Do you already have the 35mm adapter? If not, you might want to consider the M2 from redrockmicro.com. It comes with two GGs, one of which is grainless. It uses a coating to achieve its opacity instead of etching. Virtually no light loss. The other GG is more traditional. With a vibrating system (the M2 is rotating) I can only guess, but would wager you'd see more grain if the oscillations aren't fast enough. Again, just a guess. Just what you wanted, no?