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Old May 19, 2006, 5:05 PM   #1
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Join Date: May 2006
Posts: 6

During my s5600 review search I came across this sample:


Is it normal- under those circumstances- that blueish contour on the sky border?


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Old May 19, 2006, 8:54 PM   #2
Join Date: Jun 2003
Location: Savannah, GA (USA)
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You'll see this issue referred to as Purple Fringing (a.k.a, PF). You'll also see it referred to as CA (Chromatic Aberrations). Neither term is exactly correct.

I can remember reading some comments about it trying to figure out where it came from years ago, since traditional Chromatic Aberration caused by lens deficiencies is not purple only like that. I even went to the trouble of buying hot mirror filters (designed to block Infrared light) to see if that would help. I wasted my money. lol

A Senior Kodak Engineer once commented that it's mostly caused by refraction of light by the microlenses used in most sensors. Each photosite has a tiny pillow shaped microlens over it to help amplify the light reaching it (with millions of them in a typical digital camera sensor).

Purple fringing tends to occur in high contrast areas with a lot of difference in brightness (for example, tree limbs against a white sky), most often at wider apertures (lower f/stop numbers). Another factor is CCD Blooming (where the charge from one photosite overflows to another). But, light refraction is likely the biggest cause.

Lens quality also impacts it, as does the size of the sensor and it's photosites (it's tough to focus light at the correct angles using a tiny sensor with millions of photosites without some problems), and the greater the difference between the wide and long end of a lens, the more compromises are made.

Virtually all digital cameras are going to have it in some conditions, and some cameras cope better than others.

You'll see this comment in this model's review conclusion here:

Chromatic aberrations (purple fringing around highlights) are present, but were well controlled.


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