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Old Aug 13, 2009, 1:32 AM   #1
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Default Purple edges in d50 photos?

Noticed in most of the photos taken with d50 that there is a definite purple edge to most of the white areas especially if those areas meet a dark/black area. Is this a firmware issue or is there something else going on?
In the attached photo purple cast is noted on Rugby Jersey white areas and around the letters on the Jersey "SPRC"
Thanks for any help.

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Old Aug 13, 2009, 3:24 AM   #2
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You mean the Canon 50D right? (Not the Nikon D50.)

What you see is a type of chromatic aberration caused by different wavelengths/colours of light bending different amounts through a lens.

This is made worse by the fact that the shirt is out of focus and the light is very bright.

In general this is a property of the LENS you are using, not the camera, however...

It can be made worse or better by the processing engine that turns the RAW data from the sensor into a JPG file. I presume you are shooting in JPG mode.

I would suggest experimenting with different JPG processing modes, or better still by shooting in RAW mode and processing the images through a good RAW engine like DXOptics (which also corrects this sort of aberration very well).

So my suggestions to get rid of this if it bothers you:
1. Get the picture in focus.
2. Shoot RAW and use DXOOptics to process your pictures.
3. Get a better lens.
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Old Aug 13, 2009, 4:13 AM   #3
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Or you can get another camera...

peripatetic is correct purple fringing is characteristics of poor lens design; However some newer dSLRs have the chromatic aberration correction built-in to the body to work with cheaper lenses
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Old Aug 15, 2009, 5:15 PM   #4
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Thank you for the information....

So you all know, I did not choose this photo as an example of a "good" shot.... I know it's out of focus as well as it doesn't "show" anything worth looking at! LOL..

I chose this shot as a great illustration to the question I had regarding the purple fringe.

and yes, I did mean the Canon 50D....As my father uses Nikon...I sometimes make this error in my references to my canons.

I thank you both for your input. Yes, the lense used for this shot is not a very high end lense and yes, for the most part, I use the JPEG setting on the camera.

I will review other shots taken with better lenses (Canon 50mm and 85 mm) to see if I notice anything there.

Becky
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Old Aug 15, 2009, 5:23 PM   #5
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I believe a software update addresses this issue.
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Old Aug 16, 2009, 1:39 AM   #6
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Becky - what I meant is that the purple fringing is worse when the picture is out of focus, which is something you may not necessarily expect. :-)

It is one of the distinguishing features of more expensive lenses that they have coatings to reduce this kind of chromatic aberration as well as specially designed lens elements.
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Old Aug 16, 2009, 8:48 PM   #7
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Coatings don't reduce chromatic aberration in lenses.

The combination of flint and crown glass(the normal types of glasses used in regular lenses) reduce red/blue CA(achromatic doublet), while additional low dispersion (ED, LD, SD, etc) glass reduces CA in the green region as well, and are known as APO lenses. (Apochromatic)

Last edited by dnas; Aug 16, 2009 at 9:00 PM.
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Old Aug 16, 2009, 9:39 PM   #8
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I used this same lense on the less expensive 300D before it died and I never noticed this problem.

I'm sure there's a reasonable explanation for the difference showing so distinctly from each model of camera.... right?

Also is this something that an filter may possibly correct or decrease?

Becky
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Old Aug 16, 2009, 10:27 PM   #9
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The interface between black and very white will show this problem the most. If you never took shots to highlight this, you may never have noticed it before.

A filter will not help, if you wish to maintain the proper colour balance.

You can correct this problem in Photoshop.
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Old Aug 17, 2009, 3:55 PM   #10
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Update the firmware on your 50D and see if this helps..
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