Maybe this Tech info & How To document about Rollei Black Magic has some answers for you?
"Have fun and catch that light beam!"
Bert from Holland
my blog: http://thetoadmen.blogspot.nl
my Linkedin pinhole group: http://tinyurl.com/pinholegroup
"I enjoy vintage cameras as “users,” rather than imprisoning them in some display case"
My favorite cameras: Mamiya C330f, Nikon S2, Hasselblad SWC, Fuji GSW690 II, Leica SL, Leica M7, Russian FKD 18x24, Bronica SQ-B and RF645, Rolleiflex T, Nikon F4s, Olympus Pen FT, Agfa Clack and my pinhole cameras.