Shpaget:
I am not familiar with LA-2A Compressor, but an optocoupler is basically a (photo)transistor that (in this case) acts as a switch depending on the state of the LED on the other side. The important part is that the two sides are galvanically isolated from each other meaning the current from one side can not enter the other side (as long as you keep within specs) effectively separating your circuit into two.My Canon DSLR will also focus if shutter pin is grounded (regardless of focus pin) if the lens is in AF, so you might want to put it in MF after all.
Thanks for the explanation.
My understanding is that when in MF, grounding the focus pin will still focus right?
My idea was set camera to MF, set up the scene, trigger focus simultaneously, and then trigger shutter releases simultaneously at regular intervals.