Hi,
while taking photos of a couple of lenses I'm planing to sell, I noticed a few dots that seem to be on the backside of the front element of my Pentax F 70-210/4-5.6.
They are only visible from certain angles and I've never noticed them before. They haven't bothered me yet but now that I'm selling it I need to know what to tell prospective buyers.
I unscrewed the front lens group, the dots seem to be somewhere between the first three elements but those are screwed together very tightly.
Can anyone tell me what this stuff is?
regards
Jan