Blue circles around coin edges

dc_dweller

New Member
The following two images of a coin have annoying blue edges. I was wondering if someone can explain how to get rid of them.

The picture was taken with a D70, a 70-300 lens and a 12mm extension tube. A glass-top coffee table was used. A 26 Watt daylight fluorecent bulb was lit underneath the glasstop, and a piece of regular sheet of white paper was placed on top of the glasstop. A 3-inch cylinder was placed on top of the paper sheet and finally the coin was mounted on top of the cylinder. The coin was lit with another 26 Watt daylight bulb screwed into a regular desk l&.

The camera was calibrated for White Balance. Another photo was taken with WB simly set to "daylight" and it had the same effect - a blue edge.

Thanks in advance to anyone who has some ideas about this annoying artifact.

 

vmckenzie

New Member
I don't have an answer to your post...I am interested in doing some macro photography with
my D70...I have the lens that came with it and also a 70-300mm lens...what exactly is the 12mm
extension tube? Thanks Vic
 

cuti_95

New Member
well,
I never use such techniques and dont know how strong is the light you had. However what I saw and hear from you suggest that lack of light is the major cause.
As you said you had only two sources of light and looking at the coin, but only one main source provide light to the subject. the angle of light is from the top right corner (see the reflection on the forehead, chin and the top right part of the left image). Your now see more blue on the low edge of the coin, where the coin received least light. more obvious on the coin on the left side, there is almost no blue edge on the top right edge where the light was directing on

about the blue color, my best guess is it is the effect resulted from a combination of low light, fluorecent light you had, and the way the CCD/CMOS reacts to the low light.

overall, my suggestion is to get more light sources and stronger light and avoid using fluoresent lights.

WB setting could also make the picture blue-er or red-er.

Cuti
 

narsuitus

Active Member
Based on what I see and what you describe, it looks like an optical defect called "chromatic aberration." Try a Google search for more information and possible solutions.
 

narsuitus

Active Member
Be thankful that you were using a telephoto because chromatic aberrations are even worse when shooting close-ups with a wide-angle lens.

Stopping the lens down (using f/16 instead of f/4) may help reduce the chromatic aberrations.

Using a single focal length (prime) macro lens instead of a zoom may help reduce the chromatic aberrations.
 
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