Centering defect?

[shadowfax]

Would someone describe what centering defect means?

TIA,
Christopher

[rogprov]

It means that, usually through lax quality control, the individual elements of a lens have not been optimally adjusted. It could also be as a result of damaging the lens or dropping it.

[shadowfax]

Thanks for the information. Just my guess, but I'm thinking it had a centering defect. After reading reviews of Canon's 24-70, it took photozone.de 4 samples to get a good copy. According to them it was a centering defect. That is why I asked.

Received a 24-70Z about a month ago. Only to realize the the autofocus was missing its mark 90% of the time. I checked it against:
-other lenses at the same focal length (e.g. 28-75D, 70-200G)
-used various focusing charts, everything spot on except the Zeiss
-confirmed depth of field and focal plane using a tripod, distance, et. al.
-same problem on second A700

Returned it to Sony for a full refund. Received my new one today, and it seems spot-on, of course minus some poor techniques on my part.

1) Any other suggestions on why the it missed it's mark? I read on some forum, that it's always a problem with the alignment of the three light planes of the camera.
2) Would a centering defect also affect the 24-70Z distance scale?
3) Are there limitations of the 24-70Z on the A700 body?

TIA,
Christopher

[springm]

according to my knowledge a centering defect should show up through different sharpness in various parts of the image. What you describe sounds more like a poor calibration of the autofocus system.

Regards - Markus

[01af]

According to my knowledge a centering defect should show up through different sharpness in various parts of the image.

In fact, de-centering will show up as poor sharpness in the whole frame, low contrast, and strong chromatic aberrations---i. e. poor lens performance generally. With such a lens, focusing is hard because the image never will be really sharp. So centering problems may affect auto-focus performance indeed.

Different sharpness across the frame is a symptom of poor alignment of the various parts of the tubes that make up the lens' barrel, or a mis-aligned bayonet mount of lens or camera, or a mis-aligned sensor. It has nothing to do with de-centered lens elements usually ... however in a broader sense of the word, these problems may be considered 'centering problems,' too.

-- Olaf