----- Original Message ----
From: norman <[EMAIL PROTECTED]>
To: gimp-user@lists.XCF.Berkeley.EDU
Sent: Tuesday, March 18, 2008 8:52:22 AM
Subject: Re: [Gimp-user] chromatic aberration

< snip >
> Unfortunately, ca is controlled in lense manufacture and design and
> has two solutions, software or better glass.  Minimizing ca via
> technique would severly limit your scope, imo.

I would expect most lenses these days to be made such that they do not
cause CA. From what I have read, there is another factor to be taken
into account, the chip responsible for recording the image. I gathered
that small chips are quite prone to CA and the larger the chip the lower
the CA and that it virtually disappears in the 1:1 (35 mm) format. The
camera I am using is an upper end, point and press so perhaps I need a
better camera with a larger chip.


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.

Software can certainly help with this, and "that other product" has this built 
in. Then again, you can buy a couple of really nice lenses for the price you'll 
pay for that product ;>

Meanwhile, you're more likely to have trouble because of poor focus, camera 
shake, and other more mundane issues, than you are from CA in general. I'd say 
just forget about it, and focus (sorry ;) on your artistic abilities. Let's 
face it, the lenses that most of the "greats" used were total junk compared to 
the most basic point and shoot now. See Ken Rockwell's comments on "it's not 
the camera" at http://www.kenrockwell.com/tech/notcamera.htm


"You can tell whether a man is clever by his answers. You can tell whether a 
man is wise by his questions." — Naguib Mahfouz

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