Hasselblad 40mm; can you use filters BEHIND lens???

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!

No! You need a huge screw-in filter (93 mm?), but a square filter adapter is more practical. Get one with a short compendium lens hoot. There is no provision to attach a filter to the rear of the lens, and doing so would significantly affect the focus and lens correction. There might not be enough clearance for the mirror.

...i don't think you need to be such a purist as suggested. I'd definitely try a taped gelatin filter. Doubt if there'd be a focus shift with something so thin. It may not matter too much if your abberrations are increased - you're not proposing to shoot through a piece of double glazing covered in grime!

The effects of putting a plate (filter) behind the lens is discussed by Kingslake. The focus will change and be pushed rearward a bit but if your depth of focus is deep enough via smaller stops it will not be noticed. The added aberrations will be minimal. I had done what you are suggesting on a Pentax 35mm Fisheye (6x7) many years ago with success.