I've got a RZ67 Pro II on the way. I guess I should have specified the model. The mechanical cable release I was referring to is the one on the lens.
For mirror lockup, using a mechanical cable on the lens, these are the steps, according to the manual:
1. After screwing a cable release firmly into the Mirror Lock-up Socket of the lens, the socket will elevate slightly and the camera will be ready for mirror lock-up operation.
2. Press the Cocking Lever as far as it will go. Step 2 may either follow or precede step 1.
3. Depress the Shutter Release Button and the mirror will rise, but the shutter will remain closed.
4. Press the plunger of the cable release and the shutter will operate.
Is there any advantage to purchasing the more expensive electronic cable? Are the steps outlined for the mechanical cable on the lens, basically the same for the electronic cable attached to the body?