"CCD Bloom" or Chromatic Lens Aberrations?

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twebster
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"CCD Bloom" or Chromatic Lens Aberrations?

Post by twebster »

Hi y'all :D

There is a lot of confusion on the Internet as to "purple fringing", "green fringing", chromatic aberrations, and "ccd bloom". Actually, the ccd and cmos sensors used in todays digital cameras are very well shielded against "ccd bloom". CCD bloom is a very rare occurance. You have to practically point your camera at the sun with the aperture wide open to cause ccd and cmos bloom. The green and purple color fringing are the results of under-corrected chromatic aberrations in the camera lens design.

I ran a little experiment a while back to convince myself, and others, that the green/purple color fringing was the result of under-corrected chromatic lens aberrations. If the green/purple color fringe is the result of "ccd blooming" then images made with film should not show the color fringing. Well, film images exhibit the same green/purple color fringing, too. I used my microscope a while back to make an image of the color fringing recorded on film. I took a little time off from our packing to write up an article on color fringing and posted it on the photomacrography website...

"CCD Bloom" or Chromatic Lens Aberrations?

Enjoy, my friends :!: :D
Tom Webster
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Phoenix "The Valley of the Sun", Arizona, USA

Think about this...maybe Murphy is an optimist!!!

rjlittlefield
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Post by rjlittlefield »

Tom,

Thanks for the article -- excellent illustrations and discussion.

I find that most of my lenses have some visible chromatic aberration (CA). I used to just live with it, but the tools for removing it digitally have become so good that I have recently started to remove CA from all my images as part of routine processing.

The "camera raw" converter in Photoshop gives excellent results and is easy to use if you shoot that kind of images. In addition, there is a free program named PTLens that works on any kind of image (jpeg, tiff, etc). It runs as either a Photoshop plugin or a command line program and can be used in batch mode to correct large numbers of images that were all shot under the same conditions.

Your readers may also be interested in another article on chromatic aberration that appears in the Panorama Tools wiki. It discusses and illustrates both green/purple and cyan/red CA, as well as several other types of color defects that look like CA but aren't.

--Rik

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