I am looking for an inexpensive solution for occasional 600 mm shots on 4x5. Alt hough I have a Fujinon T600, the lens is 1Kg and will never leave my car's boot. I have now the bellows for 600 mm and I thought I might try to separate a G-Cla ron 305. The images produced by both the front and back elements look pretty goo d on the GG, focussed right into the corners and with no distortion. The front e lement produces a 450 mm and the back a 610 mm. It should be a light long lens a nd I think I will make some film tests for real performances.

What are your experiences in this field? Can any symmetrical 6 elements lens be used that way? What about an Apo-Symmar? Would the initial aperture of 22 be the best to use as for the whole lens?

Is there a formula that helps determining the new initial aperture of a converte d lens? (f9/300=f16/600?)