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thanks guys for the responses.
Greg, the Tpoint manual suggests you shoot for the refracted pole. For my area it is +72 seconds. Since my ME is +70 I left it at that. It could well be that this difference might cause some rotation but why on some images and not on others? Perhaps it is a declination thing. Although the B92/93 images show next to no problems with the stars and it is one of the furthest dec objects I have shot since sorting pointing and guiding.
It could be a little mis registration but on the subs there is some elongation, so perhaps a contributing factor. I am using CCDstack for registration, but I have not used CCDIS. Perhaps I should?
I don't agree about the idea that doing shorter subs is better. Longer subs give you a stronger signal to overwhelm the background noise. Most technical tuts suggest getting a background ADU of 1000. Shooting for 10 minutes only gets my data to 800 with this size scope. I have not seen any significant difference in the star sizes since trying this out. The wells fill but as yet I have not seen oversaturation. The star colours always seem fine, would you not agree? This is shooting at f5.6, perhaps this whole business of shooting shorter is a myth. Someone with the maths can explain here if they like.
I think you are right about the ME. I'll shift that back down and redo a pointing run in the coming weeks.
I am not using the non orthagonality term in my model. It did not seem to make any real difference to the model.
The focus is a good point and that is what I have been doing. Every hour I check focus to ensure that everything is nice and sharp. I have not as yet done a test to see if all the filters are truly parfocal. I will put this on my to do list.
I think PE is ok, but I wanted to check the run again. There was a blip I saw when I did it and wondered what was going on there.
As for cables, I have my cable management well and truly sorted. Nothing stray, all neatly wrapped and going through the mount with a large loop like the manual suggest.
Stuart I will take a gander at that too. A slightly out of focus star image will certainly help decide what is going on.
Once again guys thanks for your suggestions. It is really nothing on the image but I want to sort this out. I am always aiming for perfection.
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