@ Sjizzle
I think I would move the discussion about periscope masks to a proper thread. This is what I got to so far:
...and this is the image you had posted in the other thread:
Before I start packing the file, what do you think? Do they come close to your idea of a dirty periscope, and if your answer is yes, which one do you prefer? The two version use the same dirt mask. I just changed brightness/contrast. Contrast on the left lens looks better in my opinion, but if you like dirt to be darker I can try achieveng an effect itermediate among the left and right scope.
