Just saw your second comment on your post Vaughan. The use of the aperture on the lens would not work, since it would not be a cumulative effect for the overall exposure of the exposed parts...i.e. you would ned to make sure each strip is exposed while protecting the rest of the paper. It would also need you to recalculate the exposure times, since generally you print at a selected aperture...at least that is waht I think...Will go off and see if I am correct now! Rgds, K