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. Norman _______________________________________________ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user