Thats not possible on the lens the picture is from (maybe on the other one and since its inside). The focusing helix is too far from the element shown (maybe 5") and the apature is inbetween. this stuff isn,t anywhere else on the lens (that I have seen). I don't know for certain that it the same either as I'm looking through the glass th see it on the other one.
these pictures are from the rear element from a Tou / Five Star 1:8 f = 500mm Telephoto Lens. Yea I know its a piece of junk but it was 20$ shipped and after a cleaning its in very nice nearly unused looking condition.
the other lens is an old full manual sears auto mc 50mm 1.7. If I can find a screw driver (I only have 1 that fits lens screws well) maybe I'll open it up now.
Originally posted by rhodopsin Could be oil droplets from overheated helical grease. I'd try removing with a few drops of lighter fluid (contains naptha, a solvent) on a pec pad or lens tissue, then remove lighter fluid streaks using lens cleaning fluid such as Eclipse or RoR.
Please, tell us which lens is it?