Setting Circles

Hi,

I'm hoping someone out there can help me with a problem I'm having with
the setting circles on my telescope. I own a 4 1/2 inch Celestron Newtonian
with a German equatorial mount. Now because it's a starter scope, I never
expected the circles to be flawless. For starters, the circles are only
about 3 inches in diameter. That means the gradients are packed pretty
tight. And the needle marker is nice and fat which further compounds the
problem. But I'm wondering if there is something else I'm missing. Like when
I set the declination on Polaris, there is no problem. (In fact I don't have
any problem at all with declination. Whenever I put the scope on something
and check the declination, it's always correct.) But then I go to say,
Arcturus, and set the RA. When I test it out by going back to Polaris, it
puts me somewhere in the next county. Testing other objects leaves me
closer, but still with quite an error. I thought I'd be an eyepiece or two
away. Not 10 or 11 eyepieces away. I'm not even close. (I should also
mention that I'm using the outside numbers on the ring. The ones that
increase as I go from east to west. And also that the scope is level -
double and triple checked with a leveler. When I track an object, I only
have to move the RA axis.) The gradiants on the RA scale look evenly spaced.
How hard can it be to manufacture a circle with 24 evenly spaced hours and
10 minute intervals? I'm wondering if it's because maybe the distance
between RA lines decreases as you go to either celestial pole and increases
as you come back to the celestial equator. I thinking that manual setting
circles can't compensate for this. Maybe I should be setting the RA on a
star close to the nebula I want to go to and try from there rather than go
halfway across the sky which increases the error? Am I on the right track?
I'm thinking of upgrading to a Celestron 9 1/4 scope (not a goto) which also
has setting circles. But those circles, from looking at the picture, seem
smaller than what I have now. Does anyone out there have any experience with
a CG-5 mount from Celestron? Does anybody know of a good scope that comes
with good setting circles? I should add I'm not a goto type scope of person.
For me, half the fun is finding it myself. So I would rather take the money
spent on a goto and get more aperture. One last question that's been
bothering me. When my Newtonian is pointing at Polaris, because it's RA is
only one hour and something (I forget exactly here - I don't have my star
map) my scope's weight bar which holds the balancing weights should almost
be parallel to the ground, correct? Any help you can give me or web sites
that explain Newtonian German equatorial mount manual setting circles would
be appreciated. Thanks.


Steve




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In article , Steven Ziemba
wrote:
Hi,

I'm hoping someone out there can help me with a problem I'm having
with the setting circles on my telescope. I own a 4 1/2 inch Celestron
Newtonian with a German equatorial mount. Now because it's a starter
scope, I never expected the circles to be flawless. For starters, the
circles are only about 3 inches in diameter.

Forget the circles and learn the constellations. In my experience circles
are only of use with a computer controlled instrument.

Jochen

--

------------------------------------
If you like to learn about the Roe Valley
and some of its history, try:
http://www.jochenlueg.freeuk.com

In article , Steven Ziemba
wrote:
Hi,

I'm hoping someone out there can help me with a problem I'm having
with the setting circles on my telescope. I own a 4 1/2 inch Celestron
Newtonian with a German equatorial mount. Now because it's a starter
scope, I never expected the circles to be flawless. For starters, the
circles are only about 3 inches in diameter.

Forget the circles and learn the constellations. In my experience circles
are only of use with a computer controlled instrument.

Jochen

--

------------------------------------
If you like to learn about the Roe Valley
and some of its history, try:
http://www.jochenlueg.freeuk.com

Steven Ziemba wrote:

I'm hoping someone out there can help me with a problem I'm having with
the setting circles on my telescope.

[snip]

But then I go to say,
Arcturus, and set the RA. When I test it out by going back to Polaris, it
puts me somewhere in the next county. Testing other objects leaves me
closer, but still with quite an error.

As Jochen said, these small setting circles aren't much use. Beside
being coarsely graduated, they tend to slip on their axes when the
scope is slewed. But Polaris is in the worst possible location for
checking an RA setting; near the poles the meridians are all packed
close together as they converge. Set and test the RA circle on
objects with the lowest conveniently observable declination.

I thought I'd be an eyepiece or two
away. Not 10 or 11 eyepieces away. I'm not even close. (I should also
mention that I'm using the outside numbers on the ring. The ones that
increase as I go from east to west. And also that the scope is level -
double and triple checked with a leveler. When I track an object, I only
have to move the RA axis.)

That's the main thing! You may be doing as well as can be expected
with the setting circles if you can get within a few degrees.

--
Odysseus

Steven Ziemba wrote:

I'm hoping someone out there can help me with a problem I'm having with
the setting circles on my telescope.

[snip]

But then I go to say,
Arcturus, and set the RA. When I test it out by going back to Polaris, it
puts me somewhere in the next county. Testing other objects leaves me
closer, but still with quite an error.

As Jochen said, these small setting circles aren't much use. Beside
being coarsely graduated, they tend to slip on their axes when the
scope is slewed. But Polaris is in the worst possible location for
checking an RA setting; near the poles the meridians are all packed
close together as they converge. Set and test the RA circle on
objects with the lowest conveniently observable declination.

I thought I'd be an eyepiece or two
away. Not 10 or 11 eyepieces away. I'm not even close. (I should also
mention that I'm using the outside numbers on the ring. The ones that
increase as I go from east to west. And also that the scope is level -
double and triple checked with a leveler. When I track an object, I only
have to move the RA axis.)

That's the main thing! You may be doing as well as can be expected
with the setting circles if you can get within a few degrees.

--
Odysseus

Odysseus wrote in
:

Steven Ziemba wrote:

I'm hoping someone out there can help me with a problem I'm
having with the setting circles on my telescope.

[snip]

But then I go to say,
Arcturus, and set the RA. When I test it out by going back to Polaris,
it puts me somewhere in the next county. Testing other objects leaves
me closer, but still with quite an error.

As Jochen said, these small setting circles aren't much use. Beside
being coarsely graduated, they tend to slip on their axes when the
scope is slewed. But Polaris is in the worst possible location for
checking an RA setting; near the poles the meridians are all packed
close together as they converge. Set and test the RA circle on
objects with the lowest conveniently observable declination.

Steve, let me add that there is also the problem of time. If you have a
clock drive on your scope and it's engaged, then the RA circle should
stay accurate once you've set it using a known target. But if you don't
have a clock drive engaged, then you'll get an error that increases at 1
hour in RA per hour of ellapsed time after you set the circle using the
known target.

--
Steve Gray

Odysseus wrote in
:

Steven Ziemba wrote:

I'm hoping someone out there can help me with a problem I'm
having with the setting circles on my telescope.

[snip]

But then I go to say,
Arcturus, and set the RA. When I test it out by going back to Polaris,
it puts me somewhere in the next county. Testing other objects leaves
me closer, but still with quite an error.

As Jochen said, these small setting circles aren't much use. Beside
being coarsely graduated, they tend to slip on their axes when the
scope is slewed. But Polaris is in the worst possible location for
checking an RA setting; near the poles the meridians are all packed
close together as they converge. Set and test the RA circle on
objects with the lowest conveniently observable declination.

Steve, let me add that there is also the problem of time. If you have a
clock drive on your scope and it's engaged, then the RA circle should
stay accurate once you've set it using a known target. But if you don't
have a clock drive engaged, then you'll get an error that increases at 1
hour in RA per hour of ellapsed time after you set the circle using the
known target.

--
Steve Gray