Quote Originally Posted by E. von Hoegh View Post
Carbon arcs are typically 35v - 90v, and use high current not high voltage. The vacuum would be a few mm of Hg, not as high as a radio tube. The vapor deposits on pretty much anything cooler than it, you have to shield what you don't want coated. Electron beams have been used to heat the coating materials, remember Fuji EBC coatings?

The trouble is that anything in a vapor phase will deposit on anything cooler than it, so I don't think a carbon arc would produce a clean enough MgFl vapor to result in a useful coating. It would sure supply the heat though.
Look into the work done by Katherine Blodgett for Generous Electric.
I am seeing nothing of value on the net to help me figure out any kind of feasible DIY coating. Certainly there must be a way. Seems to me simply getting a layer to deposit would be half the battle. Seems like there would have to be a way to "set" the coating afterwards, lest it would wipe right off. Probably need more time than a few google searches. Haven't even investigated acquiring some raw MgF2 material. Not interested in "multi-coating". An old Rollei lens springs to mind. As far as the OP's question, I believe this thread has already provided the answers with respect to retaining lens curvature.