ASGT problems again!

Hi all,

Sorry to bother ye about this but just wanted to know if anyone had seen a similar problem recently (I had an old thread about it but this was some time ago).

I'm thinking about sending the CG5GT mount back for repair again as it is still trailing at very low exposures and focal lengths, even after polar alignment. Before I do that I just wanted to check if someone sees that I am doing something wrong.

What I did last night was:

1/ Polar align the mount using a polarscope (it was collimated)
2/ Three star align with 10mm plossl (up and right on approach)
3/ Polar Alignment utility on handset (this always messes up by turning the scope upside down with the counterweights pointing roughly 45 degrees up towards the south & Polaris a few degrees out of the fov).
4/ Adjust mount to point at Polaris.
5/ Switch off for a minute.
6/ Switch on for another 3 star alignment

Well, after step 6, gotos and tracking were actually worse, in fact the 3rd alignment star is never within 3 degrees of the fov.

To diagnose I ran a series of 100 x 30 second shots and drift is usually in one direction, however, fully 25% of frames were drifting orthogonal to this & about 10-15% were perfect! Sounds very odd to me.

Oh yeah, everything was balanced fine before starting.

Thanks for reading.

A choc chip cookie to anyone who knows the solution

Trev[/list]

Hi Trevor - as ever, this is general advice since I'm not familiar with the CG5GT...

1. Polar alignment (PA) and GOTO routines are normally seperate and you should view them as two distinct operations. That's not to say that PA will affect GOTO accuracy, but you can polar align without even thinking about GOTO...

2. I'd recommend forgetting the built in routine for polar alignment and go for the drift method. With the SAC 10 you'll find this a breeze (probably) and should be able to get PA good enough. The polar scope will get you close, but then do the drift. You'll get good PA within 20 mins.

3. As regards GOTO accuracy, that's down to the handset and its database and I'd be talking through my hat on that one...

4. I'm not sure what you mean by orthogonal in terms of an image, but another consideration is orthogonality of your OTA to the mount. If your OTA is not orthogonal (ie the mount axis and your optcal axis) are not aligned, you'll never achieve precise PA. But you can get close anough provided orthogonality is close enough... I couldn't possibly describe how to achieve orthogonality in a post but I have an Astrophysics routine that could help.

5. It seems that this mount gives all kinds of problems - and most seem routed in the software routines. If the motors are good and periodic error is low, you can pretty much forget software issues around PA and GOTO. Though I'm not sure if this mount requires you to go through the steps or if you can by-pass them...

Not sure if I deserve the choc chip cookie - yet...

Cheers

Dave

Thanks for the quick response Dave.

Periodic error on the CG5 is not meant to be great, but then again it's alot cheaper than most of the other mounts out there.
By orthogonal I really meant that those 25% of frames drifted about 90 degrees off in another direction.

Will try GuideDog tonight.

I was playing with Nebulosity and tried the Drizzle alignment instead of the standard one. Takes 6 or 7 times as long to stack but the results are extraordinary; It actually tightened up the tracking errors dramatically, even on 35 second exposures! What a fantastic program.

Thanks again for your help.

Trev

This link might help:

www.astronomyboy.com/cg5/

(The mount is known for a "hardening grease" problem):
.

it is still trailing at very low exposures and focal lengths, even after polar alignment.

Hi Trevor, I just got my cg5 goto mount only a few weeks back, and am experiencing the same problems, I can't even get a 30 second exposure with out trailing at nearly 90 degrees fro the direction the monut is supposed to be tracking :roll:

I too have tried everything dave has said here, but no joy, I spent many hours over the weekend trying my best, I've only had it out 5 times!!! and already it's gone.

Will try GuideDog tonight.

Wish I was that far, I'll go down this route too, but i can't offer any help I'm afraid, I'm too much of a newbie at this end of the game :oops:

Keith..

Trev,

I agree with Dave as to the accuracy of a polar alignment scope. I use the drift alignment method with my LXD75 SN-10 and it really works well for me. As to get your rig aligned to your mount may I suggest that you visit www.meade.com and download one of the SCT manuals? They illustrate the process in all their manuals and it is an easy process. They recommend doing it during the day, which makes it even easier. I can usually track without trails for up to two minutes and for longer exposures I use a 80mm guide scope. (piggyback) (If you want a more accurate drift alignment use a 2 or 3x on your final adjustments.

Good Luck,,,