Quote Originally Posted by Nicholas Lindan View Post
I found the best grease to be 'vacuum grease' - made for laboratory glassware fittings. It won't outgas (read fog the inside lens surfaces), migrate (read gooey diaphragm) or separate into oil and sludge (read seized focusing helical and an oily diaphragm). My experience with silicon (Silglide), Lithium (Lithease) and Calcium (Lubriplate) greases is that they do all three given a little bit of time.

You can also use 'optical damping grease' but it seems to outgas a wee bit and fog lenses when the grease is new. It is probably a good idea to bake the grease first to get the last of any solvents out of it.
There's a grease called "Krytox" that is designed to not outgass. In my Nikkor lenses, the grease is nowhere near the diaphragm, unless you apply it with a grease gun. Other 35mm lenses may or may not be arranged similarly. I've had no trouble with the lithium grease hazing the glass, but I've only been using it on helicoids for about 13-14 years. The brand I have isn't Lithease, it's an instrument type grease. Again, in my lenses, the helicoid is far enough from the glass that it may not be a problem. I think perhaps the most important thing is, not to apply too much. Some lenses I've had apart are greased up like a wheel bearing.