By Golly I knew this forum was worthwhile - a big Thank You to Gary Beasley for jogging my little grey cells. The idea of ND filters behind the lens is good - but they would make the GG screen so dark that my old eyes would have trouble seeing to focus. The Beck Symmetrical only opens up to f.6 or so.
But what if I could see at FULL illumination and the film could see many stops darker....each film is enclosed in one side of a double dark slide. Nestled in a slot and locked in by the end cap. Suppose I cut a piece of transparent material into a 4 x5 shape and stacked it on top of the film. Perhaps an evenly-exposed sheet of film developed to a dark filter. Perhaps a dark blue sheet of cellophane to replicate the exposure characteristics of some old films. Perhaps a red sheet for dramatic effects.
Each sheet with its own ND filter. If the filter is dark enough the lenscap could come off for 1-2 seconds. I might even be able to use a head-clamp on the portrait subjects! Any optical aberrations in the cellophane would contribute to the historic look.
Does anyone know if the slot of a standard Lisco double dark would hold 2 sheets of film?