Thanks for your input. I have solved the issue a few weeks ago (posted 19 June I think)
I have an Acer 310 and was aware of the Com port, but didn't know the number because there are simulated ports, and that it was not physically exposed except on the connector.
I did exactly as you have described, wiring into the cable 26 minute pins which has a USB on the other end. I just brought out earth and RTS which worked fine. I just thought that USB would avoid any wiring.
I am using this new cable with a program I have written for Time lapse photography, triggering the SLR via wireless, from the Acer. Works very well.
There were two web sites showing the pinout, I believe I posted somewhere on this forum that one of them is totally wrong, possibly a Russian one. Beware anybody doing the same.
My cable of course now has a dangling USB connector. If your connector is 26 pin as on mobile phones I would be grateful to know where you got it to build your cable. I would much rather do as you have from scratch and perhaps put a full serial on the end.
Thanks for your offer of pinouts but I have them for mine.