i got this problem on my istD that happens with all my lenses. there are about 5-14 (depends on type of picture) dark spots appear. its not the lens because they appear in the exact same position every time. it also seems to show up worse on blue sky than anything else.
i put the worst one as a full size jpg exactly as it came off the card online http://www.xdstech.com/istd/IMGP0522.JPG the shot was taken with the fa 135mm 2.8 1/3000 f13 it was shot with the sun just at the edge of the roof. i count 13 spots (some quite faint and some glaring) any idea what it might be? dirt on the sensor? arnie