There are various ways to isolate the Arduino from the device you are triggering. I find Terry King's explanation of relays, etc to be useful (I found his wikis from his store links): http://arduino-info.wikispaces.com/ArduinoPower.
For lower powered DC devices, you can use an opto-isolator (pc817, 4n25, 4n26). Here is Terry's explanation of opto-isolators: http://arduino-info.wikispaces.com/Popular-ICs. The same link also describes the 555 circuits, which is a way to add a delay without an Arduino.
My telegraph shutter release is probably similar to what you want: http://arduino.cc/forum/index.php/topic,117629.0.html.