[wim]

[quote name='Lomskij' timestamp='1291557085' post='4771']

Ok, let me quote that again:



"As the human eye and autofocus systems are particularly sensitive to green light, both manual focus and autofocus tend to bring the green image in sharp focus. The other colors of the spectrum are left defocused and add up to a magenta fringe. For this reason purple fringing is more common than green fringing."



To me it clearly says that PF is LoCA - just in this case you get purple fringing only, without its green counterpart.

[/quote]

Even toothwalker can be wrong. And we're talking optical systems of the non-living kind here.



The problem with what we call PF rather than any of the chromatic aberrations or CA like lateral chromatic aberrations or LA, LoCa, spherochromatism or longitudinal chromatic aberrations, is that due to the fact that it actually isn't a proper chromatic aberration, it can coincide with chromatic aberrations. One of the differences between LoCa, and even lateral chromatic aberrations, is that these only occur on one side of the contrast transition. PF may occur everwhere surrounding the contrast transition, plus it may occur everywhere in the image, in focus, out of focus, and anywhere from the centre to the extreme corners, whereas proper chromatic aberrations do not occur in the centre of an image, generally speaking, and LoCA=a only occurs in the OOF area of an image.



In short, chromatic aberrations have a spherical component, PF doesn't. That is the big difference.



As to exact colours: that is always hard, because colour hue and colour intensity depends on processing a lot, but also on the lenses and camera used. Generally speaking, PF is bright purple, but may be a bit more bluish, LoCa generally varies from dark red, almost brownish red, to magenta in the foreground and cyan to dark green in the background, and lateral chromatic aberrations vary from dark to bright blue to purplish blue on the inside of high contrast transitions (cente of image side) and green to green yellow to bright yellow to burnt orange on the outside of high contrast transitions (away from the centre of the image).



There is a very good example of PF in the 50L APS-C review:



As is quite clear, PF often encircles the high contrast transitions, and it occurs both in OOF and in fous areas, and it occurs from the centre to the extreme corner.



LoCa, Spherochromatism, or longitudinal aberrations:



85L FF LoCa from this site. BTW, in the 85L II FF test you can also see PF in the bokeh picture around the nose of the statue, which is in focus, around the highlights in the Christmas decorations (?) towards the bottom (OOF), and also around the eye and eye brow of the statue (OOF). Here is that picture, which also shows LoCa of course:



And here is a detail of the statue, which shows PF more clearly:



Note that because the nose is sharp, this cannot be bokeh fringing, LoCa, or whatever you want to call it, but only PF.



Lateral chromatic aberrations, also from this site:



The inside blue and outside yellow aberrations are clearly visible. This is from a Nikon lens, but I can't remember which one.



Another good example, but with quite different colours, is this:



From the Tokina 11-16 review here on Photozone. You can see that dark blue to purplish blue alternates with green, depending on whether it occurs on the outside or inside edge, relative to the centre of the image.



In short, just based on colour one can't decide which aberration we are dealing with, one also has to examine the actual characteristics.



For proper PF it still stands that it has a non-spherical component, and that it occurs all over the picture, and may encircle high contrast transitions completely in a single colour, single fringe, which makes for the big difference with proper chromatic aberrations, be it lateral or longitudinal.



HTH, kind regards, Wim