06-15-2011, 06:17 PM
There are actually 3 types of aberrations in this picture.
1) PF. Those are the violet, bright purple haloes around the overexposed highlights on the metal parts of the instrument. In principle, this is not really true Chromatic Aberration, it is a mix of things, very likely, although it normally only happens at large apertures, and is much more distinct with digital than with film, so there likely is a sensor or sensor circuitry element involved as well. Generally, these can't be undone, because information is lost. This seems, effectively anyway, to be a weird overexposure effect. PF can occur in and out of the focus zone, but is most clear in and close to the focus zone.
2) Spherochromatism, also called longitudinal chromatic aberrations, or LoCA. These only occour in out of focus area, generally reddish in front of the focused area, and greenish behind the focused area, wherever there are very hard contrast transitions. In the picture you can see this in the background, at the transition of the grey and white parts, and on the instrument itself, but those are only tiny patches, and they also overlap partly with the PF. It's best seen almost at the bottom of the photograph, in the centre almost, where just above a darkish part you can see a reddish edge overlayed on the gold colour of the instrument, which towards the left and top mixes with PF. LoCA can be corrected, but it is a lot of work to do manually, as you need to do a lot of masking, layering, and colour corrections. There is a piece of software nowadays, which can handle LoCa, but I can't remember which it is now. LoCa is caused by residual spherical aberrations, hence the official term of Spherochromatism, which term these days almost nobody seems to use anymore. As indicated, this can be corrected by very good (super)apochromatic designs and to a large degree by aspherical elements (although those are normally really best at or around a specific aperture). However, aporchromatic lenses normally have relatively small apertures, and therefore suffer less from spherical aberrations in the first place. These spherical aberrations at large apertures also provide good bokeh, generally speaking, so from that POV it is a good and a bad thing at the same time.
3) Latitudinal Chromatic Aberrations (blue and yellow most often), which also occur in hard contrast transitions, essentially the blue parts in nose and the upper part of the instrument. Some PF is mixed in here as well. LCAs normally occur in in-focus areas. These can also be corrected to a large degree - most software can handle this automatically these days, although this is a rather severe case of these aberrations (plus some PF mixed in). There is quite a large transitional zone here with PF too.
I'd suggest that if this bothers you really a lot, you better convert this to B&W if you want to get a reasonable picture. That's aso the fastest way of dealing with these problems. See here, just a simple conversion (10 seconds of work):
[ATTACHMENT NOT FOUND]
HTH, kind regards, Wim
1) PF. Those are the violet, bright purple haloes around the overexposed highlights on the metal parts of the instrument. In principle, this is not really true Chromatic Aberration, it is a mix of things, very likely, although it normally only happens at large apertures, and is much more distinct with digital than with film, so there likely is a sensor or sensor circuitry element involved as well. Generally, these can't be undone, because information is lost. This seems, effectively anyway, to be a weird overexposure effect. PF can occur in and out of the focus zone, but is most clear in and close to the focus zone.
2) Spherochromatism, also called longitudinal chromatic aberrations, or LoCA. These only occour in out of focus area, generally reddish in front of the focused area, and greenish behind the focused area, wherever there are very hard contrast transitions. In the picture you can see this in the background, at the transition of the grey and white parts, and on the instrument itself, but those are only tiny patches, and they also overlap partly with the PF. It's best seen almost at the bottom of the photograph, in the centre almost, where just above a darkish part you can see a reddish edge overlayed on the gold colour of the instrument, which towards the left and top mixes with PF. LoCA can be corrected, but it is a lot of work to do manually, as you need to do a lot of masking, layering, and colour corrections. There is a piece of software nowadays, which can handle LoCa, but I can't remember which it is now. LoCa is caused by residual spherical aberrations, hence the official term of Spherochromatism, which term these days almost nobody seems to use anymore. As indicated, this can be corrected by very good (super)apochromatic designs and to a large degree by aspherical elements (although those are normally really best at or around a specific aperture). However, aporchromatic lenses normally have relatively small apertures, and therefore suffer less from spherical aberrations in the first place. These spherical aberrations at large apertures also provide good bokeh, generally speaking, so from that POV it is a good and a bad thing at the same time.
3) Latitudinal Chromatic Aberrations (blue and yellow most often), which also occur in hard contrast transitions, essentially the blue parts in nose and the upper part of the instrument. Some PF is mixed in here as well. LCAs normally occur in in-focus areas. These can also be corrected to a large degree - most software can handle this automatically these days, although this is a rather severe case of these aberrations (plus some PF mixed in). There is quite a large transitional zone here with PF too.
I'd suggest that if this bothers you really a lot, you better convert this to B&W if you want to get a reasonable picture. That's aso the fastest way of dealing with these problems. See here, just a simple conversion (10 seconds of work):
[ATTACHMENT NOT FOUND]
HTH, 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 ....