I have found that household ammonia cleans quite a bit of fungus off the lens. That and keeping the glass in bright sunshine for extended periods of time both help to attenuate that scourge. As far as the scratches go, BIG scratches best be filled with opaque material as michaelbsc has suggested (#3). - David Lyga
I have recently acquired a Sonnar 150mm for Hasselblad, which looks like it was dunked in the ocean, so perfect for doing some real-world testing. Lots of cleaning marks on the front element, and toothpaste didn't do anything to the ruined coating. I then tried aluminum polish which cleaned it up. I haven't done testing yet but it looks markedly better and much more reflective than it once was.
Possible? I don't know. If it requires recoating I think you'd be better off avoiding situations that produce flare and get a good lens shade. OTOH, if it residual cleaning material and it needs some sort of disassembly, recleaning and polishing, you could try these guys at Midwest Camera. They give online estimates that are pretty reasonable.
Also, since you're in NYC, NY Lens and Repro merged with Calumet. NYLR always did great repair work and since they're in with Calumet now, take a ride down there and ask them to take a look. Calumet Photographic at 22 W 22 Street, NYC. It might be worth having them check it out.
I went at a front element the other day with toothpaste (the plain white type ) together with hydrogen peroxide and methanol to prevent it from drying out. Went at it for half an hour and it didn't do squat. I'll have to try some other polish.
I bought some Cerium Oxide last year when i bought new stocks of polishing grits. I had to make some Rollei focus screens for a Microcord & Rolleicord III and decided to give the Cerium Oxide a try after the #600 grit I normally use - the reults were the glss began to polish smooth losing the ground grain. The Lapidiary supplier I use had told me they mainly sold Cerium Oxide to telescope makers.
Originally Posted by Gerald C Koch
All you guys using abrasives like cerium are taking the glasses out of the cell and using pitch blocks to polish them, right? Because if you don't, you'll spoil the figure of the surface and have a nice shiny paperweight.
There's a reason it's expensive to get lenses repolished, it takes skill and special tooling made specifically for each job.