Firstly, apologies if this question has been answered elsewhere. I've been scanning the forums for days, but can't find exactly what I need.
I am trying to build a remote shutter release for my Nikon D700 and D800. I want to be able to control the shutter via my laptop. This should be the simplest project in the world, but I can't get it to work.
I'm using an optoisolator (4N25), connected as follows:
Pin 1 connects to the D13 pin of the Arduino
Pin 2 connects to a resistor, then to ground
Pins 4 and 5 connect to the ground and auto-focus contacts of the camera.
Initially I just want to make sure that I can auto-focus the camera (equivalent to half-press of the shutter release). When I make the D13 pin go HIGH, the resistance between pins 4 and 5 on the 4N25 drops to about 100 ohms. But that doesn't seem to be low enough to make the camera auto-focus. Many people have built a similar devices, but no one mentions this issue.
I'm sure the electronics side of things is correct. Could this be something specific to the D700/D800?
Any assistance would be much appreciated!