Thanks Ash and Roger. Must confess I haven't spent a lot of time pondering this - thought I go straight to plundering the mass of experience out there
I can't have looked too hard at the EOS PC Liveview program, because I've managed to miss the focus options previously. I'll certainly give that a go. Didn't want to get too deep into software unless necessary.
Roger, I run the scope using EQMOD now, so the PC is always out anyway - just works easier if I'm doing astrophotography at prime focus, which is what's usually happening the majority of nights I'm out. Liveview on the camera or PC works really well for prime focus through the Newt - bright stars give nice diffraction spikes, but I figured I wouldn't have this bonus for widefield through a lens.