Quote Originally Posted by StoneNYC View Post
Wait I'm confused what other tools? The only tools available to me are my reciprocity timer, which asks me about the Bellas distance, however if the bells distance includes this extra space that is outside of the lens area, how can I tell where on the lens this point is? I don't see any special marking telling me where that point is like you do on a 35mm camera which has that zero with a line through it showing that that is where the film plane is, so how can I know?
By "other tools" I mean those tricks one can use with either a ruler or other standard item that you include in the scene, and then read the exposure adjustment off of the image on the ground glass.

Or you could use that fancy math you are trying to avoid