> When you fill in a scratch with black ANYWHERE on ANY LENS SURFACE > you are in effect "stopping down" a very slight amount, the only > side effect is slower lens speed but still full quality. IF you > leave scratched or filled clear you are creating an improper lens > suface which will bend light rays in the wrong direction(s) which > is far worse than the slight "stopping down" effect of blackening > it out.
Well, yes and no, I think. While an untreated scratch will cause incorrect diffraction (and also may cause an increase in flare), a blacked-out scratch must also cause a small increase in diffraction effects. (Still, I would prefer treating the scratch - I've done this on two user/beater lenses, and I've also done so on the scratched mirror of a Schmidt-Newtonian telescope.) Fred
