PA with autoguiding

[chemtom24]

Will I still need to polar align when my autoguiding gear arrives? If, so, can it just be rough or does it have to be bang on? surely if the scope is autoguiding then it shouldnt matter??

[SteveL]

Autoguiding wont eliminate field rotation for longer expsoures if your PA is out by a lot, so its best to get it as accurate as you can.

[James]

I used to be fairly casual with PA when autoguiding but after spending 30-45 minutes one night drift aligning found that my tracking improved markedly - it's worth getting PA pretty close.

James

[chemtom24]

thanks

gotta ask tho, if i still need to drift align, then why the need to use autoguiding? I thought autoguiding did it all for you? ie, found 2 stars near the object you want to image, and kept thenm in a constant position, thereby eliniaintg star trails etc?

[James]

Autoguiding helps to counter annoyances such as periodic error amongst other things

[Ben Ritchie]

Autoguiding reduces the effects of periodic error in the mount's RA drive, even if perfectly polar aligned stars will still elongate from PE unless the mount's tracking error is below the image scale.

[chemtom24]

ok thanks all i was hoping to dodge a bullet lol

[SteveL]

Once you make it all part of your setup routine, you`ll be amazed how little time it actually takes.

[SteveL]

oh, and autoguiding also reduces the effects of your PA moving during a session when you set up on a grass surface that is still a little "soggy" and the weight of the tripod and kit is making it all sink very very slowly on one side....

[brantuk]

There will allways be error with polar alignment on amateur telescopes. Impossible to get it 100%. However, the closer you can get it - the lesser the tracking error will be. So the corrections fed back to the mount will be correspondingly smaller and guiding will be that much more accurate.

I understand drift alignment will eliminate error even more but never tried it myself

[FraserClarke]

There will allways be error with polar alignment on amateur telescopes. Impossible to get it 100%.

That's true for all telescopes, not just amateur ones.

The 3.9m AAT in Australia has a wonderful plot of the polar axis shifting by ~30 arcseconds over ~20 years, probably as the concrete in the telescope pier slowly cures!!

[ollypenrice]

What you find with poor PA is that long subs will show rotation and so will your stack even if, within each sub, no visible error is generated. Better stacking software corrects for rotation but some doesn't, only aligning in x and y.

In fact perfect PA may not give you the best autoguiding. Some people go for a deliberate offset so that guiding corrections always go one way. This means the mount is not being prodded by the guider into oscillating across its own Dec backlash. It is the Dec equivalent of running slightly heavy on the east side so as to let the mesh fall onto the same side of the gear.

Olly