12-03-2010, 04:10 AM
[quote name='wim' timestamp='1291334181' post='4720']
One thing that is interesting however is that PF or purple fringing, which is an aberration oftentimes considered to be CA (which it isn't by the definition of CA, because it isn't sagittal or transversal in nature), is much stronger than it is with film, and always disappears when stopping down a few stops. Now, this could either be caused by someting to do with the sensor assembly itself and extremely high contrast transitions, the A/D processing, both of these, or generally indeed by anything that causes an increase in contrast due to signal amplication, whether optical or electrical/digital and the signal clipping in a weird way.[/quote]
PF is a really weird thing... it's both lens and sensor related. I say lens related because well-corrected lenses (e.g. 125 f/2.5 APO-Lanthar, 200 f2L IS, 200/4 Micro-Nikkor and I'm sure the 60 f/4 UV-VIS-IR too) don't show it. But it is also a sensor related thing because lenses like the 85 1.2L wide open [url="http://www.flickr.com/photos/genotypewriter/4635819634"]show it on digital[/url] but [url="http://www.flickr.com/photos/genotypewriter/4495611132/"]not on film[/url].
I think calling it CA is fairly wrong because CA is caused by refraction of light of different wavelengths. But when light is passing through the center of a lens, there's no refraction so there can't be CA but you can often see [url="http://www.flickr.com/photos/genotypewriter/4635819634/sizes/o"]PF in the center[/url]. Similarly I haven't seen PF getting worse towards the corners like CA typically does.
[quote name='wim' timestamp='1291334181' post='4720']
As BC and GTW indicate, all of this could actually be tested quite easily, by breaking the contacts between lens and camera and just shooting at maximum aperture. I guess I may give this a try myself, too <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />.
[/quote]
I just did earlier this morning before turning up to work... hmm the early findings are a bit shocking and not in favour of us DxO-skeptics <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/sad.gif' class='bbc_emoticon' alt='
' /> I'm going to do a thorough test and upload an article within the next few days, hopefully.
GTW
One thing that is interesting however is that PF or purple fringing, which is an aberration oftentimes considered to be CA (which it isn't by the definition of CA, because it isn't sagittal or transversal in nature), is much stronger than it is with film, and always disappears when stopping down a few stops. Now, this could either be caused by someting to do with the sensor assembly itself and extremely high contrast transitions, the A/D processing, both of these, or generally indeed by anything that causes an increase in contrast due to signal amplication, whether optical or electrical/digital and the signal clipping in a weird way.[/quote]
PF is a really weird thing... it's both lens and sensor related. I say lens related because well-corrected lenses (e.g. 125 f/2.5 APO-Lanthar, 200 f2L IS, 200/4 Micro-Nikkor and I'm sure the 60 f/4 UV-VIS-IR too) don't show it. But it is also a sensor related thing because lenses like the 85 1.2L wide open [url="http://www.flickr.com/photos/genotypewriter/4635819634"]show it on digital[/url] but [url="http://www.flickr.com/photos/genotypewriter/4495611132/"]not on film[/url].
I think calling it CA is fairly wrong because CA is caused by refraction of light of different wavelengths. But when light is passing through the center of a lens, there's no refraction so there can't be CA but you can often see [url="http://www.flickr.com/photos/genotypewriter/4635819634/sizes/o"]PF in the center[/url]. Similarly I haven't seen PF getting worse towards the corners like CA typically does.
[quote name='wim' timestamp='1291334181' post='4720']
As BC and GTW indicate, all of this could actually be tested quite easily, by breaking the contacts between lens and camera and just shooting at maximum aperture. I guess I may give this a try myself, too <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />.[/quote]
I just did earlier this morning before turning up to work... hmm the early findings are a bit shocking and not in favour of us DxO-skeptics <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/sad.gif' class='bbc_emoticon' alt='
' /> I'm going to do a thorough test and upload an article within the next few days, hopefully.GTW