Hi Houghy,
Do you already have the Canon timer that this adapter cable fits?
You can easily make an adapter cable to allow computer contol of Bulb. If fact I have made a few and could do you a deal.
http://www.ecoscentric.com/~paulb/as...rolCables.html
You can use DSLR focus or many other apps to then control the bulb exposure... Much cheaper than getting the canon timer & adapter cable, unless you alredy have the canon timer...
Hope this makes sense!