In the pinned topic above, Brain says to use alcohol to clean fresnels, later someone else says it can ruin the lens.

My lenses are quite dirty from sawdust, being sweated on and other nasty things. I'd like to replace them but if I order them today I won't get them by Saturday when I'm having my Texas-Ohio State party, featuring my 12 foot PJ. So, anybody know the latest advice on how to clean them?

Try BEVO. He will probably be able to lick them clean.

Seriously, I believe SamuraiJack said to use 409. You might PM him or check his PLOG.

I wonder if would be possible to use a vacuum cleaner for this purpose?

A vacuum cleaner will get loose dust off, but not fingerprints. Personally I think you'd be better off with canned air for the dust anyway.

I'd read in the "care" section for the acryllic that I use in car audio installs that alcohol will degrade acryllic, which is what the fresnels are made of. A quick wipe probably will do no visible harm, but repeated use will almost certainly cause the lens to haze, as will prolonged exposure.

In any case, I think you want something that will remove the oils from fingerprints and rinse away clean. I used dish soap, with a distilled water rinse. (I removed the lenses from my projector, and replaced them with new ones. Then recycled the old lenses for my duct tape piece.) The dish soap worked well, better than what I'd used the first time I needed to clean the lenses.