# Thin blue-ish outline around objects.. what is it? how to fix?



## chrisblau (Sep 20, 2009)

Hey all - I've just gotten into some more serious photography. I'm using a Canon XSi and an 18-200mm lens by Tamron (no IS, couldnt afford it). 

My problem is when I shoot (often outdoor shots) there is a thin blueish glow/outline around objects, often when the object is darker than the background.

What is it? Is it a symptom of a bad lens? Is there an easy way to take it out in post?

thanks much!

Chris


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## hulk (Sep 20, 2009)

Not sure, but it might be chromatic abberation.
Check out the pics in the article to compare.


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## Goontz (Sep 20, 2009)

Post some examples, it'll be easier for us to see what you're talking about and offer help.


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## musicaleCA (Sep 20, 2009)

Sounds exactly like chromatic aberration, and the lens you are using is prone to it. Avoid high-contrast situations, as CA is generated when an edge is extremely highly contrasting. CA can be removed in post, but it will always result in a loss of sharpness around these edges.


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## KmH (Sep 20, 2009)

It is a lens quality issue.

I think it's more commonly known as Purple-Fringing and it can be mitigated in post processing with Photoshop.

Google to find many, many tutorials out there about fixing it.


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## chrisblau (Sep 20, 2009)

Thank you all so much for the quick replies!

Yes - I do think its a CA problem. I did a quick search and found a short how to video about removing it, real straight forward stuff (especially if you're shooting in RAW). 



 is the link.

I'm a college kid so I didn't have a ton of money to spend on a lens and I wanted a lens that would give me a lot of possibilities (hence the 18-200). I'm thinking of getting a straight 50mm lens or something like that for indoor/museum use.. any suggestions? Minimum CA stuff, hopefully, and IS would be nice.. for a Canon body. 

Thanks again!


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## stierzy34 (Sep 20, 2009)

I'm in college too and know all too well about the money issues! I actually picked up a 50mm f1.8 for very cheap. I love it!


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## musicaleCA (Sep 21, 2009)

A 50mm prime doesn't really need IS. All of the ones in Canon's current line-up are very fast, an even on a crop body it's not a very long focal length to deal with.


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## Village Idiot (Sep 21, 2009)

KmH said:


> It is a lens quality issue.
> 
> I think it's more commonly known as Purple-Fringing and it can be mitigated in post processing with Photoshop.
> 
> Google to find many, many tutorials out there about fixing it.


 
Everyone I know commonly refers to it by CA, it's actual name.


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## musicaleCA (Sep 21, 2009)

Actually, purple fringing, while sometimes caused for the same reasons as CA, can also be caused by lens flare, and a score of other reasons. Purple fringing and CA are subtly different.


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