Autoguiding with PHD and SSAG, setting advice anyone?

[JacksCreekHack]

Hello,

I have been using PHD to autoguide a CGEM with a C8 using the SSAG on a ST80. Does anyone use this or a similar setup with success? The scope seems to track indefinitely (2 hours is the longest I've let it run). However, my graph looks terrible with RMS in the range of 0.3-0.9 in both RA and DEC. I use 2 star align and 3-4 calib stars with the precision polar alignment feature. I suppose the RMS to be the reason my longer exposures (>5m) tend to give slightly elongated stars? Or maybe it's an optical issue? My goal is for 10min subs on the best of nights.

Any thoughts?

Thanks for your help,

Jason

[robbieince]

Not sure about your settings but if you are imaging without a focal reducer, you are asking a lot of your mount. Rms of 0.5 on the ed80 may be a few pixels on the c8......

Make sure your polar alignment is spot on by drift aligning via the imaging scope before you investigate other errors such as flexure between the main and guide scope.

Regards

Rob

[JacksCreekHack]

I forgot to mention that I use a 2x barlow on the ST80 to increase the FL - this makes it a little more than half the FL of the C8. I am imaging without a focal reducer. I do need to learn to drift align on this mount...

Thanks!

Jason

[Earl]

With SCT's its more common to guide using an OAG

[JacksCreekHack]

I've been seriously considering an OAG. Any suggestions for a good one?

Thanks!

Jason

[robbieince]

I use the sx oag as I already had their USB filterwheel and it interfaces nicely. You will want to keep back focus down to a minimum so I would say either this one or the ts 9mm oag.

Regards

Rob

[Davey-T]

Hi Jason,

I use PHD and SSAG to guide my 10" LX200 and tried OAG but it can be a right pain trying to find a bright enough guide star and getting it all to focus.

I dont think the SSAG is sensitive enough for this .

My scope is permanantly mounted and as well polar aligned as I can manage.

I now use 6.3 focal reducer ,this is far easier to maintain good guiding (10min subs) with and get on with imaging rather than faffing about wasting clear skies on trying to achieve

something elusive ,unless your some sort of masochist

Davey-T