[JohnH]

SO I could do another test last night.

It has been suggested to me the steps I am seeing in the error logs could be due to poor centroid calculations in the software. To test for this I set up my mount (it is a Vixen Sphinx btw Rich) with the power off except for the camera.

I just logged the star position as it drifted over the CCD using the PHD software. The results are attached. As far as I can see from these plots there is NO sub pixel position data calculated.

Also it seems that the speed of the camera is an issue - I had exposures set to 0.2s (to collect as much data as possible) but the camera returned only 1 exposure every half sec approx, I assume this is due to the limits of USB2 and a full colour 16 bit image (752x582).

The big spikes correspond to moments when the software reported NO STAR, the on screen image seemed excessivly noisy for those few frames, the wild spikes at the end of the run are where the star left the guide box and when it does that the log shows 0 as the position.

My conclusion from this is rather depressing - this camera/software combination is not suitable for the task I have set it - sub pixel guiding. Unfortunately the OSS is not widely supported in other software and is no longer in manufacture so this is unlikely to improve.

I would love to be wrong of course but I cannot see any other explanation for the steps seen in the trace.

I have tried defocusing and altering the gain/exposure etc to change the behaviour but to no avail.

Next test - revert to the LPI as a guidecam and repeat the experiment, clear skies all.