[JohnH]

OK, so I have got my system almost doing what I want...attached is a crop of a 10 min test run on the Keyhole region. My stars are not round but little triangles (no its not a collimation problem). I use PHD to guide and the corrections were applied on both axes with DEC in one direction only. Exposure was 3 secs and I set the erorr window to .05. The error log shows corrections only being applied in one direction and typically taking 2 small pulses to re-centre the star.

So I think my problem is lack of sensitivity to the errors but I am not sure I can go below .05 (ie guiding to less than on twentieth of a pixel?) so I need to barlow?

My Guide scope is a WO 66ED - 388mm fl with an Orion Starshoot on the back (3.43" per pixel), imaging is the VC200L - 1800mm fl with the 20D on the back (0.74" per pixel).

Using those numbers I thought I would be ok without a barlow???