05-18-2012, 08:36 PM
[quote name='Klaus' timestamp='1337362560' post='18286']
The origins of purple fringing are not really clear - at least to me. The best guess is a blooming effect by the micro lenses on the photodiodes - and all sensors have them.
[/quote]
If I may expand on this:
PF also occurred in the film era, although generally not as pronounced and certainly in B&W not as obvious, but always as either purple fringes/haloes at high contrast transitions in colour, or intermediate grey tone haloes/fringes in B&W.
It only occurs at large apertures, and not with all lenses, but mostty large aperture lenses. Because it is stronger in digital, one can indeed not help but think some blooming effect aiding in the creation of this deect, but as this also occurred with film, something else must contribute to its creation as well. Since PF can occur anywhere in a picture, just as strong in back and foreground or centre and edges, in combination with the fact that it may surround an object fully provided its edge is a high contrast edge, it can not be CA, as there is no specific tangential or sagittal relation. Neither does it get worse towards the edges, thereby excluding general optical flaws. It does get less when stopping down, to the point of disappearing at smaller apertures, so therefore it does seem lens related in some way.
IOW, there appears to be both a lens related component and a sensor or medium related component at play.
There has always been a fair amount of speculation on the cause of PF, but so far no one has offered a proper scientific explanation, not to my knowledge anyway.
Kind regards, Wim
The origins of purple fringing are not really clear - at least to me. The best guess is a blooming effect by the micro lenses on the photodiodes - and all sensors have them.
[/quote]
If I may expand on this:
PF also occurred in the film era, although generally not as pronounced and certainly in B&W not as obvious, but always as either purple fringes/haloes at high contrast transitions in colour, or intermediate grey tone haloes/fringes in B&W.
It only occurs at large apertures, and not with all lenses, but mostty large aperture lenses. Because it is stronger in digital, one can indeed not help but think some blooming effect aiding in the creation of this deect, but as this also occurred with film, something else must contribute to its creation as well. Since PF can occur anywhere in a picture, just as strong in back and foreground or centre and edges, in combination with the fact that it may surround an object fully provided its edge is a high contrast edge, it can not be CA, as there is no specific tangential or sagittal relation. Neither does it get worse towards the edges, thereby excluding general optical flaws. It does get less when stopping down, to the point of disappearing at smaller apertures, so therefore it does seem lens related in some way.
IOW, there appears to be both a lens related component and a sensor or medium related component at play.
There has always been a fair amount of speculation on the cause of PF, but so far no one has offered a proper scientific explanation, not to my knowledge anyway.
Kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....