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DPChallenge Forums >> Individual Photograph Discussion >> Is this 'purple' from the lens?
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Showing posts 1 - 5 of 5, (reverse)
AuthorThread
 04/11/2007 08:14:12 AM · #1

I used:
Nikon D50
2007/04/10 08:07:58
Compressed RAW (12-bit)
Image Size: Large (3008 x 2000)
Lens: 70-300mm F/4-5.6 G
Focal Length: 300mm
Exposure Mode: Programmed Auto
Metering Mode: Multi-Pattern
1/125 sec - F/5.6
Exposure Comp.: 0 EV
Sensitivity: ISO 200
Optimize Image: Normal
White Balance: Auto
AF Mode: AF-A
Flash Sync Mode: Not Attached
Color Mode: Mode IIIa (sRGB)
Tone Comp.: Auto
Hue Adjustment: 0°
Saturation: Normal
Sharpening: Auto
Image Comment:
Long Exposure NR: Off

This is the data from the RAW file....the posted pic was opened in Elements and sharpened then cropped. No other corrections were made...is there something wrong with the camera or is it the lens?

Thanks
 04/11/2007 08:21:46 AM · #2
It's called Chromatic Aberration (C/A) or Purple Fringing. There are a few possible causes for purple fringing, but most likely it's C/A from the lens in the contrasty backlit areas.

Edit: Your lens is not broken so don't worry. C/A varies with different lenses, but the higher end lenses tend to take care of the problem better. Just watch the background highlights (especially on overcast days) if you have dark objects in the foreground, and recompose if needed.

Message edited by author 2007-04-11 08:31:32.
 04/11/2007 08:21:52 AM · #3
I would think that is is from the lens, I would test it using another lens on a white wall to see if it is the sensor or the lens.

Good Luck
Rich
 04/11/2007 08:36:11 AM · #4
and to "minimise" CA generally an aperture of about f/8 is good. But even that changes from lens to lens. f/8 is a general "sweet spot" for most lenses for sharpness, contrast and CA reduction.

Now i open the floor to someone else who might have a difference of opinion ;-P
 04/11/2007 08:39:31 AM · #5
ok - that is weird, i just looked at the photo. I assume you know what CA is now having read your title again "purple"... i have really no idea what that is, and i doubt it is purple fringing, because, as the name suggests it is on the fringe of something.

One explanation could be the raw conversion technique you used, did you increase the exposure/add "fill light" from an under-exposed photo, because the dark patches could have been a dark purple, you just highlighted it in the conversion.

If you save a jpeg as well, take a look at it - is it the same?
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