----- Original Message ----
From: norman <[EMAIL PROTECTED]>
> CA is indeed a function of the lens quality. You're also right that a smaller 
> sensor makes CA more visible, that's just simple geometry. If the lens 
> produces an abberation of any given size, then if the sensor is half the 
> size, the apparent effect of the abberation is doubled.
> Unfortunately, only the best lenses have this effect almost entirely 
> eliminated. You'll find some that are called "Apochromatic" or just "Apo". 
> They tend to be much more expensive than "normal" lenses (typically called 
> "achromatic"). I have a perfectly respectable, but low-end, Nikon zoom lens 
> designed originally for film use that generates what to me is an entirely 
> unacceptable amount of CA at the long end of its zoom on my DX-format D-SLR.

I feel sure that you must be correct. I have never seen any noticeable
fringing or CA effects with my ordinary photography it is only with this
project I set myself of copying a lot of old colour transparencies. In
the old days I used to often feel frustrated at not being able to do a
great deal with colour slides such as I did in my darkroom with black
and white film. Thus, I saw this as chance to catch up on history and at
the same time, maybe, produce some interesting images digitally. It now
looks as though I shall be frustrated yet again.



Are you "copying" the slides, or are you scanning them?

If you're using a slide copying attachment and effectively rephotographing them 
onto your digital camera, then the CA of the copying equipment will be a 
factor. On the other hand, if you're scanning them, then CA isn't usually an 
issue, because scanning is a different mechanism entirely. If you're scanning 
and then seeing CA, I believe the CA must be in the original slide. Perhaps you 
just didn't notice before? We do tend to view digital images at much higher 
magnifications than we used to view silver halide images. (To be fair, that 
might not be true of slides though!)


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