First Telescope - On to Mounts

A different subject from my usual. This is based primarily on my
experience in my "First Telescopes - Experimentation" thread where a
borrowed a friends small GoTo telescope and had alignment headaches.
As you all know, I have no great need for GoTo but will get it if the
budget permits, largely because the difference between a dual axis
drive and GoTo looks to be under $150. In the discussions below, the
primary mounts I'm talking about are the ones that come with the GT
and non-GT versions of the Celestron Advanced series.

First, how I plan to use my telescope even if it has a GoTo mount. I
plan to find my star hopping, discovering on my own. Heck, I've found
with my binoculars that I frequently find interesting things in the
sky when I was looking for something else. Then I get the enjoyment
of trying to figure out what I'm looking at. To me, that is fun.

If I had a GoTo capable telescope, I would use it more at Star Parties
or public viewing events to quickly switch between objects that people
usually want to see or, for my own use, to quickly jump to my base
star on my star hopping journeys. I remember a Local Outreach event
to look at Saturn on 1/1 of this year. It was a cloudy night and one
guy had a 10 inch telescope with GoTo. He was rapidly able to
reposition when various targets appeared through the clouds while it
too the other people a bit longer. But, I'm moving off of my intended
subject rapidly now.

My real question here is mount alignment. To summarize what I think I
know:

Aligning a non-goto GEM mount: You level the tripod and then set the
rotational axis of the equatorial axis to point at the north star
(there appear to be nice spotter scopes that you can buy that fit into
the mount and make this a snap). Once you do this, the elevation
scale on the mount should match your latitude. If done accurately,
your equatorial axis should now be in plane with the celestial equator
and changes in this axis will be pure changes in RA. The declination
axis should move directly towards and away from the North Star. If
properly aligned, stars should stay centered in the eyepiece with only
adjustments to the RA axis (most planets will probably stay aligned as
well).

Now, I was reading some of the manuals for the various telescopes I'm
intending to buy and was confused about the alignment procedure for
the GoTo versions. These seem to be the same regardless of the mount
type (fork or GEM). They have easy align, 3 star align, 2 star align,
etc. No effort seems to be made to level or polar align the GEM's.
In addition, there is a separate polar alignment procedure that you
would do AFTER performing another alignment.

This seems inefficient to me. I realize that a computer (or a human
for that matter) can track an object using any 2 perpendicular axes.
However, the beauty of the GEM design is that you really only need one
motor (and thus less power required) if the mount is polar aligned
first. Am I missing something? Why don't you polar align the mount
first? Should I be doing it anyway?

Now, to really add to my confusion, I tried to look up how a GPS
receiver would help you out since these mounts have the capability to
accept one (hey, I'm an engineer). I figured that the GPS would give
a nice, accurate time (I realized how critical this was when I
borrowed the telescope) and position, but that you would still need to
align the telescope. Much to my surprise, it seems that the GPS
allows the computer to completely align and level the telescope
without any user input at all! Again, am I missing something and why
wouldn't you want to polar align the mount first?

Finally, a quick question that I'm a little confused about. Why do
you need to level the mount and then set the elevation scale on a GEM?
It seems to me that if you have the equatorial axis properly aimed at
the north star, you are aligned with the celestial axis and it
shouldn't matter if the base is absolutely level and the elevation is
set exactly to your latitude. I can see how leveling and using the
elevation scale might make the job of polar aligning easier,
especially if you don't have one of those neat little polar alignment
scopes, and I can see how it will make the base a little more stable
by more evenly distributing the weight on the tripod, but I don't see
how it is absolutely necessary. Again, am I missing something?

Thank you to everybody for your continued help. I'll be at a large
star party on Saturday and your responses have already given me a lot
to ask about and look at. I hadn't quite realized what a big jump
moving from Binoculars to a Telescope

On Thu, 29 Jan 2004 05:15:57 GMT, Edward Smith wrote:


Now, I was reading some of the manuals for the various telescopes I'm
intending to buy and was confused about the alignment procedure for
the GoTo versions. These seem to be the same regardless of the mount
type (fork or GEM). They have easy align, 3 star align, 2 star align,
etc. No effort seems to be made to level or polar align the GEM's.
In addition, there is a separate polar alignment procedure that you
would do AFTER performing another alignment.

This seems inefficient to me. I realize that a computer (or a human
for that matter) can track an object using any 2 perpendicular axes.
However, the beauty of the GEM design is that you really only need one
motor (and thus less power required) if the mount is polar aligned
first. Am I missing something? Why don't you polar align the mount
first? Should I be doing it anyway?

You do polar align a GEM first. If you align it very well, as you would for
doing imaging, all you need is a one-star alignment to sync the hour angle. But
if you aren't imaging, you don't need to be all that well polar aligned, so now
you need to do a two-star alignment if you want accurate gotos.


Now, to really add to my confusion, I tried to look up how a GPS
receiver would help you out since these mounts have the capability to
accept one (hey, I'm an engineer). I figured that the GPS would give
a nice, accurate time (I realized how critical this was when I
borrowed the telescope) and position, but that you would still need to
align the telescope. Much to my surprise, it seems that the GPS
allows the computer to completely align and level the telescope
without any user input at all! Again, am I missing something and why
wouldn't you want to polar align the mount first?

GPS gives you time and position. Some mounts also have an electronic compass and
a tilt sensor. All of that information is enough for the mount to roughly align
itself. You still need to align on a couple of reference stars, though. The
initial alignment is only good enough to allow the mount to point to those
alignment stars well enough that most people can find them easily.


Finally, a quick question that I'm a little confused about. Why do
you need to level the mount and then set the elevation scale on a GEM?
It seems to me that if you have the equatorial axis properly aimed at
the north star, you are aligned with the celestial axis and it
shouldn't matter if the base is absolutely level and the elevation is
set exactly to your latitude. I can see how leveling and using the
elevation scale might make the job of polar aligning easier,
especially if you don't have one of those neat little polar alignment
scopes, and I can see how it will make the base a little more stable
by more evenly distributing the weight on the tripod, but I don't see
how it is absolutely necessary. Again, am I missing something?

Nope, there is no need at all to level the mount (you don't even need to level
an altaz mount). Obviously, if an equatorial mount is off-level there will be a
certain amount of interaction between the altitude and azimuth adjustment
settings, but that will have an insignificant effect on the job of polar
alignment unless the tilt is severe. Just a casual leveling is more than
sufficient.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On Thu, 29 Jan 2004 05:15:57 GMT, Edward Smith wrote:


Now, I was reading some of the manuals for the various telescopes I'm
intending to buy and was confused about the alignment procedure for
the GoTo versions. These seem to be the same regardless of the mount
type (fork or GEM). They have easy align, 3 star align, 2 star align,
etc. No effort seems to be made to level or polar align the GEM's.
In addition, there is a separate polar alignment procedure that you
would do AFTER performing another alignment.

This seems inefficient to me. I realize that a computer (or a human
for that matter) can track an object using any 2 perpendicular axes.
However, the beauty of the GEM design is that you really only need one
motor (and thus less power required) if the mount is polar aligned
first. Am I missing something? Why don't you polar align the mount
first? Should I be doing it anyway?

You do polar align a GEM first. If you align it very well, as you would for
doing imaging, all you need is a one-star alignment to sync the hour angle. But
if you aren't imaging, you don't need to be all that well polar aligned, so now
you need to do a two-star alignment if you want accurate gotos.


Now, to really add to my confusion, I tried to look up how a GPS
receiver would help you out since these mounts have the capability to
accept one (hey, I'm an engineer). I figured that the GPS would give
a nice, accurate time (I realized how critical this was when I
borrowed the telescope) and position, but that you would still need to
align the telescope. Much to my surprise, it seems that the GPS
allows the computer to completely align and level the telescope
without any user input at all! Again, am I missing something and why
wouldn't you want to polar align the mount first?

GPS gives you time and position. Some mounts also have an electronic compass and
a tilt sensor. All of that information is enough for the mount to roughly align
itself. You still need to align on a couple of reference stars, though. The
initial alignment is only good enough to allow the mount to point to those
alignment stars well enough that most people can find them easily.


Finally, a quick question that I'm a little confused about. Why do
you need to level the mount and then set the elevation scale on a GEM?
It seems to me that if you have the equatorial axis properly aimed at
the north star, you are aligned with the celestial axis and it
shouldn't matter if the base is absolutely level and the elevation is
set exactly to your latitude. I can see how leveling and using the
elevation scale might make the job of polar aligning easier,
especially if you don't have one of those neat little polar alignment
scopes, and I can see how it will make the base a little more stable
by more evenly distributing the weight on the tripod, but I don't see
how it is absolutely necessary. Again, am I missing something?

Nope, there is no need at all to level the mount (you don't even need to level
an altaz mount). Obviously, if an equatorial mount is off-level there will be a
certain amount of interaction between the altitude and azimuth adjustment
settings, but that will have an insignificant effect on the job of polar
alignment unless the tilt is severe. Just a casual leveling is more than
sufficient.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On Thu, 29 Jan 2004 05:15:57 GMT, Edward Smith wrote:


Now, I was reading some of the manuals for the various telescopes I'm
intending to buy and was confused about the alignment procedure for
the GoTo versions. These seem to be the same regardless of the mount
type (fork or GEM). They have easy align, 3 star align, 2 star align,
etc. No effort seems to be made to level or polar align the GEM's.
In addition, there is a separate polar alignment procedure that you
would do AFTER performing another alignment.

This seems inefficient to me. I realize that a computer (or a human
for that matter) can track an object using any 2 perpendicular axes.
However, the beauty of the GEM design is that you really only need one
motor (and thus less power required) if the mount is polar aligned
first. Am I missing something? Why don't you polar align the mount
first? Should I be doing it anyway?

You do polar align a GEM first. If you align it very well, as you would for
doing imaging, all you need is a one-star alignment to sync the hour angle. But
if you aren't imaging, you don't need to be all that well polar aligned, so now
you need to do a two-star alignment if you want accurate gotos.


Now, to really add to my confusion, I tried to look up how a GPS
receiver would help you out since these mounts have the capability to
accept one (hey, I'm an engineer). I figured that the GPS would give
a nice, accurate time (I realized how critical this was when I
borrowed the telescope) and position, but that you would still need to
align the telescope. Much to my surprise, it seems that the GPS
allows the computer to completely align and level the telescope
without any user input at all! Again, am I missing something and why
wouldn't you want to polar align the mount first?

GPS gives you time and position. Some mounts also have an electronic compass and
a tilt sensor. All of that information is enough for the mount to roughly align
itself. You still need to align on a couple of reference stars, though. The
initial alignment is only good enough to allow the mount to point to those
alignment stars well enough that most people can find them easily.


Finally, a quick question that I'm a little confused about. Why do
you need to level the mount and then set the elevation scale on a GEM?
It seems to me that if you have the equatorial axis properly aimed at
the north star, you are aligned with the celestial axis and it
shouldn't matter if the base is absolutely level and the elevation is
set exactly to your latitude. I can see how leveling and using the
elevation scale might make the job of polar aligning easier,
especially if you don't have one of those neat little polar alignment
scopes, and I can see how it will make the base a little more stable
by more evenly distributing the weight on the tripod, but I don't see
how it is absolutely necessary. Again, am I missing something?

Nope, there is no need at all to level the mount (you don't even need to level
an altaz mount). Obviously, if an equatorial mount is off-level there will be a
certain amount of interaction between the altitude and azimuth adjustment
settings, but that will have an insignificant effect on the job of polar
alignment unless the tilt is severe. Just a casual leveling is more than
sufficient.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

This seems inefficient to me. I realize that a computer (or a human
for that matter) can track an object using any 2 perpendicular axes.
However, the beauty of the GEM design is that you really only need one

Hi:

Polar alignment has little effect on goto. But it WILL effect how well the
scope tracks when a goto is complete. The only time a goto scope will be driven
in declination/altitude is when you're talking about a goto fork mount that is
set-up in alt-az mode. No current goto GEM scope is driven in declination, so
it must be decently aligned for good tracking.

As for GPS, it can help speed the alignment process, but user intervention is
still required to center alignment stars. Actually, the GPS provides ONLY time
and position. An internal compass and level switches/sensors allow the scope to
orient itself.

You _can_ polar align the scope first. I think what's getting you confused is
"alignment." Look upon _polar_ alignment and _goto_ alignment as two somewhat
related but distinct processes. Generally, with a GEM, it's a good idea to do a
rough polar alignment first, do a goto alignment, and then a finer polar
alignment, either using the built in routine that some of these scopes feature
or a drift alignment.

Generally levelling is not very important. In some cases with some goto mounts
it can help put the alignment stars (for goto) closer initially, but once
alignment is done, it really has no effect.


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

This seems inefficient to me. I realize that a computer (or a human
for that matter) can track an object using any 2 perpendicular axes.
However, the beauty of the GEM design is that you really only need one

Hi:

Polar alignment has little effect on goto. But it WILL effect how well the
scope tracks when a goto is complete. The only time a goto scope will be driven
in declination/altitude is when you're talking about a goto fork mount that is
set-up in alt-az mode. No current goto GEM scope is driven in declination, so
it must be decently aligned for good tracking.

As for GPS, it can help speed the alignment process, but user intervention is
still required to center alignment stars. Actually, the GPS provides ONLY time
and position. An internal compass and level switches/sensors allow the scope to
orient itself.

You _can_ polar align the scope first. I think what's getting you confused is
"alignment." Look upon _polar_ alignment and _goto_ alignment as two somewhat
related but distinct processes. Generally, with a GEM, it's a good idea to do a
rough polar alignment first, do a goto alignment, and then a finer polar
alignment, either using the built in routine that some of these scopes feature
or a drift alignment.

Generally levelling is not very important. In some cases with some goto mounts
it can help put the alignment stars (for goto) closer initially, but once
alignment is done, it really has no effect.


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

This seems inefficient to me. I realize that a computer (or a human
for that matter) can track an object using any 2 perpendicular axes.
However, the beauty of the GEM design is that you really only need one

Hi:

Polar alignment has little effect on goto. But it WILL effect how well the
scope tracks when a goto is complete. The only time a goto scope will be driven
in declination/altitude is when you're talking about a goto fork mount that is
set-up in alt-az mode. No current goto GEM scope is driven in declination, so
it must be decently aligned for good tracking.

As for GPS, it can help speed the alignment process, but user intervention is
still required to center alignment stars. Actually, the GPS provides ONLY time
and position. An internal compass and level switches/sensors allow the scope to
orient itself.

You _can_ polar align the scope first. I think what's getting you confused is
"alignment." Look upon _polar_ alignment and _goto_ alignment as two somewhat
related but distinct processes. Generally, with a GEM, it's a good idea to do a
rough polar alignment first, do a goto alignment, and then a finer polar
alignment, either using the built in routine that some of these scopes feature
or a drift alignment.

Generally levelling is not very important. In some cases with some goto mounts
it can help put the alignment stars (for goto) closer initially, but once
alignment is done, it really has no effect.


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

Polar alignment has little effect on goto. But it WILL effect

"affect" ;-)

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

Polar alignment has little effect on goto. But it WILL effect

"affect" ;-)

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

Polar alignment has little effect on goto. But it WILL effect

"affect" ;-)

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