OAGs and suitable guide cameras

[halli]

I am now using the GPCAM guiding my 130pds with a ST80 tonight imaging M31.

The quality of the available guide stars wrt SNR has increased considerably compared with the colour ZWO. SNRs of around 6 to 10 times more are now presented ! This has made a considerable difference to the guiding performance with RA RMS error being 0.2 and DEC now 0.1 using PHD2. They were running at around 0.5 and 0.35 previously. This is very encouraging and I think my money has been well spent already ! It has really emphasised how much guding performance is dependant on the quality of he guide star. I feel confident that this sort of performance will allow my RC8 to be guided by the ST 80.

I am now looking forward to using my oag with the GPCAM. I guess I will set it up and get it in focus in daylight this weekend and try it out with the RC8 in anger at the next clear night.

[halli]

Hi All

Just as an update re the use of the GPCAM mono with an OAG.  I have now managed to successfully use this with the OAG on my RC8.  However I need to rotate the OAG to pick up suitable guide stars. With the RC8 this is easily achieved smoothly as it has a rotatable focuser.  However it does add to the set up time.   PHD2 seems to give an almost white screen until a guide star enters the field of view then it darkens to give the normal star with black background appearance.  

Guiding performance is greatly improved with a high SNR star and I can achieve quite low RMS errors  Managed 1500s subs easily the other night  With the ST80 and colour ZWO this was quite difficult to achieve which I have now realised was due to the low SNR of the guide stars which were generally around 10 at best.  

So far so good but I have chosen targets in star rich areas so I need to see what the performance is re guide star availability for targets in less advantageous surrounds !

One of the fiddly issues involved with rotating the focuser is that you are likely to move the scope slightly and decentralise the image after centering it with Astro Tortilla.  If you recenter after guide star selection you may lose the guide star ! Not sure what the answer to this is yet but it certainly makes framing more difficult.  Also because the main camera orientation changes as a result of the rotation, it means that it is more difficult to add more subs to the target later, I guess a means of recording the orientation for a particular target needs to be used so that it can be returned to the same point next time.

Anyhow generally the GPCAM mono seems a realistic cheap guide camera which resulted in high SNR stars and a great improvement in guiding performance and appears so far to be suitable for oag guiding.

Hope my experiences will help anyone else considering a similar approach and looking at a cheap alternative to the Lodestar.

Cheers

Ian