[Gimp-user] chromatic aberration

[norman]

On Tue, 2008-03-18 at 08:13 -0700, Simon Roberts wrote:
> 
> ----- Original Message ----
> From: norman <norman at littletank.org>
> To: gimp-user at 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.

Norman