number of causes have been postulated.
I would curious if anyone has ever seen a comparison across sensors for adapted lenses. For example, does the FA 77/1.8 have PF on Canon APS or Canon FF? I have a couple of local friends that shoot Canon. Perhaps it is time to do a little comparo?


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01-05-2013, 01:01 PM   #21
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You say it yourself, purple false color is more prevalent with some lenses than others.
01-05-2013, 01:03 PM   #22
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QuoteOriginally posted by Swift1 Quote
Here's an interesting article on CA and PF.
Chromatic aberrations
An excellent article with great illustrations.


Steve
01-05-2013, 01:18 PM   #23
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QuoteOriginally posted by stevebrot Quote
Wrong...PF is not the same as CA (what you described). CA can cause a purple "fringe", but not all purple is PF. The difference is readily apparent on inspection. CA does not "bloom". PF does. As I noted above, PF is a digital-only phenomenon. Read any lens test from the "film era" and you will see no mention of PF.

See:
Chromatic aberration - Wikipedia, the free encyclopedia
Steve
I think you're fighting a losing battle there. If it is a fringe and it is purple, then I'm not going to argue that it is not *really* purple fringing because CCD sensors and blah blah blah -- because it literally is purple fringing. And of course it *is* more prevalent with some lenses than others, so it is also fair to name those lenses. If "digital only purple fringing" wants to be in a special category, it needs a new name...

01-05-2013, 01:51 PM   #24
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I know this is a bit off topic from the OP but,
I'm still confused by Purple Fringing vs. CA's.
All the examples of PF I've found in my photos could also be attributed to CAs.
What makes one PF and on CA?

To the OP,

I've looked though some of my digital images from my M100/2.8 and they look pretty clean.
01-05-2013, 02:56 PM   #25
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QuoteOriginally posted by stevebrot Quote
Lenses don't produce purple fringing, it is a digital sensor issue. It simply does not happen with color film. That being said, some lenses are more prone to encouraging the sensor to fringe. I can offer two Pentax-M lenses that I own that don't seem to be associated with that problem.
M 50/1.7
M 200/4

Steve




FWIW...I only own a few lenses that cause my K10D to fringe at all. Care to guess which ones?

PF has been documented numerous times during the film era.
01-05-2013, 03:05 PM   #26
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QuoteOriginally posted by Jonathan Mac Quote
The M85 doesn't so much purple-fringe as blue-fringe. 80% of it is gone by f/2.8 and I've never found it to be a problem. It's a beautiful lens.

I've never seen any really bad purple fringing in my images and I have a lot of Ms and I like to shoot with wide apertures.
My Kids are "Fridge Masters".
01-05-2013, 06:07 PM   #27
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QuoteOriginally posted by stevebrot Quote
Wrong...PF is not the same as CA (what you described). CA can cause a purple "fringe", but not all purple is PF. The difference is readily apparent on inspection. CA does not "bloom". PF does. As I noted above, PF is a digital-only phenomenon. Read any lens test from the "film era" and you will see no mention of PF.

See:
Chromatic aberration - Wikipedia, the free encyclopedia
Steve
wrong again steve. i never said pf was the same as ca. there are a number of factors that can contribute to pf, including ca. you're original claim that lenses don't cause pf is still wrong. they may not be the only cause, but they certainly can cause pf. even the wikipedia article you just linked to says so. you're right that ca doesn't cause "bloom", IF you mean sensor bloom. but the subject at hand is pf, so if by "bloom" you mean a bright purple halo effect evenly outlining objects on all sides, that can quite easily be caused by axial ca.
01-05-2013, 06:34 PM   #28
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QuoteOriginally posted by stevebrot Quote
sensors for adapted lenses. For example, does the FA 77/1.8 have PF on Canon APS or Canon FF?
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.
01-05-2013, 09:09 PM   #29
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QuoteOriginally posted by Swift1 Quote
What makes one PF and on CA?
CA is an established and well-known class of optical aberration. It is demonstrable and measurable on an optical bench and has a well-known and predictable presentation.

PF is a separate phenomenon that has a similar presentation to CA, but does not have the same behavior. There are those who would like to lump the two together, but they are not the same. But to my way of thinking that is like calling blood and ketchup the same because they are both red and stain clothes.


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01-05-2013, 09:14 PM   #30
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QuoteOriginally posted by tabl10s Quote
PF has been documented numerous times during the film era.
I was alive and shooting during the "film era" (started photography in 1969) and was ignorant about PF until I started shooting digital. Once I had a digicam (2002), it was pretty hard to ignore...a fairly constant presence on my Canon G2 and a pain in the rear and the topic of extensive discussion on most of the online photo forums at the time. There was no question at that time that the cause was in the cameras, not the optics.

That being said, there is no question that the optics are part of the equation. After all, we all know that some lenses are more prone to triggering PF than others. Why this is so has been widely discussed and I don't find many of the explanations compelling. I am fairly puzzled by one thing. If PF is caused by the lenses, why don't the lens makers make claims regarding the lack of PF in their new products?


Steve

Last edited by stevebrot; 01-05-2013 at 09:36 PM.
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