What kind of defect is this?

artefacts

Its discolouration is caused by a demosiacing problem, caused by using W/A adapted lenses. The sample is small. Do you have a "maze" type pattern as well?

This is about it the problem. http://www.flickr.com/groups/1084614@N23/discuss/72157622637978730/?search=mazehttp://www.flickr.com/groups/1084614@N23/discuss/72157622637978730/?search=maze

Its because the lenses are film lenses, not designed for digital. Are you processing from a Raw file in Photoshop or Lightroom?
Previous problems have been cured by a new version of Adobe Raw converter. If the problem is from raw, then you could try another converter.
If its on the jpg. its not fixable. Its a lens mismatch

 

This "Maze" effect has got to be a result of some software algorithm in the camera or post-processor running amuck trying to do some sort of anti-aliasing?

This problem does not occur when using "film lenses" on a Leica M8 (or M9), which do not have AA filters. Nor did it occur on my old color Kodak DCS series cameras.

Whatever firmware that has gone wild, is there a way to disable it? I'd rather have the moire effect that creates a couple of speckles in the image than this crazy pattern!

Looking at some sample images: you would get artifacts that look like this with some sharpening algorithms. Would in-camera, or post-processing, sharpening settings affect this artifact? A long time ago, I just learned to turn sharpening off on my Digital cameras.

 

it's great to have Brian S on this forum - adds another very knowledgeable dimension

(I am/are/have been a lurker on the RF forum - so I "recognise" Brian)

 

Try using the Olympus software to process the file. In the case of the problem that I linked to, this was happening on Panasonic cameras processed in Photoshop or Lightroom. It DIDN'T happen if the supplied Silkypix software was used. The Olympus raw conversion software may solve the problem.
Theres no way to fix it in CR 5.6. With the Panasonic problem it only got fixed when a new version of Camera Raw was brought out.
I personally had this problem with a Voigtlander 15mm lens. It now works fine on Panasonic cameras but not on my Olympus E-P2.I get the same problem that you do.
It does only seem to happen on M-mount wide angles, and Voigtlanders are prone to it + some Zeiss lenses. Some lenses seem unaffected by it. A lot of the Zeiss lenses are made by Cosina who also make the Voigtlanders and they were designed as film lenses.
Hopefully the Olympus software will work and Adobe will update their raw converter to eliminate it.

 

It only happens with m-mount lenses on m4/3. The same lenses are fine on the Leicas.
Its seems its a software "omission" that happens when files are processed in Photoshop.
It took a while to track it down and it did get solved for Panasonic files. However it seems the software algorithms that Olympus has passed to Adobe haven't caught up with this "bug" yet.