For the purposes of lens testing, I need to photograph a flat target so that the film plane and the target are strictly parallel. I have found that for critical MTF measurements, even small deviations affect the results.
So far, what I am thinking of doing is materializing the normal (line perpendicular) from the center of the target with two Ts, and then attach a laser pointer to one of them. Then I will know that if the laser beam strikes the lens in the center and I point the camera in such a way that the center of the target is in the center of the image, the two planes will be exactly aligned.
I am aware that there are specialized tools such as the zig-align, but I'd prefer not too spend too much money on that project. One should not assume ground-glass focussing and movements, since I might use the procedures with a variety of cameras. Any other suggestions ?