Chromatic aberration and back focus
 

I had changed the back focus on my camera to fit a minolta zoom lens on it, so that it could zoom without losing focus.

But as I now have a proper C-mount machine-vision prime lens maybe the back focus needs to be redone. Can the chromatic aberrations be caused by having the back focus set incorrectly?

Most certainly yes they can.

From HDTV Lens Design: Management of Chromatic Aberrations, by Larry Thorpe and Gordon Tubbs:

"...it was fully recognized by all of the camera and lens manufacturers that chromatic aberrations were a regrettable impairment that could never be totally eliminated. The camera manufacturers and optical manufacturers worked within the Broadcast Technology Association (BTA) in the late 1980s to address all aspects of the 2/3in HDTV camera and lens interface.... The studies included grappling with the issue of longitudinal and lateral chromatic aberration and its variances with focal length. A key element within this standard was the agreement on a precision Flange Back dimension..."

At http://www.usa.canon.com/industrial_...WhitePaper.pdf

Chris,

I am not entirely convinced by this article, as it is about zoom lenses, not primes. I will play with the backfocus to see if I can reduce the aberrations.

Of course my development version of Boom Recorder is completely trashed right now, so it will take some time before I can do this test.

Cheers,
Take

Sorry, yes, that entire series of white papers involves HDTV zoom lenses.