Bill Cornett , Mar 23, 2004; 09:31 p.m.
George-- Pentax markets a brand of cleaning fluid for their lenses, or at least they used to several years ago. I still have a bottle in my cabinet. However, any optical cleaning fluid made for coated camera lenses should have no abnormally bad effect on SMC coatings.
I know that this is sacreligeous to say, but the coatings on Pentax lenses nowadays aren't much different from the ones on most other camera lenses. In fact, they are probably licensing the same processes that Pentax is.
Just make sure that you apply the fluid on the cleaning paper and then apply the paper to the lens. Don't put drops of fluid directly on the lens itself. The fluid is part solvent, and if it seeps down into the edges of the lens it could loosen the adhesive used to keep the front retaining ring from coming off, as well as make a hash of the guts of modern electronically capable lenses. -Bill C.