Celestrom Goto problems/performance....

I'm a newbe to Astronomy.
I have a new Celestron C8-NGT.
It's an 8" newtonian on the Celestron GT mount.

I'm having problems with the goto....
My main question:
Am I expecting too much?
Or is my new Telescope broken?


I've tried aligning it several times.
The goto performance is just not very good.

Summary:
This is an equatorial mount.

The tripod is level and stable.

The telescope is balanced on both axis.

The telescope is powered with a large deep discharge 12V battery that
is freshly charged.

Today I bought the polar alignment scope accessory, so for tonight
I know I'm pointing north and have the right latitude equatorial mount
etc....

I'm using a GPS set to UTC for both lat,lon and time, so I know that
is good. UTC removes any time zone ambigiutiy.

I realize that for my location in CA the UTC time is usually the next
day and the scope is set apropriatly.


Star identification.....
I'm 95% certain I'm aligning to the starts the system suggests.

I'm aligning with the scope at ~ 200x so I'm setting things fine
enough.

Tonight the scope choose Vega as one of the alignment stars.
After alignment I goto mars, (Mars is not even in the spotter
scope!) thenI goto the Moon. (Almost full) again the moon is not in
the finder scope! I then tell it to go back to Vega, (One of the
origional alignment stars) It is barely in the finder scope!

My expectation was that the GOTO mount would do a reasonable job of
centering the desired object in the finder scope. I realize nothing is
perfect and you may have to do a little final tweaking.

Any suggestions?
Is my scope broken?
Am I stupid?
I've been operating under the assumption that I'm doing something
stupid for about 3 weeks now, but I'm starting to question the
equipment?


HELP!

Paul

I'm having problems with the goto....
My main question:
Am I expecting too much?

Hi Paul:

How does it do on stars and other non-planetary objects? If it's only bad on
planets, that would indicate problems with date and time.

Being "95% certain" about alignment stars just won't cut it. You need to be on
the correct stars every time. Usually if you're far off, you'll get "alignment
failure."

Make sure the telescope is well-balanced in RA and dec.

How are you centering the alignment stars? Your finder must be properly
aligned, so that you can be sure that you're centering the same star in a
medium power eyepiece that you've centered in the finder.

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

wrote in message
...

I've tried aligning it several times.
The goto performance is just not very good.

Summary:
This is an equatorial mount.

Good... Polar alignment may be critical, but if it aligns on 2 stars other
than Polaris, then polar alignment is probably not critical. The NexStars
use an algorithm that compensates for polar alignment error.

The tripod is level and stable.

Good... Leveling is not critical; stability is.

The telescope is balanced on both axes.

Good...

I'm using a GPS set to UTC for both lat,lon and time, so I know that
is good. UTC removes any time zone ambigiutiy.
I realize that for my location in CA the UTC time is usually the next
day and the scope is set apropriatly.

Good... Date, time, and location are not critical because the alignment
stars themselves tell the telescope where the sky is. However, date and
time are very important for finding planets.

Star identification.....
I'm 95% certain I'm aligning to the starts the system suggests.

Actually, I'm not; based on what you describe, I suspect you've
misidentified the alignment stars. Don't rely on the telescope to point at
them; use a star map and make sure.

I'm aligning with the scope at ~ 200x so I'm setting things fine
enough.

Good; centering the alignment star is critical.

Tonight the scope choose Vega as one of the alignment stars.
After alignment I goto mars, (Mars is not even in the spotter
scope!) thenI goto the Moon. (Almost full) again the moon is not in
the finder scope! I then tell it to go back to Vega, (One of the
origional alignment stars) It is barely in the finder scope!

Errors of several degrees or more... I'm thinking you've almost certainly
misidentified one of the alignment stars. What was the other star, the one
other than Vega?

With the nearly full moon in the sky, can you see enough of the surrounding
stars to be able to use a star map? If not, binoculars may help. Next to
Vega there is a fine double star (Epsilon Lyrae) visible in binoculars.
Actually Vega is pretty hard to miss, and it's more likely to be the other
star that was wrong.

(After nearly 40 years of observing, I am still occasionally bitten by
this -- I remember letting a telescope go to "Castor" which was actually
Pollux last year...)

Also, problems with Mars and especially the Moon could indicate a date/time
problem, because of orbital motion.

My expectation was that the GOTO mount would do a reasonable job of
centering the desired object in the finder scope. I realize nothing is
perfect and you may have to do a little final tweaking.

A reasonable expectation is for it to bring things within the field of a
25mm eyepiece. Yours isn't doing nearly that well, so some troubleshooting
is definitely in order!

There could conceivably be a mechanical problem causing slippage somewhere,
but let's double- and triple-check the star identification first.


--
Clear skies,

Michael Covington -- www.covingtoninnovations.com
Author, Astrophotography for the Amateur
and (new) How to Use a Computerized Telescope

Several more comments:

I aligned the finder and the main telescope on Mars, I know they are
both pointing at exactly the same place.

To be 100% certain I was using the proper alignment stars I
choose the three star alignment where I get to choose the stars.

I wanted to use Mizar, Vega and Arcturus.

So I found Mizar, easy to see as a double in the finder,
then also seen as a double at high magnification in the main scope. So
I'm sure it was Mizar.

Then Vega, 99.9% sure it was vega had a fainter double close by.


Lastly When I went to choose the third star from the list Arcturus was
not on the list, so for the third star I choose polaris, probably not
a great alignment star, but again I'm 100% sure of the identity.

After doing this I tried to GOTO back to the three alignment stars,
Vega, Mizar and Polaris, none of them was in the Finder scope.
All were close, but none were visable in the finder.

I was going to one more time, but it clouded up and I had to stop.

Tonight I'm going to print out star charts for the area close in to
all of the visible alignment stars and try one last time.

On the 20th I'm going to take the Scope to a star pary where maybe
I can get some help and have another set of eyes verify I'm not doing
something stupid.




On Mon, 8 Sep 2003 09:48:59 -0400, "Michael A. Covington"
wrote:


wrote in message
.. .

I've tried aligning it several times.
The goto performance is just not very good.

Summary:
This is an equatorial mount.

Good... Polar alignment may be critical, but if it aligns on 2 stars other
than Polaris, then polar alignment is probably not critical. The NexStars
use an algorithm that compensates for polar alignment error.

The tripod is level and stable.

Good... Leveling is not critical; stability is.

The telescope is balanced on both axes.

Good...

I'm using a GPS set to UTC for both lat,lon and time, so I know that
is good. UTC removes any time zone ambigiutiy.
I realize that for my location in CA the UTC time is usually the next
day and the scope is set apropriatly.

Good... Date, time, and location are not critical because the alignment
stars themselves tell the telescope where the sky is. However, date and
time are very important for finding planets.

Star identification.....
I'm 95% certain I'm aligning to the starts the system suggests.

Actually, I'm not; based on what you describe, I suspect you've
misidentified the alignment stars. Don't rely on the telescope to point at
them; use a star map and make sure.

I'm aligning with the scope at ~ 200x so I'm setting things fine
enough.

Good; centering the alignment star is critical.

Tonight the scope choose Vega as one of the alignment stars.
After alignment I goto mars, (Mars is not even in the spotter
scope!) thenI goto the Moon. (Almost full) again the moon is not in
the finder scope! I then tell it to go back to Vega, (One of the
origional alignment stars) It is barely in the finder scope!

Errors of several degrees or more... I'm thinking you've almost certainly
misidentified one of the alignment stars. What was the other star, the one
other than Vega?

With the nearly full moon in the sky, can you see enough of the surrounding
stars to be able to use a star map? If not, binoculars may help. Next to
Vega there is a fine double star (Epsilon Lyrae) visible in binoculars.
Actually Vega is pretty hard to miss, and it's more likely to be the other
star that was wrong.

(After nearly 40 years of observing, I am still occasionally bitten by
this -- I remember letting a telescope go to "Castor" which was actually
Pollux last year...)

Also, problems with Mars and especially the Moon could indicate a date/time
problem, because of orbital motion.

My expectation was that the GOTO mount would do a reasonable job of
centering the desired object in the finder scope. I realize nothing is
perfect and you may have to do a little final tweaking.

A reasonable expectation is for it to bring things within the field of a
25mm eyepiece. Yours isn't doing nearly that well, so some troubleshooting
is definitely in order!

There could conceivably be a mechanical problem causing slippage somewhere,
but let's double- and triple-check the star identification first.

wrote in message
...

After doing this I tried to GOTO back to the three alignment stars,
Vega, Mizar and Polaris, none of them was in the Finder scope.
All were close, but none were visable in the finder.

OK, you have some kind of mechanical slippage going on within the mount.
Time to contact the dealer and/or Celestron. Tell them I said so


--
Clear skies,

Michael Covington -- www.covingtoninnovations.com
Author, Astrophotography for the Amateur
and (new) How to Use a Computerized Telescope

wrote in message
...

After doing this I tried to GOTO back to the three alignment stars,
Vega, Mizar and Polaris, none of them was in the Finder scope.
All were close, but none were visable in the finder.

That's crucial. The error was 3 degrees or more. Normally, 0.25 degree
would be considered poor performance. Your mount is simply not working as
intended.

I wonder if he is aligning to North accurately? That can make a big
difference.

Phil

Michael A. Covington wrote:
wrote in message
...

After doing this I tried to GOTO back to the three alignment stars,
Vega, Mizar and Polaris, none of them was in the Finder scope.
All were close, but none were visable in the finder.


That's crucial. The error was 3 degrees or more. Normally, 0.25 degree
would be considered poor performance. Your mount is simply not working as
intended.

"Phil Wheeler" wrote in message
...
I wonder if he is aligning to North accurately? That can make a big
difference.

He said he used a polar alignment scope (I thought). Also, on a 3-star
alignment, the telescope should be able to calculate the polar alignment
error and allow for it. I have not actually used this model of telescope
and could be mistaken about that, but it's the way the newer ones work.

(Thank goodness. My classic LX200 requires perfect polar alignment in order
to have good pointing accuracy in equatorial mode.)

Michael A. Covington wrote:
"Phil Wheeler" wrote in message
...

I wonder if he is aligning to North accurately? That can make a big
difference.


He said he used a polar alignment scope (I thought). Also, on a 3-star
alignment, the telescope should be able to calculate the polar alignment
error and allow for it. I have not actually used this model of telescope
and could be mistaken about that, but it's the way the newer ones work.

(Thank goodness. My classic LX200 requires perfect polar alignment in order
to have good pointing accuracy in equatorial mode.)


I missed the original msg, alas. My NextStar 8 GPS (Alt-Az mode) makes
it pretty easy. But until I calibrated the built-in compass (finally
read the manual!) it was missing the alignment stars by a good bit,
almost as though it was pointing to magnetic north.

Phil

Paul,

I don't know if this will help, but the three dumbest things I have
done setting up a goto (on a 8i and a 114gt) a
1) setting time as am instead of pm
2) setting a coordinate as east instead of west (or n/s ... though you
said you had GPS - a good move).
3) not having the scope level and pointing north. I find I have
better luck using a compass as opposed to Polaris (I know, that makes
no sense, but my own experience, take it for what it is worth).

I have made all three at different times trying to rush through the
menu. One last one is taking to long to align a star.

Good luck with your scope. If you do take it to a star party, I am
sure someone will be able to sort things out. One last thing -- check
either the Celestron site or the nexstar site mentioned above. There
is a GPS software update for one version of the Nexstar.

Erik
socalsw

wrote in message . ..
Several more comments:

I aligned the finder and the main telescope on Mars, I know they are
both pointing at exactly the same place.

To be 100% certain I was using the proper alignment stars I
choose the three star alignment where I get to choose the stars.

I wanted to use Mizar, Vega and Arcturus.

So I found Mizar, easy to see as a double in the finder,
then also seen as a double at high magnification in the main scope. So
I'm sure it was Mizar.

Then Vega, 99.9% sure it was vega had a fainter double close by.


Lastly When I went to choose the third star from the list Arcturus was
not on the list, so for the third star I choose polaris, probably not
a great alignment star, but again I'm 100% sure of the identity.

After doing this I tried to GOTO back to the three alignment stars,
Vega, Mizar and Polaris, none of them was in the Finder scope.
All were close, but none were visable in the finder.

I was going to one more time, but it clouded up and I had to stop.

Tonight I'm going to print out star charts for the area close in to
all of the visible alignment stars and try one last time.

On the 20th I'm going to take the Scope to a star pary where maybe
I can get some help and have another set of eyes verify I'm not doing
something stupid.