Last night was quite clear but had intermittant cloud patches. So I set the system to collect thirty images at 400ISO at 4 min and f/5. This was all done unguided so when cloud interfered the autoguiding would not run away chasing a star that was just noise. I managed to get 11 usable out of these images before the cloud really came in.
Details
Canon 5DH, Canon 300mm F2.8L at f/5. Hutech LPR filter.
11X4min at 400 ISO unguided.
full res image 6MB
http://d1355990.i49.quadrahosting.co...03/lagtrif.jpg
As you can see f/5 using the aperture in front of the lens is the way to go to get perfect stars from corner to corner.
Bert