This is a simple modification of a Canon remote to be able to add an extension cord without paying the rather steep prices Canon wants for their extension. ($72 from B&H Photo for the ET-1000N3 33 foot cable)

In any case, don't think about trying this if you don't have at least basic soldering skills, or you're afraid to cut the cable of an expensive remote. (The TC-80N3 runs $130 from B&H Photo.)

Parts


Not much is really needed...just one each:
1/8" mini stereo jack
1/8" mini stereo plug
1/8" stereo extension cable.

I got all three from Radio Shack for about $20.

Instructions

Start with the hardest step--cutting the remote's cord in two.
Then you'll need to strip back about 5/8" of insulation on both pieces of cord. My Canon remote has two wires surrounded by cotton insulation with bare strands of wire on the outside. This bare wire is the ground wire, and needs to be pulled to one side and twisted together.
The ground will be soldered to the ground of the plug/jack (as appropriate) and the two leads will be soldered to the two lugs on the plug or jack. Be very careful to make sure that these two wires match on both the plug and the jack. It helps to connect the plug and the jack, and use a multimeter to check which lug on the plug corresponds to which lug on the jack.
Also, don't forget to put the screw-on shields/outer casings on before you start soldering. Once those wires are soldered in place, it's too late to go back and add the casings.
I should have taken pictures while I was working, but you can see the connections here.
This is the remote without the extension added.
This is the remote with the extension.
And this is the remote in use.
All images on this site are copyright Paul Archer.