GOTO gone AWOL

[broadsword]

Being fairly new to astronomy I have struggled with a number of things, but one thing that has always been OK for me has been the GOTO on my mounts. Not tonight though, on what looked to be a perfect night for imaging. Having polar aligned my NEQ6 PRO as usual, and then successfully carried out a 1-star alignment I was finding my objects fine, but then suddenly everything seemed to be getting missed. I switched off and started alignment again (using 3-star this time) but everything seemed some way off - about 2/3 of the way across the finder scope from the cross hair, and always in the same (left, horizontal) direction, with Alignemt failed being the result. I re-checked polar alignemnt and repeated the whole thing about four times, always with the same (almost systematic) degree of error. Then gave up and came inside.

I'm hoping when I next try the whole thing has gone away, but has anyone had a similar experience/got any advice?

[broadsword]

Didn't get any replies to this, so just adding this comment to return it back to the top of the list! Really hoping for any advice, as I'm away in Switzerland on business and want to try and sort out the problem and not lose another precious clear night when I return............

[cantharis]

Are you sure your power supply is good? Dodgy supplies are a major source of problems with GOTO mounts.

[perfrej]

The problem is usually one (or both) of these:

1. Time

You have to consider the fact that one second error in the time keeping in your mount controller will offset Ra by 15 arc-seconds. 4 seconds off means a full arc-minute! Make sure you set the time to the second!

2. Your home position

How on earth are you going to be able to set your mount to the home position with any precision? Well, you can't. But there is a sneak trick that you can adapt and always get the proper home position - perfectly!

Alignment procedure with perfect home position. This assumes reasonable polar aligned by means of the polar scope and - very important - very well leveled mount.

1. Power off mount

2. Loosen clutches and try to get a reasonably good home position. Tighten cutches.

3. Power on mount and enter accurate time (again, very accurate time is needed).

4. Initiate a three star align and let it slew to where it thinks the first star is.

5. Do not touch the keypad now! Instead, loosen clutches slightly and nudge the star into the cross hair of your finder by pushing the scope carefully, then some more to get it to the middle of the eye-piece (or CCD if you're like me and never had an eye-piece). Tighten clutches.

6. Press enter on your keypad to accept the first star, then slew to the next.

7. Center with keypad, enter and repeat for third star.

Now, if you park your scope. You'll see it goes to a perfect home position. Actually, the procedure can be aborted after you nudged the first star by hand - that is what produces the home position. After you have a good home position, you can perform any alignment and you will find that there is very little to adjust for each alignment star. And, remember that once you have your home position hand adjusted you don't need to do it agian, so should you power off the mount (parked) and then power on after a while there is no need to redo the nudge.

Next thing you will want to do is get a mount with encoders No home problem, can be powered off in any position and hand moved anywhere and still retains perfect alignment.

So, try the above and become a happy camper

/per

[broadsword]

Are you sure your power supply is good? Dodgy supplies are a major source of problems with GOTO mounts.

Yes, I thought of this, as my power connector into the mount sometimes comes half out. However, I don't think it was power related as I repeated the whole set up about four times, and each time the degree of error was the same - hence it looked more like a systematic error, the sort of thing you get if you put the wrong time or date into the GOTO (which I've done many times) - nothing is where it is meant to be accoridng to the mount computer!

Looks like a good night tonight, so I'm just hoping it doesn't reappear......

[broadsword]

The problem is usually one (or both) of these:

1. Time

You have to consider the fact that one second error in the time keeping in your mount controller will offset Ra by 15 arc-seconds. 4 seconds off means a full arc-minute! Make sure you set the time to the second!

2. Your home position

How on earth are you going to be able to set your mount to the home position with any precision? Well, you can't. But there is a sneak trick that you can adapt and always get the proper home position - perfectly!

Alignment procedure with perfect home position. This assumes reasonable polar aligned by means of the polar scope and - very important - very well leveled mount.

1. Power off mount

2. Loosen clutches and try to get a reasonably good home position. Tighten cutches.

3. Power on mount and enter accurate time (again, very accurate time is needed).

4. Initiate a three star align and let it slew to where it thinks the first star is.

5. Do not touch the keypad now! Instead, loosen clutches slightly and nudge the star into the cross hair of your finder by pushing the scope carefully, then some more to get it to the middle of the eye-piece (or CCD if you're like me and never had an eye-piece). Tighten clutches.

6. Press enter on your keypad to accept the first star, then slew to the next.

7. Center with keypad, enter and repeat for third star.

Now, if you park your scope. You'll see it goes to a perfect home position. Actually, the procedure can be aborted after you nudged the first star by hand - that is what produces the home position. After you have a good home position, you can perform any alignment and you will find that there is very little to adjust for each alignment star. And, remember that once you have your home position hand adjusted you don't need to do it agian, so should you power off the mount (parked) and then power on after a while there is no need to redo the nudge.

Next thing you will want to do is get a mount with encoders No home problem, can be powered off in any position and hand moved anywhere and still retains perfect alignment.

So, try the above and become a happy camper

/per

Hi Per,

This has got me thinking!!

I have been guessing the time a bit as my digital watch is about 30 seconds slow whan I check it accurately, so I've been adding number this routinely. I'm probably adding a systematic error then of at least a few seconds.....didn't realise it made this much difference.

I really like the technique for getting perfect home position, I must admit I always thought it was a bit hit and miss. I shall try this out tonight!

As you seem to be mount focused, one other question was bothering me. I usually manage to polar align OK these days (I'm a relative beginner to this), but I find that the pointer on the mount is indicating an angle of altitude for Polaris which is about 2-3 degrees less than my geographical home latitude. It hasn't caused a problem in the past, so I ignored it, thought it was maybe just a crude dial on the mount...

[perfrej]

I'd say crude dial on the mount. The thing is glued on with no accurate reference point. I recall mine was way off too.

/per

[broadsword]

Per,

Tried your home-finding position method last night and it woked fantastically, got me back to the best I've had. Also finally started putting the time into the GOTO to the nearest second.

And then, half way through a 40 minute imaging run, the mount stopped, probably due to the power lead slipping. So backs up Cantharis's point as well!

[perfrej]

Great news, Neil!

So, just stay away from the power cords and you should be all set for a long winter of exposure!

/per

[cantharis]

I usually manage to polar align OK these days (I'm a relative beginner to this), but I find that the pointer on the mount is indicating an angle of altitude for Polaris which is about 2-3 degrees less than my geographical home latitude.

I am amazed that you can read that blunt pointer that accurately !!!!