Plate Solving

[Altocumulus]

I have a finder scope atop my 180 Mak - almost well synced (!)

I know SharpCap has a "good" description for my polar alignment - my NEQ6-R doesn't let me get any better than that - the threads on the bolts not fine enough.


Using finder scope not the Mak!

2 evenings ago, from Home park, I slewed to Jupiter through cDc. I then plate solved and the routine quickly ( first time ) solved, centred and synced. After a short while I started to move off to Saturn, but discovered the mount was going the long way round, so stopped the slew. A re-slew to Jupiter failed to find the planet. I plate solved and synced again. The mount didn't return to Home park at the end of the evening, it was a couple of degrees off NW I corrected manually.

Last evening I didn't 'hit' Jupiter first slew, so had to solve/sync again. I further plate solved on Mars, Neptune and Andromeda as 3 extra points to add to the file - returning to Jupiter I again missed! At the end Home park was correct.

I've checked, the file is being updated and saved.

There's no play in the mount and the tripod is rock solid between concrete blocks beneath my shed.

Is there anything I am missing in why the finder scope isn't getting targets at least in FOV? It's a 50mm F4 with Altair 178mm cam. Is it as simple as needing more alignment points?

Geoff

[admin]

Hi Geoff,

I suppose there are four things required for accurate goto movements

1) Good polar alignment
2) Accurate mount movements
3) Minimal cone error
4) Everything stays solid during a session

It sounds like you have decent polar alignment, so let's skip that.

Hopefully the mount is moving accurately, but you mention alignment points - setting up a pointing model using mutliple alignment points is fine, as long as the alignment points that go in are accurate. If you set it up somehow with bad data then it will throw things off in future. If you can turn this off without losing the data, it would be worth testing without. Certainly the sort of errors you would be expecting to correct with multiple alignment points are far smaller than the ones you seem to have.

Cone error is a possibility - this is if the scope is pointing out away from or in towards the plane of the dovetail holder. It's called cone error because if you have it and you have the mount in the home position and spin it around the RA axis, the axis of the telescope will draw out a cone. A cone error of 1 degree can leave you up to 2 degrees out if you slew to a part of the sky that is far away from where you last synced.

Finally, if you are using a tripod rather than a pier, there is the possibility of things moving after polar alignment, particularly if the ground is soft.

Hope this provides some things for you to consider,

Robin

[Altocumulus]

Thanks Robin.

I doubt the tripod moves, it's well embedded.

I'll look into cone error, though I'm currently using the finder for solving. It's firm in its setting, but worth a look. Might consider going straight to the 180 scope for solving, I note it's not impossible if the star density in view is enough. Would be useful to ditch the weight as I have enough on the bottom end of the scope.