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Adjusting the Polar Alignment Scope

Nels Johansen
 

Hi everyone,
I have been trying to adjust the Polar Alignment Scope, and I am having a disappointing result. After it is adjusted to the center, the reticule moves away from center after about 15 minutes of no activity, to where it was originally. Does anyone have ideas as to what is causing this?
Nels Johansen
 

Hi,

All of the optical polar alignment scopes, like the Losmandy one, or the Orion Atlas one, have a small diameter fragile, round glass plate, having the markings etched on (photo lithographed out of a Chrome metal layer, like used in the semiconductor industry for litho mask layers).

That small glass disk is held in place in the polar scope by 3 very tiny setscrews at 120 degree separation around the perimeter circle.??

The setscrews must not be screwed in tight on the glass, because the glass will chip, or worse, will crack.??

If one setscrew is very loose, the glass disk will move, just as you report.? So I think this is the cause of what you are seeing.? As the mount revolves in RA, gravity is shifting the glass "reticule" plate around until it falls on to the bottommost 2 setscrews.

Your job when setting up your polar scope is to very carefully:
1. Remove your scope and counterweights and counterweight shaft.
2.? Shift your DEC axis shaft til the scope porthole is fully open.?
3. Point your RA at a distant landmark point. I use a faraway treetop tip.??
4. Carefully tighten in a setscrew til the glass plate does not shift was you rotate the polar scope around in a circle.? Not too snug! Don't want to crack the reticule glass!
5. Look at the center cross or marker on the reticule. You want that center mark to remain
? ? a. Centered in the rotating reticule
? ? b. Move the AZ and Elevation to get that center for on the distant landmark point.?
6. To do that, you will have to:
? ? a. Loosen one setscrew
? ? b. Tighten one or both of the remaining setscrews.
7. Once you are done, the reticule is centered in the rotating RA axis shaft.? Leave the polar scope in place and/or mark it's orientation on the RA shaft. If you rotate that polar scope location, you will likely lose the centering of the reticule (because the machined RA axis is not perfect optically).
8. Now move your mount back to approximate polar alignment.??
9. Use a simulation of the Polar Scope View to know where Polaris should be seen through the polar scope. (The EQMOD software has a polar scope simulator for this.? Generally, Polaris is 180 degrees reverse from the sky she you'd see with Stellarium or other sky chart.)
10. Use the drift alignment method to perfect the RA alignment before deep sky imaging.??

(You might want to download and read the description of the polar scope adjustments in an Orion Atlas mount manual.)

Hope this helps,
Michael



On Fri, Jan 10, 2020, 1:33 PM Nels Johansen via Groups.Io <nhbj6=[email protected]> wrote:
Hi everyone,
I have been trying to adjust the Polar Alignment Scope, and I am having a disappointing result. After it is adjusted to the center, the reticule moves away from center after about 15 minutes of no activity, to where it was originally. Does anyone have ideas as to what is causing this?
Nels Johansen

 

¿ªÔÆÌåÓý

WHAT??

No PDF??

?

You feeling OK, Michael??

?

:-))

?

Derek

?

From: [email protected] [mailto:[email protected]] On Behalf Of Michael Herman
Sent: Friday, January 10, 2020 3:42 PM
To: [email protected]
Subject: Re: [Losmandy_users_io] Adjusting the Polar Alignment Scope

?

Hi,

?

All of the optical polar alignment scopes, like the Losmandy one, or the Orion Atlas one, have a small diameter fragile, round glass plate, having the markings etched on (photo lithographed out of a Chrome metal layer, like used in the semiconductor industry for litho mask layers).

?

That small glass disk is held in place in the polar scope by 3 very tiny setscrews at 120 degree separation around the perimeter circle.??

?

The setscrews must not be screwed in tight on the glass, because the glass will chip, or worse, will crack.??

?

If one setscrew is very loose, the glass disk will move, just as you report.? So I think this is the cause of what you are seeing.? As the mount revolves in RA, gravity is shifting the glass "reticule" plate around until it falls on to the bottommost 2 setscrews.

?

Your job when setting up your polar scope is to very carefully:

1. Remove your scope and counterweights and counterweight shaft.

2.? Shift your DEC axis shaft til the scope porthole is fully open.?

3. Point your RA at a distant landmark point. I use a faraway treetop tip.??

4. Carefully tighten in a setscrew til the glass plate does not shift was you rotate the polar scope around in a circle.? Not too snug! Don't want to crack the reticule glass!

5. Look at the center cross or marker on the reticule. You want that center mark to remain

? ? a. Centered in the rotating reticule

? ? b. Move the AZ and Elevation to get that center for on the distant landmark point.?

6. To do that, you will have to:

? ? a. Loosen one setscrew

? ? b. Tighten one or both of the remaining setscrews.

7. Once you are done, the reticule is centered in the rotating RA axis shaft.? Leave the polar scope in place and/or mark it's orientation on the RA shaft. If you rotate that polar scope location, you will likely lose the centering of the reticule (because the machined RA axis is not perfect optically).

8. Now move your mount back to approximate polar alignment.??

9. Use a simulation of the Polar Scope View to know where Polaris should be seen through the polar scope. (The EQMOD software has a polar scope simulator for this.? Generally, Polaris is 180 degrees reverse from the sky she you'd see with Stellarium or other sky chart.)

10. Use the drift alignment method to perfect the RA alignment before deep sky imaging.??

?

(You might want to download and read the description of the polar scope adjustments in an Orion Atlas mount manual.)

?

Hope this helps,

Michael

?

?

?

On Fri, Jan 10, 2020, 1:33 PM Nels Johansen via Groups.Io <nhbj6=[email protected]> wrote:

Hi everyone,
I have been trying to adjust the Polar Alignment Scope, and I am having a disappointing result. After it is adjusted to the center, the reticule moves away from center after about 15 minutes of no activity, to where it was originally. Does anyone have ideas as to what is causing this?
Nels Johansen

?

Virus-free.

Nels Johansen
 

Yes, I have done those things and am spinning the polar scope in v block and with the screws snug I can watch the center move in my target which is 30 feet away.? I just had a thought, there is what looks like a small amount of patroleum jelly around the edge under the keeper, perhaps the screws are not moving the reticule to a secure position but the screws are pushing against the resistance cause by the patroleum jelly.? Then as gravity pulls on the reticule it slides in its slot.
I have seen the instructions on the Company Seven website, I'll check out the Orian Atlas as well thanks.
Nels
 
Edited

Nels,

Are you having success with the alignment?? I have found that the inner lock ring, with two opposed slots, needs to be loosened before any set screws are turned.? The ring can be slightly loosened with a camera lens adjustable miniature spanner or a credit card cut to fit.? Take note; there is a small dab of thread lock holding the ring preventing rotation.? I use a wooden toothpick to apply a single drop of 99% alcohol multiple times over a period of two days to dissolve the thread lock.? Once free to rotate, I remove the ring and examine the setscrews (0.035"/0.9mm hex) that they are free to rotate while holding the tube vertical so as not to have the reticle drop out.? Should you remove the reticle, note the orientation of the locating ring that sits below the reticle.? Narrow/smaller dia. down.? If possible, do not remove the lock ring as it is difficult to rethread in the tube without cross threading the extremely fine threads.? So slightly loosen the lock ring then adjust setscrews.? After setscrew adjustment, and alignment is where you like it then rotate the lock ring snug not tight.? You may want to place a toothpick drop of nail polish at the rim of the lock ring.? I prefer not to as I will probably be making adjustments sooner than later.? Here is my suggestion as to the hex wrench to use....use a hex wrench such as a Wiha Tools with a cylindrical body...you can control the very light torque applied and use small pieces of colored tape to index mark the tool's body keeping track of the amount of the tool's rotation.
Nels Johansen
 

I have finally got it centered, it isn't that easy to do especially to remember which is up and down.? One frustration I have is when I remove the polar scope to and reinstall it doesn't remain centered. What am I doing wrong or is it the machining of the RA and clutch knob?
Nels
Sonny Edmonds
 
Edited

Hi Nels,
Any machinist will tell you that anytime a part is removed, it is a bugger to get it aligned again.
So for accuracy, especially repeat accuracy, don't dismount it.
I had a Polar Scope in my old mount. Used it a couple of times and decided it was not accurate enough for me.
 

¿ªÔÆÌåÓý

Nels, sonny's right about removing and reinstalling your Polar scope. I followed Michael Herman's, technique in zeroing my polar scope then I do a drift alignment ( a pain in the you know what) that is about as close to polar alignment I can get. This is okay for visual but probably not for long subs when imaging.I have not decided which system to go with Pole Master or Sharpcap.



Sent from my Galaxy Tab A



-------- Original message --------
From: "Nels Johansen via Groups.Io" <nhbj6@...>
Date: 1/29/20 4:58 PM (GMT-06:00)
Subject: Re: [Losmandy_users_io] Adjusting the Polar Alignment Scope

I have finally got it centered, it isn't that easy to do especially to remember which is up and down.? One frustration I have is when I remove the polar scope to and reinstall it doesn't remain centered. What am I doing wrong or is it the machining of the RA and clutch knob?
Nels

 
Edited

Why would you remove it? Just get it centered and leave it in place. No polar scope will get you really polar aligned, just good enough to do visual reliably. Another thing to know is your initial GOTOs will also not be very good without a good PA. This is adjusted once you do an initial alignment using the Gemini alignment routine but it will be off initially.? ?
--

Chip Louie - Chief Daydreamer Imagination Hardware
 

Nothing wrong with you... all GEM mounts have this polar scope shift issue.??

When you get your polar scope re-aligned, mark the rotation position of the polar scope in it's RA mounting tube, so you can get back to where you aligned it.? Even better, if possible, don't remove it.? Just rotate the RA axis to the right Polaris hour angle image (it is 180 degrees off from a sky chart view, due to the polar scope optics.)

The RA tubes are not perfect up the axis...and the polar scope is also slightly loose as it has to be to install it.? (That's why the video camera polar alignment approach has benefits...as you rotate the RA axis, it can determine the real center of rotation.)

Best,
Michael



On Wed, Jan 29, 2020, 2:58 PM Nels Johansen via Groups.Io <nhbj6=[email protected]> wrote:
I have finally got it centered, it isn't that easy to do especially to remember which is up and down.? One frustration I have is when I remove the polar scope to and reinstall it doesn't remain centered. What am I doing wrong or is it the machining of the RA and clutch knob?
Nels

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