So after Mike’s revelation that it might be the lens I just had to go back and check my combed photos. Being a geek - and lazy - I decided that it is too much work to do it by hand so I downloaded ExifTool by Phil Harvey (http://www.sno.phy.queensu.ca/~phil/exiftool/)
. What can I say… it is the mother of all EXIF utilities; the BFG of meta-data extraction; the Pan Galactic Gargle Blaster of EXIF tools;
One Tool to rule them all, One Tool to find them,
One Tool to bring them all and in the darkness bind them
Did I mention I was impressed? :-) This thing will suck the last bit of metadata out of whatever image file you throw at it!
To make a long story short - after installing Perl; figuring out which of the endless ExifTool options will dump the data (from 775 raw files 215 of wich combed) the way I wanted it; some more batch files and some tinkering in Excel I can say this:
The combing is caused either by the lens, or a combination of the lens and a small aperture. ISO speed, shutter and exposure compensation do not matter it seems. My EF50mm f/1.8 and EF100mm f/2 USM "comb" quite often. My other lenses never do.
I have updated the web page with the full statistics and detailed conclusions as well as some of Mike’s combed 5D photos with the EF50mm f/1.4 USM. Look at the bottom.