Arduino based Stereo Canon DSLR Interval Trigger

[sbright33]

Why?  What is the purpose?  What mistake could you make that would damage the camera using my simple circuit?
I'm asking because I don't want to make that mistake.  I have been using my circuit for 1000's of pictures and 2 years.

[NNC1]

Why?  What is the purpose?  What mistake could you make that would damage the camera using my simple circuit?
I'm asking because I don't want to make that mistake.  I have been using my circuit for 1000's of pictures and 2 years.

The sources I have looked at seem to suggest its a good idea to isolate the camera from the rest of the project.

Can anyone explain why you need isolation or why not?

[sbright33]

Static electricity?  Mistakes in wiring?  If the supply voltage was too high? 
It's a high impedance input, you cannot get much current to flow even without a resistor.