When calculating aperture widths using the formula Focal Length/F Stop, should the focal length actually be the flange plate to focal plane distance?
The reason I ask is that I'm doing a Nimslo panoramic conversion, using a Bronica 40mm lens, and the flange plate to focal plane distance is 76.5mm. I used 40mm in the aperture width calculation and have ended up with a roll of underexposed film.
It would seem that I should use 76.5mm as the focal length (possibly?), but I've not been able to find any information about this.
Anybody had any experience of this?
What John said. Also, if that would be true all your lenses would have the same focal length. The focal length is the distance from the rear nodal point to the focal plane at the lens' infinity setting. Finding the rear nodal point is complex and depends on lens design.