AP 155 EDFS, AP rings on 16" Parallax Dovetail on Parallax 125 with
AP GTO.

I have had this out several times now and have been unable to get it
to point accurately - place and time setup are correct.

On calibrating with Polaris, I have used Pollux, but after several
iterations, whenever the mount slews back to Pollux, it is always off
by a couple of degrees and I have to push the East button to
re-center Pollux. When it slews to Polaris, Polaris will be centered.
When I slew to another object, I can find it by pressing the East
button for the same period of time.

I haven't checked for orthogonality using the method in the manual -
I don't know which stars straddling the meridian to use and I can't
stay up later to use Arcturus as per manual. On spec and assuming a
one degree error in orthogonality, I shimmed up the front rings by
one quarter inch tonight and it didn't seem to make any difference.

Even when I recalibrate on Pollux and then slew to Castor there is
still variable error of about half a degree.

Any ideas?

Mike Mah

Mike,

Check if the setting on your hand controller is for
the proper mount. On the AP mounts you can set up the
hand controller for the 400, 600, 900, and 1200
mounts. Choose the correct one for your mount.

Remove your shims.

Alternate method for Othogonality:

Do a star drift alignment, get alignment very
accurate, center a star on the same hour as Polaris,
calibrate with that star, and slew to 90 degrees Dec
and same hour angle, check if setting circles agree
with computer. Doing this should prevent a change in
RA when slewing, just incase something is wrong with
the RA. Insure that you are pointing exactly 90
degrees in dec. If unsure of the Dec, pick a star and
manually slew using the mechanical setting circles to
90 degrees.

Rotate Mount with RA only. Look using medium to high
power through the scope. The stars in the field should
rotate perfectly around centered of the field, if not
your orthogonality is off, you can shim either ring to
bring the orthogonality in. Remember, you must be
polar aligned, and be point perfectly 90 degrees Dec.

Now slew to a star, like Regulus, recalibrate on the
star. Try slewing to other stars to see if it is
pointing properly.

I hope this helps.

Tim


--- Mike Mah <mikemah@...> wrote:

AP 155 EDFS, AP rings on 16" Parallax Dovetail on
Parallax 125 with
AP GTO.

I have had this out several times now and have been
unable to get it
to point accurately - place and time setup are
correct.

On calibrating with Polaris, I have used Pollux, but
after several
iterations, whenever the mount slews back to Pollux,
it is always off
by a couple of degrees and I have to push the East
button to
re-center Pollux. When it slews to Polaris, Polaris
will be centered.
When I slew to another object, I can find it by
pressing the East
button for the same period of time.

I haven't checked for orthogonality using the method
in the manual -
I don't know which stars straddling the meridian to
use and I can't
stay up later to use Arcturus as per manual. On spec
and assuming a
one degree error in orthogonality, I shimmed up the
front rings by
one quarter inch tonight and it didn't seem to make
any difference.

Even when I recalibrate on Pollux and then slew to
Castor there is
still variable error of about half a degree.

Any ideas?

Mike Mah

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Hi Mike:

I just recently went through this with my 900 GTO mount so can offer a
couple of suggestions.

This is how I tried to align the mount and scope on Polaris, as suggested in
the AP manual that comes with the mount. After setting up the mount and
setting the Dec setting circle to 90 degrees I would look through the polar
alignment sight hole in the center of the polar axis to align on Polaris.
Then I would add the counterweight shaft and counterweights, and finally the
tube assembly. Each time I did this though I noted that OTA would be offset
slightly to the left or west of Polaris.

At first I thought that I had somehow shifted the mount a little when adding
the counterweights and tube assembly, so would just "pick up" (more like
nudge) the mount and scope until Polaris was aligned through the scope. But
I found that even after using the two star alignment method I would not end
up anywhere near the deep-sky object that I was trying to find using the GTO
feature.

So finally I looked through the polar alignment sight hole and to my
surprise Polaris was no where to be seen, even though it was still centered
in scope. At this point I figured the problem had to be that the rings were
not orthogonal with the mount. So off came the OTA and after checking the
rings realized they were fine. I then removed the ribbed mounting plate and
examined it to see if there could be a problem with it. It was fine too
however.

My next thought was that since I had used the used the scope and rings on my
home made Dob mount for the past four years that somehow I warped the rings
slightly (I rotate the rings on their sides and attach side bearings to
them; a photo of how they look is on my web page at
http://www.metro2000.net/~ericj, and click on Telescopes). I couldn't be
sure if this was a problem or not, and figured the only way to be sure was
to find another pair of AP mounting rings that would not be warped. Since I
have only had my 5.1" AP for less then a year I figured the likelihood that
these rings would be warped as the rings for the 7.1" were was unlikely.

So off came the 7.1" and rings, and on went the 5.1" and rings. Same
problem. Finally, I decided to look down the polar alignment sight hole from
the front to see if it looked aligned correctly. It didn't. With the setting
circle to 90 degrees the Dec axis seemed off to one side. I aligned it by
eye so that it appeared to be aligned correctly, and noted that the Dec
setting circle read 87 degrees. Back on went the 5.1" with rings, and this
time with the mount aligned on Polaris the scope was aligned on Polaris as
well.

Did the two star alignment method, but although the scope slewed closer to
the deep-sky object it still was off. So I finally tried using three star to
align the mount: Polaris, Vega, and Regulus. This time, the scope slewed to
M101 correctly, and with the high contrast of the 5.1" the galaxy was sharp,
well defined and surprisingly bright. Tried a few more objects and the
results were the same.

At this point, even though it was a during the work week, and it was almost
midnight, I couldn't resist the temptation of not using the 7.1". So off
came the 5.1" and on went the 7.1". This time I was even more careful when
aligning the mount, so I got to the point that I just left a 16mm Zeiss
eyepiece in the MaxBright when slewing from object to object and they were
often very close to the center of the FOV, which in the 16mm is around half
a degree or so. I finally got to bed around 2 AM, but it was worth it, even
though I dead tired the next day a work.

So I have a couple of suggestions for you. First, check to make sure that
the rings and OTA is orthogonal with the mount.

Second, check to see if, when looking down the front of the polar alignment
sight hole on your mount, if the Dec axis is centered or not. If not, you
cold have the same problem that I do. I have sent an e-mail to Marj and
mentioned it so she is aware of the situation. Whether yours has the same
problem or not I am not sure, but you can check.

Third, when you are doing you alignment do not use the N-S-E-W buttons to
recenter the star if it is off to one side. Use the altitude and azimuth
adjusters on your mount for this.

Fourth, try using three star rather then two.

Hope this helps. For what it is worth, I have found the 900 to be a very
fine and stable mount. I got into astronomy in the early 1970's, and got
quite use to star hopping to find deep-sky objects. When computer controlled
telescopes first came out I did not think I would ever want one. However,
since I have now had a chance to use the GTO feature I realize that there
are many deep-sky objects, like some of the fainter NGC or IC objects, that
will be much easier to find and observe now. So I look forward to many years
of finding and observing with my AP scopes and mounts.

Clear Skies,

Eric Jamison

Thanks for the tips Eric. You wrote:

I just recently went through this with my 900 GTO mount so can offer a
couple of suggestions.

----snip----

...so I got to the point that I just left a 16mm Zeiss
eyepiece in the MaxBright when slewing from object to object...

Using star diagonals (e.g., MaxBright) saves wear and tear on one's neck and
knees, but can introduce polar alignment errors. Be certain that the star
diagonal is dead-on in it's position within the 2" focuser tube; i.e., make sure
it is absolutely flush up against the focuser. Also make certain your ocular is
seated properly. Finally, be certain to use an ocular with cross-hairs.

Third, when you are doing you alignment do not use the N-S-E-W buttons to
recenter the star if it is off to one side. Use the altitude and azimuth
adjusters on your mount for this.

Just for clarification, don't use the N-S-E-W buttons to *recenter* Polaris.
One should use the buttons to center the other reference stars.

Larry Denmark
----
E-mail ..... kldenmark@...
Web site .. http://home.att.net/~kldenmark/

In a message dated 5/5/00 1:33:50 AM Mid-Atlantic Daylight Time,
ericj@... writes:

Fourth, try using three star rather then two.

Hi, I am very interested in this issue because I have the same problem with
my AP 600EGTO and cannot use polaris from my site. I've tried AP's two-star
alignment without success. Can you or anyone tell me where to find a
three-star alignment technique? I've never heard of that before. Does it
require polaris?

Peter

Thanks for the advice, everyone.

What is the three star alignment procedure? I don't recall seeing
this in the manual.

Mike Mah

--- In ap-gto@..., "ericj" <ericj@m...> wrote:

Hi Mike:

I just recently went through this with my 900 GTO mount so can

offer a

couple of suggestions.

This is how I tried to align the mount and scope on Polaris, as

suggested in

the AP manual that comes with the mount. After setting up the mount

and

setting the Dec setting circle to 90 degrees I would look through

the polar

alignment sight hole in the center of the polar axis to align on

Polaris.

Then I would add the counterweight shaft and counterweights, and

finally the

tube assembly. Each time I did this though I noted that OTA would

be offset

slightly to the left or west of Polaris.

At first I thought that I had somehow shifted the mount a little

when adding

the counterweights and tube assembly, so would just "pick up" (more

like

nudge) the mount and scope until Polaris was aligned through the

scope. But

I found that even after using the two star alignment method I would

not end

up anywhere near the deep-sky object that I was trying to find

using the GTO

feature.

So finally I looked through the polar alignment sight hole and to

my

surprise Polaris was no where to be seen, even though it was still

centered

in scope. At this point I figured the problem had to be that the

rings were

not orthogonal with the mount. So off came the OTA and after

checking the

rings realized they were fine. I then removed the ribbed mounting

plate and

examined it to see if there could be a problem with it. It was fine

too

however.

My next thought was that since I had used the used the scope and

rings on my

home made Dob mount for the past four years that somehow I warped

the rings

slightly (I rotate the rings on their sides and attach side

bearings to

them; a photo of how they look is on my web page at
http://www.metro2000.net/~ericj, and click on Telescopes). I

couldn't be

sure if this was a problem or not, and figured the only way to be

sure was

to find another pair of AP mounting rings that would not be warped.

Since I

have only had my 5.1" AP for less then a year I figured the

likelihood that

these rings would be warped as the rings for the 7.1" were was

unlikely.

So off came the 7.1" and rings, and on went the 5.1" and rings.

Same

problem. Finally, I decided to look down the polar alignment sight

hole from

the front to see if it looked aligned correctly. It didn't. With

the setting

circle to 90 degrees the Dec axis seemed off to one side. I aligned

it by

eye so that it appeared to be aligned correctly, and noted that the

Dec

setting circle read 87 degrees. Back on went the 5.1" with rings,

and this

time with the mount aligned on Polaris the scope was aligned on

Polaris as

well.

Did the two star alignment method, but although the scope slewed

closer to

the deep-sky object it still was off. So I finally tried using

three star to

align the mount: Polaris, Vega, and Regulus. This time, the scope

slewed to

M101 correctly, and with the high contrast of the 5.1" the galaxy

was sharp,

well defined and surprisingly bright. Tried a few more objects and

the

results were the same.

At this point, even though it was a during the work week, and it

was almost

midnight, I couldn't resist the temptation of not using the 7.1".

So off

came the 5.1" and on went the 7.1". This time I was even more

careful when

aligning the mount, so I got to the point that I just left a 16mm

Zeiss

eyepiece in the MaxBright when slewing from object to object and

they were

often very close to the center of the FOV, which in the 16mm is

around half

a degree or so. I finally got to bed around 2 AM, but it was worth

it, even

though I dead tired the next day a work.

So I have a couple of suggestions for you. First, check to make

sure that

the rings and OTA is orthogonal with the mount.

Second, check to see if, when looking down the front of the polar

alignment

sight hole on your mount, if the Dec axis is centered or not. If

not, you

cold have the same problem that I do. I have sent an e-mail to Marj

and

mentioned it so she is aware of the situation. Whether yours has

the same

problem or not I am not sure, but you can check.

Third, when you are doing you alignment do not use the N-S-E-W

buttons to

recenter the star if it is off to one side. Use the altitude and

azimuth

adjusters on your mount for this.

Fourth, try using three star rather then two.

Hope this helps. For what it is worth, I have found the 900 to be a

very

fine and stable mount. I got into astronomy in the early 1970's,

and got

quite use to star hopping to find deep-sky objects. When computer

controlled

telescopes first came out I did not think I would ever want one.

However,

since I have now had a chance to use the GTO feature I realize that

there

are many deep-sky objects, like some of the fainter NGC or IC

objects, that

will be much easier to find and observe now. So I look forward to

many years

of finding and observing with my AP scopes and mounts.

Clear Skies,

Eric Jamison

Mike Mah wrote:

What is the three star alignment procedure? I don't recall seeing
this in the manual.

Hi Mike:

I think I inadvertently created the "three star alignment procedure" :-). I
noticed the other night that after I had used the two star alignment
procedure (Polaris and Vega) when the scope slewed to a deep-sky object it
was not quite in the center of the field of view, even in a low power
eyepiece. On page 8 of the GTO Keypad Controller manual, items 7 through 14,
it recommends that using additional calibration stars to get a more accurate
polar alignment.

In my case after I used Regulus as my third calibration star (the "third"
star in my "three star alignment procedure") any deep-sky object that the
scope slewed to was near the center of the field of view of the 16mm Zeiss.
Normally when deep-sky observing I start off with a low power 2" eyepieces
like a 56mm Meade or 35mm Panoptic and work my up to higher power views
using the 1-1/4" eyepieces. But Sunday night it was late, I was tired, so I
just left the 16mm in. When AP comes out with the polar scope it should make
the whole polar alignment process much easier and faster.

I should mention that I have only had the mount for a short while, and only
had the chance to use it a few times, so am learning like everyone else.
Also, I did not mean to imply that the Dec setting circle on other AP GTO
mounts might be off slightly as mine was. I think I just happened to get one
that had this issue.

Clear Skies,

Eric Jamison

-----Original Message-----
From: Mike Mah <mikemah@...>
To: ap-gto@... <ap-gto@...>
Date: Friday, May 05, 2000 8:42 PM
Subject: Re: [ap-gto] Help with AP GTO on Parallax 125

Thanks for the advice, everyone.

What is the three star alignment procedure? I don't recall seeing
this in the manual.

Mike Mah

Peter wrote:

Can you or anyone tell me where to find a
three-star alignment technique? I've never heard of that before. Does it
require polaris?

Hi Peter:

Please see my response to Mike's question about the "three star alignment
procedure". I think I inadvertently created it :-). If you cannot use
Polaris from your site and the two-star alignment procedure isn't working
try using a third calibration star. It helped me to get accurate alignment.
Let us know how it goes.

Clear Skies,

Eric Jamison