horrible night with my CG5-GT

[michigander]

Finally got a clear night when I didn't have to be up at 5am the next morning and was looking forward to trying my new LP filter (thanks FLO).

Chose to do 2 star align and asked it to go to Arcturus. Scope ended up about 30 degrees off, so I slewed to it with the hand control. Spica was the next target; a little closer, but still way off. Slewed to it and hit Align. Success, it said.

Punched in M13 and as the scope slewed it made contact with the tripod leg and stopped. Blooody hell.

Started alignment again. Used Arcturus and Alcor this time. still had to manually slew 20 or 30 degrees to get them. Align success, again. Punch in M13. This time it ends up pointing almost due south and somewhat below the horizon!

Went through the alignment procedure two more times before giving up in disgust. I was ready to break something by then.

I can't get a perfect polar alignment from my back garden as the house is in the way; but it's never been a problem before. I'm sure it's within a degree or two.

I searched the forum and found an old post from James that said

"The other thing to consider is that the mount remembers its Home position (usually with the index marks aligned). If you manually release the clutches and move the scope then it will get confused next time. You will need to enter everything correctly then slew the scope to the alignment stars using the handset. Once done correctly the next time you align it should be a much quicker experience"

I DID release the clutches after the scope contacted the tripod leg, but shut everything off and reset the index marks before starting over.

Any ideas? I really miss my old Dob right now!

Dana

[arad85]

Goto accuracy on the GT5 seems to be a function of balancing the scope on the mount too. I had mine spot on perfect for Saturday night - everything bang on into the centre of the eyepiece on every goto. Sunday, I tried 2-star aligning half a dozen times and it was way out (although not 20 or 30 degrees). Checked the scope balance and it was out. Moved one of the weights and it was better, although still not perfect. Gave up at that point - we had visitors around and I'd shown them a few fuzzies so it had served it's purpose

HTH...

[Deneb]

from the times that I have been out this month, I have managed to do 3 star alignments - Arcturus from the South, 2nd Dubhe in Ursa Major & 3rd Vega in Lyra. Just make sure your time settings & location are Correct, polar align the scope & level the mount/tripod then try to align from the South first.

[BlueAstra]

I had a problem like this once with my simple mount, and it turned out to be that I had entered the wrong date. It used US format rather than UK date format, and although I'd done it many times before, I got it wrong. So advice to check time and date is good (and daylight saving on).

[arad85]

I had a problem like this once with my simple mount, and it turned out to be that I had entered the wrong date. It used US format rather than UK date format, and although I'd done it many times before, I got it wrong. So advice to check time and date is good (and daylight saving on).

It's not that easy to get it the wrong way around when the date is after the 12th of the month

[James]

Have a look at the Celestron_AS Yahoo Group, specifically their FAQs file - it has a wealth of information about the CG5-GT mount which I found helpful with my mount.

I had a whole string of strange niggles with my CG5-GT and pretty much all of them were solved with info from that site. The CG5-GT is a great mount (aside perhaps for the noisy motors )

James

[michigander]

Thanks guys!

I think Arad85 may have identified the problem. I sometimes balance the scope when I take it out, but didn't last night. I think it may have been 'front heavy'.

Now if we can just get another clear night I'll take his advice.

James- Thanks for the link. It's gone into my Favorites.

Dana

[arad85]

Chose to do 2 star align and asked it to go to Arcturus. Scope ended up about 30 degrees off, so I slewed to it with the hand control. Spica was the next target; a little closer, but still way off. Slewed to it and hit Align. Success, it said.

Punched in M13 and as the scope slewed it made contact with the tripod leg and stopped. Blooody hell.

Think I may have solved this one. I was having EXACTLY the same symptoms tonight. I know the mount is levelled and I'm pretty meticulous about getting the polar alignment sorted too.

Tried aligning to Arcturus, about 30 degrees too far south and a little east too. Switched off the mount, rebalanced it and put it back at starting point and repowered. Entered/checked date and time - all perfectly fine, align to Arcturus again and it's pointing at exactly the same spot again, way off Arcturus...

A couple of resets later, after mobving weights etc around each time with the mount just repeating the slews, I thought lets try aligning all the way through. Arcturus, wayyy off - centred and aligned it. Then chose Phad. Way off again, but I slewed and aligned.

Then it asks for a calibration star - added Vega. Again, slewed wayyy off but aligned it as per usual. Thought I'd try adding a second calibration star - deneb... asked it to goto and it was within the 6x30 finderscope - in fact about 1/3 of the way from the centre. Centred and aligned. Then thought I'd add a third calibration star - Rasalgethi. Enter it's name and away it goes - only to place the star BANG slap in the middle of the finderscope. Aligned and added it.

Then chose M3 and hit enter and slap in the centre of the viewfinder.

The key appears to be giving it 3+ stars to align to. I know that when I set the scope up on Saturday, I added at least 1 if not 2 calibration stars. Not sure how many I added Sunday, probably one or none as I was in a hurry. I know there should only be a need for a single pair of calibration stars (you have a known 3rd point - your location and time, so everything else is calculable) but it appears more alignment stars makes it much more accurate. Also, the satars I choose from the West are very high in the sky - Arcturus had only just transited when I used it as a star - and that may mean the maths is more prone to error.

Tonight everything was repeatable - initial slews even after moving weights - sometimes quite radically and resetting the mount were all in the same general direction. Although I didn't realign after the session, I'm pretty confident that next time it's way off, adding a couple of calibration stars will sort it out.

Hope that helps.

[michigander]

Thanks arad!

It tough for me to get 3 calibration stars from my back garden. I have a limited FOV; nothing to the north, trees blocking 30 degrees of the southern horizon and another big tree in the southeast. And it doesn't help that the CG5 only lists the Arabic names. Don't know why they can't give the Greek designation. I know the Arabic names of the brightest stars, but have never heard of half of the ones on their list and there's no point in calibrating on something I'm not sure of. I'll have to find a cross-reference list of some sort.

Still hoping that I didn't have the scope balanced properly. I had noticed that the drive sounded like it was laboring, and at one point I was aware that it wasn't balanced, but was too [removed word] off at the time to realize that that might be the problem.

Will have to wait until Sunday night to try again; good ol' 14 hour shifts this weekend...

Thanks again.

Dana

[arad85]

Thanks arad!

No problems - glad to have understood it myself - was getting very annoyed

It tough for me to get 3 calibration stars from my back garden. I have a limited FOV; nothing to the north, trees blocking 30 degrees of the southern horizon and another big tree in the southeast. And it doesn't help that the CG5 only lists the Arabic names. Don't know why they can't give the Greek designation. I know the Arabic names of the brightest stars, but have never heard of half of the ones on their list and there's no point in calibrating on something I'm not sure of. I'll have to find a cross-reference list of some sort.

He he... and who says having a goto mount means you don't learn to navigate your way around the sky!!

Still hoping that I didn't have the scope balanced properly. I had noticed that the drive sounded like it was laboring, and at one point I was aware that it wasn't balanced, but was too [removed word] off at the time to realize that that might be the problem.

Will have to wait until Sunday night to try again; good ol' 14 hour shifts this weekend...

Thanks again.

Dana

Try using stars that are as far away from the meridian as possible. Thinking about the problem again, if you are using stars that are nearly overhead, even a small error may cause big problems. The other thing I learned last night is that although the controller starts to find alignment stars in the West, you can change this to stars in the East by pressing the MENU button when you are doing the alignment.

Enjoy your shifts