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12-21-2008, 10:24 AM   #1
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Still Fringing on my Sigma

Flickr Photo Download: FRING TEST

So i exchanged my first copy because of its softness along the edges of pictures, and now i have this. Finging on ANY highlights that aren't in the relative center of the image, this is just a small example. Iif i take a picture of something that's shiny and has a bit of reflection, and is even somewhat close to the edge of the frame, BOOM violet/yellow fringing.

I don't even want to go back to Henry's, i want to send this in directly to Sigma.

Any suggestions?

12-21-2008, 12:50 PM   #2
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Original Poster
*desperate bump*

EDIT: Can this potentially be a problem with the camera itself, not the lens?
12-21-2008, 01:05 PM   #3
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Hi PNTXFTW,

First, it's usually helpful if you state your body model and the specific lens. I'll assume from the exif that you have the K200 and Sigma 17-70. If this is indeed the lens you are talking about, I have one, and it fringes, though I think it controls this pretty well for the class of lens, and its price.

Most zooms will have some fringing or CA at the edges. If you're looking for an example with no such abberations, especially shooting the lens wide open, then I think that you'll be sorely disappointed. Some lens models just fringe more than others. If you want lenses that control these abberations better, then look at the premium lens offerings from the different manufacturers, and concentrate on the primes, but even in these, you'll usually find some circumstances where they exhibit fringing, and most don't suffer from the design compromises necessary in a zoom.

Generous use of low dispersion glass elements (called "ED" [Extra low Dispersion] by Pentax, "SLD" [Super Low Dispersion] or "APO" [apochromatic] by Sigma, "LD" [Low Dispersion]by Tamron, and "SD" [Super low Dispersion] by Tokina) in the optical design will help correct abberations, but realize that this glass is expensive, and will be directly reflected in the price of the lens. Also realize that most lens designs will have some built-in compromises (many for cost of mfg), so are not really going to be "perfect" (Leica owners will probably disagree to some extent, but they're. . . Leica owners ) )

Another factor in CA, though many will probably disagree, is the sensor, IMO. My K10 exhibits more CA and PF than either my DS or my K20 using the same lenses in the same situations.
Since your K200 uses essentially the same Sony CCD sensor, I'll assume that this increases the propensity to show fringe to some degree.

Try stopping down a stop or two, if you're shooting Jpeg. This should help with bringing up the sharpness at the edges which should reduce the fringing. Check into the CA correction tools available in your editing software. It's really pretty fast and easy to correct for. Many find selective desaturation to be effective. Personally, I choose to use color mode cloning in PSP, but that's me. . .
Try RAW with a converter that has some kind of CA correction included in the conversion processing.

Bottom line, IMO -- Don't obsess about the CA and PF, as long as it isn't excessive for the particular lens model (read some online lens reviews for your model). Take some pics, process the good ones developing an acceptable workflow to eliminate the fringing, and have some fun with your camera.

If it's any consolation, I recently obtained a Sigma EX 300 f2.8 APO (over $3K USD lens new), and although it fringes less than my Tamron SP 300 f2.8, it still exhibits fringing. Am I happy with it? -- you bet!

Scott
12-21-2008, 07:05 PM   #4
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ya i guess i'm over analyzing a bit

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