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02-18-2007, 09:15 AM   #1
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Whats the blue line around objects?

What exactly is the blue line around some of the objects in my 2nd picture? Is it called vingetting (sp?)?
First pic is tiger taken with k10d sigma 70-200mm f2.8 lens.
Second is gx-1l with 200mm f3.5 revue lens.
Is this problem caused by camera, lens, poor quality of lens. Thanks



02-18-2007, 09:27 AM   #2
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Blue Lines around some object...

It is called Chromatic Aberrations.

Here is an explanation on why it happens.

"In optics, chromatic aberration is caused by a lens having a different refractive index for different wavelengths of light (the dispersion of the lens). The term "purple fringing" is commonly used in photography, although not all purple fringing can be attributed to chromatic aberration."

It usually happens in cheaper lenses.

If you shoot Raw you can reduce it in Adobe Camera Raw. It is under the lens tab.

Hope this helps

Doug
02-18-2007, 10:50 AM   #3
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Original Poster
Thanks alot. Very informative explanation. I've taken alot of other photos with that lens and it has not had the "purple fringe". Maybe the bright snow caused it? For the price I cant complain , it was relatively cheap. Thanks again.
02-18-2007, 11:57 AM   #4
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QuoteOriginally posted by reknelb Quote
Thanks alot. Very informative explanation. I've taken alot of other photos with that lens and it has not had the "purple fringe". Maybe the bright snow caused it? For the price I cant complain , it was relatively cheap. Thanks again.
Yes, the bright snow has a great deal to do with it. You frequently see CA (chromatic aberration) when there is a juxtaposition of bright and dark. A good example is tree branches against the sky.

NaCl(even good lenses can exhibit it in some circumstances)H2O

02-18-2007, 01:05 PM   #5
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reknelb,
it's fairly easy to get rid of it in PPing with just about any decent graphics program.
02-18-2007, 08:18 PM   #6
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Just curious because I noticed something in the photos here.

The second shot, when compared to the first shot, the snow has this very faint bluish cast to it. but the other colours appear to be dead on. Is this caused by CA or something else? What would that term be if it was something else?

Thanks.
02-19-2007, 03:02 AM   #7
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Hi Alvin

QuoteOriginally posted by Alvin Quote
Just curious because I noticed something in the photos here.

The second shot, when compared to the first shot, the snow has this very faint bluish cast to it. but the other colours appear to be dead on. Is this caused by CA or something else? What would that term be if it was something else?

Thanks.
I might be wrong here but I think that's caused by white balance being set too cold so you get a blue-ish tint to your photos. Please feel free to correct me if I am wrong, everyone!

cheers
Kenny
02-19-2007, 07:33 AM   #8
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QuoteOriginally posted by kjao Quote
Hi Alvin



I might be wrong here but I think that's caused by white balance being set too cold so you get a blue-ish tint to your photos. Please feel free to correct me if I am wrong, everyone!

cheers
Kenny


not blue enough..I think...

it would look ore like this



he wouldve noticed it too if it the wb was too cold...

02-19-2007, 08:13 AM   #9
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To directly answer your question, yes, it's the lens that causes the CA. Cheaper lenses also contribute to things like image distortions, and areas where the color might not match the surrounding colors in the same object. The 18-55 kit lens, for example, is not the best quality... It has some bad vingiette at the wider angles, of course, it's great quality when you consider it costs less than a hundred bucks.

The bad part is, the lenses never tell you about these "features" until it's too late in most cases. For example, I was about to hit the "purchase" button on a sigma wide angle some time ago, but decided to do some searching first... Glad I did... Turns out that lens is famous for distortion, which I really don't want in my wide-angle shots!

Now, the interesting part about using a digital SLR, and a lens with these issues, is that, as others have mentioned, there are digital ways to fix all of these problems with a bit of work.
02-20-2007, 07:50 PM   #10
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Haha yes! So I'm not the only one in here with a GX-1L!
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