On Tue, 2008-03-18 at 08:13 -0700, Simon Roberts wrote:
> ----- 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
> Cheers,
> Simon
> "You can tell whether a man is clever by his answers. You can tell whether a 
> man is wise by his questions." — Naguib Mahfouz

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.


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