Autoguiding and Drift alignment

[Uriabraham (Uri)]

Hi all,

I haven't done AP yet but wanting to start soon. I have learned about drift alignment and autoguiding and I would like to know the following when using a method of guiding (Off-Axis or guidescope);

1. Do I still need to do drift alignment ?
2. Can a finderscope (I have officina stellare 12x60) be used as the guidescope or must I have a separate guidescope for guiding ?

I hope the above makes sense
Any help appreciated

Uri

[graham.hobart (Graham stevens)]

Yes, guiding is much more successful with accurate polar alignment- makes the mount and guiding set up work less hard. IF PA is poor you may not keep guide star in guide box on your guide package.
Finderscopes make good guidescopes as long as you cn bring your guide camera to focus- I use a modified finder with the SSAGuider.
Good luck
Graahm

[Shiraz (Ray)]

Polar alignment should be as tight as possible, or you will get field rotation as you track. A little bit might be just tolerable as stacking software can correct for rotation between subs. Any significant rotation within the period of a sub will cause star trailing. If you have poor polar alignment, the mount will need to regularly correct DEC, which can upset RA tracking on lower cost mounts, as Graham points out.

Don't know about that specific scope, but you need either a guidescope with a tracking camera alongside your main telescope or an off axis guider (OAG) which diverts light from your main scope to the guide camera. I use a modified 60mm finderscope with a QHY5 camera for the guidescope - if your scope takes 1.25 eyepieces, you should be able to do something similar. OAG gets rid of differential flexure, which can be a problem with some scopes and might be the best solution if you are imaging with a Newtonian scope.

[Uriabraham (Uri)]

Thank you Ray and Graham, your replies were

Uri

[LAW (Murphy)]

Originally Posted by Shiraz

OAG might be the best solution if you are imaging with a Newtonian scope.

Thanks everyone, you asked and answered a few questions I'd been meaning to clear up. But the last bit confused me, are newts particularly prone to flexure or rotation? I thought 1 degree was 1 degree and as long as both scopes are rotating around the same axis (and that axis is polar aligned) then it wouldn't matter?

[Shiraz (Ray)]

hi Murphy
Newts are a bit more prone to things moving about - the mirrors are often held in relatively flimsy structures and the tubes can flex and sag - particularly near the focuser - as the attitude varies. If your guide scope is solid and your Newtonian flexes about, you will have odd star shapes, since the guide scope might be pointing where you want it, but the Newtonian may be pointing where it wants to. If you use an OAG, it will not matter. Of course, you can buy Newtonians where everything is bolted down - CF tubes, heavy spiders, multiple strengthening rings etc, but the run of the mill ones are not like that.