Purple Outline

[Rassy7]

Hi, I have been shooting some military aircraft and am running into a problem. I get this purple edging outlining the aircraft which becomes overbearing when zoomed in or cropping. It seems to be the worst when the aircraft and the beckground (clouds) are both gray. It's not too bad or not there at all when it's blue sky or when the aircraft is a different color. I'd like to at least know what it causing it so I know how to avoid it if I can't fix it. Thought someone else might have run into this problem and could provide some insight. I inserted an example in regular view as well as zoomed in.

Thanks,
Josh

[hotreds]

R U using a UV filter?

[Rassy7]

Yes. Just a standard Tiffen UV filter.

[hotreds]

Hmmm- has your monitor been calibrated? Do you use any special settings on your camera- what camera are you using? Digital magnification?

[Rassy7]

No digital mag, camera body: Canon 20d, Lens: 75-300, settings pretty consistent with usual: ISO: 100, f5.6, shutter speed: don't remember exaclty but somewhere around 1/1000.

[bcradio]

Looks like a case of chromatic abberation...

http://en.wikipedia.org/wiki/Chromatic_aberration
http://www.photos-of-the-year.com/articles/adobe-raw/

[ironfan]

Exactly what it is, Chromatic Aberation.

Those screen shots look like they were taken in Lightroom so go to the Develop module and open the details tab on the right hand side and you can try to correct it.

[Rassy7]

Perfect. Thanks a bunch hotreds, bcradion and ironfan! I knew I could get this mystery settled once and for all here 

Josh

[hotreds]

Kewl- looks like you should be able to fix w/o too much trouble!

[Rassy7]

Ya, bcradio's links were both great. The wiki has a few graphics that make it easy to understand and the article explains how to fix it. I'm sure I can at least make it less obvious now pretty easily.

ironfan, I like your profile pic.

[tbunce]

Since you are also shooting RAW, the latest version of Canon's Digital Photo Professional has added RAW processing highlight and shadow to the already really nice chromatic aberration and color blur corrections. The version released some time late last year added a lot of lenses to their database, including the one you have (the same as what I used to use before I got a 70-200 f4 L.) I think the color blur feature should help that a lot also because of the high contrast between the sky and aircraft. I've seen that as a red glow even with my L lens when shooting sunrises behind an aircraft.

I've been using DPP pretty exclusively for exposure and color correction and really like how much I can do with it before converting to TIFF for the occasional tweak in Photoshop. It's actually critical for me and my stitching because all the RAW processing controls are totally consistent regardless of how much bright sky or dark airplane is in my field of view, unlike Photoshop's RAW processing.

Just be aware the "Brightness" control is actually Exposure. The brightness control is in the histogram as a sliding line on the right edge of the view box. Black point is on the left.

Good luck. Let's see the after processing image!