OK, I've found the cunningly concealed rear filter holder on my 45mm, it's a flimsy spring ring around the rear element. I suppose the 35mm fisheye holder will be similar. The infrared filter I wish to use is 0.4mm thick 87C polyester sheet, this seems to be too thick for the spring holder, making the end stick up. I could take the holder off and shim it to the correct clearance, but I'm worried about the mirror clearance. I'm sure I've read somewhere of a problem of an overstretched filter ring snagging the mirror. I use 67II's, but I would imagine mirror clearance is similar in all 67's. The mirror seems to be locked in down position with the lens off (I did not try much force though :-0 ), so I couldn't check the swing clearance directly. Has anyone successfully modified the rear fisheye holder to take thicker filters? Or, does anyone know how much rear clearance I have to play with? It strikes me that a trial and error approach could end up being costly!

-- Keith Davison (keith.davison@ncl.ac.uk), May 14, 2002