Mamiya 6/7 and RZ67: Why There Are No In-Between Shutter Speeds
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
I’ve been asked why some cameras will not produce an in-between shutter speed on the shutter dial. While mechanically controlled shutters have their own reasons, I’ll speak here of two electronically controlled shutter cameras, the Mamiya 6/7 and the Mamiya RZ67.
On the Mamiya 6/7 the shutter speed is input by a binary code. Photo one shows initial disassembly of the shutter speed control and photo two shows the lowest level of the speed control, the wiper and PCB for input of the four bit Grey Code. This type of code is often used on electromagnetic devices to eliminate ambiguity of signals from a wiper and circuit board. So, output of this switch runs from 0000 to 1111 and this covers AE, B, and all the shutter speeds. Not possible to select an in-between speed. However, Mamiya used resistors to select ISO speeds as you can see in the resistor board in photo three.
The Mamiya RZ67 used a different approach than the Mamiya 6/7 in shutter speed control- photo four shows the shutter speed control board with the various discrete resistors for each shutter speed. So, again, no way to select an intermediate speed but for a different reason.
