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01-09-2015, 03:13 PM   #16
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QuoteOriginally posted by btnapa Quote
I think PF is a function of the lens not the camera body.
Except that the phenomenon is entire absent from film photography. I have been shooting since the late 1960s and the first I heard of PF was when I bought my Canon G2 in 2002. At that time, it was considered to be a camera issue and was part of the test suite at most digital camera Web sites. That being said, it is true that some lenses are more prone than others.

Earlier sensor designs were prone to "bucket overflow" resulting in a purple bloom at the margins of bright areas. Current sensors are resistant to that problem, though some degree of PF is still present with many lenses. There has been some recent work that suggests that longitudinal CA in the UV range might be partially to blame with the purple artifact being due to scatter across the micro-lens array of the sensor. Apparently controlled testing with narrow bandwidth LED light sources results in PF only when UV light is part of the mix.


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01-09-2015, 06:11 PM   #17
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QuoteOriginally posted by stevebrot Quote
Except that the phenomenon is entire absent from film photography. I have been shooting since the late 1960s and the first I heard of PF was when I bought my Canon G2 in 2002. At that time, it was considered to be a camera issue and was part of the test suite at most digital camera Web sites. That being said, it is true that some lenses are more prone than others.
And yet I see it all the time, even in old magazines. I see it in every movie on TV from the 70s (and everything new too)...so was it always there, or is it in the video transfer?
01-09-2015, 06:59 PM   #18
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QuoteOriginally posted by vonBaloney Quote
And yet I see it all the time, even in old magazines. I see it in every movie on TV from the 70s (and everything new too)...so was it always there, or is it in the video transfer?
Huh? I personally tried to generate PF on film this last fall using my FA 77/1.8 on the Super Program with Ektar 100. I was fairly reliably able to do so on the K-3 using flash 2x overexposed wide open with crumpled aluminum foil as the subject, but was skunked on Ektar 100. LoCA was present with the characteristic near/far colors. PF, OTOH, was absent. Simply, PF is a product of digital imaging. That being said, you can get some pretty nasty fringing with certain lenses (usually wide angles) that have poor flatness of field. This causes severe LoCA at bright margins in the corners.*

As for the movies...I too see it all the time in direct video recording (digital or analog) meaning a huge amount of footage from the last two decades and maybe even further back. There might be issues with the video transfer as well. I have no idea how they do that


Steve

* A good example would be the F-Zuiko 35/2.8 on my Olympus XA. It is a fine optic, but can do strange things at the edges of the frame.
01-09-2015, 07:12 PM   #19
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QuoteOriginally posted by stevebrot Quote
Huh? I personally tried to generate PF on film this last fall using my FA 77/1.8 on the Super Program with Ektar 100. I was fairly reliably able to do so on the K-3 using flash 2x overexposed wide open with crumpled aluminum foil as the subject, but was skunked on Ektar 100. LoCA was present with the characteristic near/far colors. PF, OTOH, was absent. Simply, PF is a product of digital imaging. That being said, you can get some pretty nasty fringing with certain lenses (usually wide angles) that have poor flatness of field. This causes severe LoCA at bright margins in the corners.*

As for the movies...I too see it all the time in direct video recording (digital or analog) meaning a huge amount of footage from the last two decades and maybe even further back. There might be issues with the video transfer as well. I have no idea how they do that
Yeah, I don't remember ever seeing it in actual color prints I made myself (or even snapshots), but since becoming of aware of it, I do see it all the time. Maybe it is just lateral CA I've seen in prints and magazines, etc as that is quite common. But HD transfers of older movies I definitely see PF -- I was watching THE GAMBLER (the original with James Caan) just last week and noticed some. And in the usual places you'd get it too -- tree branches against sky, etc...

01-09-2015, 08:12 PM   #20
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QuoteOriginally posted by stevebrot Quote
longitudinal CA in the UV range might be partially to blame with the purple artifact
Interesting and I wonder if a UV or haze filter will reduce it? I see it mostly on thin tree branches in bright sun.

I read that filters were used by the pros in the film days (we all used them permanently on the lens too)
They were to prevent loss of contrast by the UV on the film.
Bell & Howell had a filter standard that a UV filter must not reduce a 100mm f/4 lens to below 100 lines/mm, and must not need refocus.
01-09-2015, 08:28 PM   #21
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QuoteOriginally posted by wombat2go Quote
Interesting and I wonder if a UV or haze filter will reduce it? I see it mostly on thin tree branches in bright sun.

I read that filters were used by the pros in the film days (we all used them permanently on the lens too)
They were to prevent loss of contrast by the UV on the film.
Bell & Howell had a filter standard that a UV filter must not reduce a 100mm f/4 lens to below 100 lines/mm, and must not need refocus.
It will more than likely make it worse. If it does make it better, it will be because of loss of resolution and contrast that goes with it. Although purple fringing can be prevalent on cheap, low-quality lenses, it also often goes hand-in-hand with the sharpest and most contrasty lenses (at least when wide-open) if they are not superbly corrected. (As noted above and often elsewhere, the FA77 fringes a lot, and it was just voted best lens ever on this forum.)
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