I recently bought an old Pentacon 200mm from ebay and the front element of the lens has the plague! Is there any benefit to fitting a modern multi-coated filter (UV maybe?) in front of it to help with contrast/flare? It had no front cap for years, the original coating's mostly worn off the centre 50% of the lens and towards the edges still has some, with random gaps. No scratches that I can see so at a guess someone 'cleaned' it. Also no fungus that I can see, just the damaged coating. You can't see any odd pattern in shot, but it looks like it's affecting overall image quality with bright areas in frame.