[pvelez (Pete)]

Maybe its me...

when getting my gear ready for the move to Coona I decided to ditch the guidescope and use the internal guide chip with the STX16803. I also invested in an Optec 3 inch rotator - a great piece of equipment.

I have also been trying to use CCD Navigator to set up my imaging runs.

The problem I keep rubbing up against is getting a good guide star. The internal chip in the STX is sensitive but small. Unless I have a guidestar well centred, Maxim won't pick it up. The margin for error is very small.

It struck me as odd that when setting up an image with CCDNav and TSX, the bright guidestar I set on the centre of the guide chip FOV in TSX never seems to land on the guidechip. There is always some rotation or - more commonly - a need to shift the mount slightly to get a good guidestar.

The rotator is well calibrated - I check it with regular plate solves.

I'm also on target - I use CCDAP which plate solves each target and does a precision slew to within 15 arcseconds of the target before starting imaging.

My suspicion is that the FOV indicator in TSX doesn't match the actual configuration of the imaging train. It is as if the positioning of the guide chip in the FOV is too far out from the centre of the imaging chip - so when I line up an image using the FOV indicator, the image is correctly positioned but the guide chip FOV indicator sits just outside the target guide star.

Has anyone else encountered this?

I have set up the FOV indicator using the standard equipment lists supplied by TSX.

If anyone has a way of checking this, I'd love to hear about it.

Pete