The Bronica uses a mechanical linkage to open the shutter, and uses the electronic timing circult to close the shutter.
The pins in the body move to cause the lens shutter to open, and then to cock the lens shutter.
The design of the Bronica mount supposedly should prevent you from mounting any lens unless both
- the shutter is cocked on the camera, and
- the mechanical levers of the lens are in their proper (cocked) position.
The lens release button also does not depress unless the camera is cocked and the reflex mirror is down (forming a light shield to the film!). In theory,
it should be impossible to unmount a lens unless the body is cocked (which also cocks the lens).
There are TWO mechanical pins (levers) on the Bronica body, one (looking at the body from the front) at 9:30 and the second at 3:30.
The lens has a pair of pins which (after you mount the lens on the body and rotate the lens counterclockwise until locked) are positioned at 9:35 and 3:35.
When you fire the shutter the body pin at 9:30 moves to 8:30 and the second pin moves from 2:30 to 3:30, and the lens' first pin moves from 9:35 to 8:35, and the second lens pin moves from 2:35 to 3:35.
You CANNOT press the lens release unless the body (and lens) is cocked!
If you dry-fired the body without lens attached, its pins are at 8:30 and 3:30, and if you attempt to mount a cocked lens on the body,
the design prevents the lens from being rotated at all on the mount...and therefore the lens CANNOT be locked onto an uncocked body!
To try to unmount the lens, I would first make sure that...
- the multi-exposure lever is in multi-exposure position (particularly if you do not have film loaded so it actuates the interlock in the film back which presses the corresponding pin in the body so that it knows the film has been advanced), and
- then wind the shutter fully (this may entail TWO winds of the Speedgrip to fully cock the body and lens), and
- then try to press the lens release button and rotate the lens CLOCKWISE to unmount it.
