Hello, i'm a little late on this, but you can find some info about 6X7 projectors at: http://people.smu.edu/rmonagha/bronslideproj.html and http://www.a1.nl/phomepag/markerink/proj_667.htm
I bought an used "Liesegang Diafant 6x7" on ebay two weeks ago (370 Euro) and i'm very satisfied with it, the projected image is far superior to 24mmx36mm, my screen is 2m x 2m. Info about it can be found at: http://www.a1.nl/phomepag/markerink/linhproj.htm The sharpness of the lens (2,8/150) is good, it resolves the grain at the blue sky right to the edges (Provia 100F). BTW has somebody experience with 6x7 glassless mounts (8,5x8,5 cm)? I don't like glass-mounts because of the risk of fungal growth and other moisture related problems, but i don't know, if it is possible to achieve a acceptable sharp picture across the whole frame with glassless mounts. Martin Albrecht
