Yesterday I was working on cleaning and repairing a Balda Super Baldax. Aside from a bit of rust, it's now in great shape with a super bright viewfinder, accurate rangefinder and usable, if stiff, focus knob.
The only problem left is these spots on the rear facing of the rear element. Lens cleaner did nothing, even window cleaner did nothing. They're on the surface, as misting the glass with my breath shows. They don't appear to be bubbles as they are smooth to the lens surface. My guess is the coating's damaged but they really look like the glass has been sprayed with something and left little droplet marks. It's only on the rear element, the rest of the glass is clean.
Any ideas on a diagnosis or what to try? Cheers