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Old Sep 12, 2006, 8:47 AM   #1
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Can anyone tell me why there is a red fringe at the lower edge of this shot? It was taken just after moonrise, with the moon partially eclipsed. The camera was a DS, with a Sigma 170-500mm lens at 500mm, exposure 1/6th of a second at f9, ISO 200, tripod mounted. It was shot RAW, then converted to JPEG by Pentax Photolab. Other than cropping, no other processing.

AK
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Old Sep 12, 2006, 9:00 AM   #2
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Probably something to do with the lens itself.... or perhaps atmospehric affect.
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Old Sep 12, 2006, 4:24 PM   #3
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Hi AK,

Looks like CA (chromatic aberration), pretty common on moon shots because of the high contrast. Stopping down more can sometimes reduce it further. as will getting the sharpest focus possible. It's caused by different colors being refracted at different rates by the glass in the lens elements. If not CA, then it's blooming where the built up electrical charge in some pixels overflows to surrounding pixels. Sometimes it's hard to tell which is the cause. One way to cure it is in PP, desaturating the moon to B&W if you want to keep the sky color, or shooting in B&W.

Scott
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Old Sep 12, 2006, 4:27 PM   #4
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whatever it is, i can tell you how to remove it..
what programs do you have??

i lied. it affects too much of the overall image..

roy
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Old Sep 12, 2006, 5:01 PM   #5
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I imagine there is nothing wrong with the picture and that is how it actually looked! When the moon, or sun, is close to the horizon the light at the bottom of the object passes through a lot more atmosphere and various refractive effects come into play.



Incidently, these effects are great enough that they must be accounted for when doing sextant navigation.
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Old Sep 12, 2006, 5:09 PM   #6
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john,
do we have another sailor onboard(pun intended)??

roy
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Old Sep 12, 2006, 11:42 PM   #7
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Ahoy Roy, crossed the Pacific a long time ago on a 32footer.

We had a radio, Seiko watch, plastic sextant and a set of 249 (?) tables. Heck we even found where we were expecting to go! Hardly been onboard since then.
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