I need to use a Hasselblad 40mm for a specific photo. I will be renting it, since I don't own one. I also need to use a 10 stop neutral density filter on the shot I'm planning. I cannot find these filters for the front of the lens (either in 86, 93, or even 105mm sizes). BUT I was wondering why can't I use a 40 or 50mm ND behind the lens? We used to use Kodak written filters behind the lens when we shot 4x5 color film (way back when!), but I just didn't know if I was missing anything by using it on a Hasselblad. I'm pretty sure there's plenty of space behind the lens before the film plane (I'm shooting film BTW). My plan was to compose, focus, then carefully remove lens, not touching focus at all, tape ND filter in place, and gently put back on camera. Any thoughts? Thanks!