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Purple Branches

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jimva
 
Posts: 26

Purple Branches

Post Wed Jan 20, 2010 11:45 pm


Image

Is the camera overexposing the sky causing the purple branchs? Used middle of the road lens at best.
Why are branches purple?

dougj
 
Posts: 2276

Re: Purple Branches

Post Thu Jan 21, 2010 1:45 am


That looks like lateral chromatic aberration, usually caused by the lens and a strong backlit subject, different colors are incorrectly separated and focused at different positions on the sensor. CA is a characteristic of the lens, and the ability to suppress it varies between lenses, some manufacturers use optical glass formulated specifically to reduce this in some of their lenses. Some image processing software include the ability to correct lens aberrations, CA is one of these corrections.

jimva
 
Posts: 26

Re: Purple Branches

Post Thu Jan 21, 2010 3:03 am


Doug,

Thank you very much for your input ino this problem. I had never seen CA before this and will work to prevent it in the future.
Best regaurds and THANK YOU!

Jim

dougj
 
Posts: 2276

Re: Purple Branches

Post Thu Jan 21, 2010 3:40 am


Glad I could help Jim, there is a lot on the web about CA, and the different types, as it's fairly common. This characteristic is sometimes measured, or at least discussed, as part of a lens review. I think you're a Nikon shooter, so here are examples of 2 lenses - one a low cost 18-55mm and the the Nikkor 14-24mm. Completely different lenses in all respects, but interesting at least to see the comparison, the CA measurements are on page 2.

http://www.photozone.de/nikon--nikkor-a ... est-report

Your image processing software may have an option to correct some or all of it, Photoshop has this built in both in the RAW converter and the main program.


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