Hi Rich, The rear element of the lens is just about the same diameter as the front element so no matter which side I filter, its gotta be pretty big. The lens is a U.S. Army surplus 254mm made by Elgeet in the 1960s and has a quick release mounting plate. I paid $17 for it on eBay and it came in a custom made, velvet lined, metal case complete with a Tiffen red filter and series 8 lens shade. I was the only bidder. Hah! Admittedly I know very little about lenses but I'd say it was a good deal. Greg > -----Original Message----- > From: CameraTraveler@aol.com [mailto:CameraTraveler@aol.com] > > << So I was wondering if anyone has a slab of neutral density > filter at least > 65mm in diameter >> > > Greg, > Would a smaller filter fit on the rear of the lens? > > Cheers, > > Rich Mason > Photographer-at-Large > <A HREF="http://www.richmason.com/">http://richmason.com</A> > See the new section: Rich on the Road