Alan Chan http://www.pbase.com/wlachan
Mast all wide angle lenses exhibit some CA, the problem with digicams is a
little more complex, sensors have two characteristics that are very different
from film. Firstly for all intents you can consider film to have no depth,
light that strikes it at an acute angle will be recorded pretty accurately,
with sensors that have micro-lenses which are position above the actual light
sensitive substrate. So this means that acute light angles are going to cause
all sorts of problems such as vignetting and spill to adjacent sensor sites.
Secondly unlike film the majority of sensors measure the primary colours in
slightly different positions, these measurements are then used to approximate
the colour that would likely have been at the actual pixel site. As you can
imagine this approach can be easily derailed and the colour separation caused
by CA is something it doesn't handle well, in fact most demosaicing algorithms
tend to magnify the effect in the final image.
These are just some of the limitations we have to deal with using the current
technology, digital image capture is no panacea but it does have a lot of
positive aspects too of course :-)
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