I've bought a very nice Mamiya RZ67 professional with a 90mm c lens. I'm very happy with it but something I don't understand.
Is it possible to make bulb exposures?? when I set the lens on T then the shutter wil open but only closes when I move the lever. This is not very handy because of camera shake I think.
Yep! If you are using a tripod sturdy enough to support the camera without moving easily, turning the shutter speed dial will have no effect. I do this with my RB quite a bit and I've never seen movement problems.
Another option is to put a dark piece of card (cloth, hat, etc.) up to the lens before you close the shutter. Then any shake caused by touching the camera is not recorded on the film.