Guidescope: Where should I point it?

[stillneon]

I have a 30mm F4 guidescope that is attached to my Star Adventurer L bracket. I know ideally I should point near the imaging target but given the limitations of my fixing that's not always possible. For example if I'm imaging in a southerly direction. My question is: does it matter where I point it?

Thanks in advance.

EDIT: I should say, this is for auto guiding purposes.

Edited April 3 by stillneon

[PhilB61]

Lot's of people don't guide exactly on their imaging target, but I think the closer the better. I don't know what the acceptable tolerance would be maybe a couple or 3 degrees? It's not going to work if your imaging scope is pointing south and you guide on a star say in the east or west, as the apparent motion of the stars changes depending on where in the sky you are pointing.

[ollypenrice]

I think the tolerance of guidescope offset is related to the precision of your polar alignment. If you are polar misaligned, the guider will cause the imaging scope to describe a circular path around the guide star during the sidereal day. The position of the guidestar relative to the centre of the image determines the size of this circle - or so it seems to me.

In reality you can point the guide scope considerably off axis. That's what adjustable guide rings are for. They are not there to let you align the guide scope with the main but to search off-axis for a guide star. This used to be necessary when guide cameras were far less sensitive.

Just remember that, if you change the guide scope position, you will need to recalibrate the guiding.

Olly

[stillneon]

Many thanks for the responses. I do try to get a guide star further away from the zenith than the imaging target rather than the other way round. Not sure if that makes a difference but I do remember things getting much more hectic on a playground roundabout as you got further from the axis. My logic would be that guiding on a star that is 'moving' faster than the imaging target would provide the best results. Or maybe, I'm completely wrong....

[michael8554]

If you're using PHD2 to guide, the PHD2 Calibration Assistant will slew the mount to near south and Dec = 0 before Calibration starts.

PHD2 will then automatically adjust the RA guiding to match the higher Dec of the target you eventually GoTo.

So if the guidescope is pointing considerably far off Dec = 0 when the mount is at Dec = 0,  that might affect how well PHD2 guides RA on the target.

Pointing the guidecam at Dec = 0 will still confuse, as PHD2 will still calculate based on the Dec of the mount.

Michael

[malc-c]

I set my finder / guider up so that the same subject is central in the viewpoint.  The main scope was centred on a bright star, then using sharpcap the same star was centred in the finder/guiders view.  The 9x50 scope provides enough field of view for PHD to pick a star and guide without any real issues.  Having the two scopes pointing at the same section of sky makes more logical sense to me.