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CGX-L index Mark's on the mount?

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#1 Koinonos

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Posted 27 January 2020 - 12:35 AM

I just moved up to a CGX-L from a CGEM DX mount and am noticing that there are no alignment or index markers so that the mount is starting with minimal DEC or RA misalignment before turning on the telescope.

What techniques are fellow CGX-L users using to simulate the physical index markers on the mount like the CGEM's have?  Are you using a level and then using a white marker or tape to make your own index marks?

 

I was trying manually center Polaris in the OTA view and noticed that when I turned the attitude adjustment knob, Polaris instead of vertically rising or lowering was actually moving laterally as well!  When I turned on my red light headlight and looked I could see that the OTA was not facing directly forwards and the tube itself was leaning to the right a little. Mea Culpa..

 

Had their been alignment markers that 45 minutes of frustration could have easily been avoided. So how are my fellow CGX-L drivers making sure that the mount is physically aligned correctly before you turn on the mount to start to align to Polaris at the home position?

Kind Regards,
Koinonos


Edited by Koinonos, 27 January 2020 - 12:58 AM.


#2 freestar8n

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Posted 27 January 2020 - 01:07 AM

The CGX-L has homing switches.  There is no need for index marks.  If you use the handcontrol or cpwi it doesn't matter how the mount is oriented when you start up.  It will ask to go to the homing switches and that sets the dec. and ra. reference locations.  It should be much more accurate than manually aligning on index marks.

 

Frank



#3 Koinonos

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Posted 27 January 2020 - 01:13 AM

Thanks Freestar8n, I have the Celestron manual loaded up and browsing through it for 'homing' or homing switches and 0 entries come up when I seach the PDF.  Can you point me to which page of the manual you are referring to accomplish this?  I don't want to mess this up. 

 

I want to get my mount such that when I adjust the attitude adjustment knob Polaris only moves vertically like it does on my CGEM DX mount, and not vertical + sideways which means my mount is off-axis physically even with level bubbles dead center.

 

Thanks!


Edited by Koinonos, 27 January 2020 - 01:13 AM.


#4 freestar8n

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Posted 27 January 2020 - 01:20 AM

Look for "Home Position" or "home switch position."

 

https://s3.amazonaws...l_5lang_Web.pdf

 

I actually don't know how you used the mount at all without finding the switches...

 

 

 

The mount’s internal switches will take the mount to its home position when you power it on

 

Frank



#5 Koinonos

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Posted 27 January 2020 - 01:46 AM

I am just starting with this mount. 

 

That is why I am asking these questions of fellow CGX-L owners since the mount's manual appears to suffer from selection effect, where it is written assuming you already know this mount.  I think it is missing the answer to a key question:

 

When you turn the mount on and go to home via the Enter key, what should be in the OTA at the default home position?  Polaris?

 

  • According to the manual when you turn it on and press Enter twice the mount is supposed to move itself to the Home position where I assume it has internal markers to calculate 0 degrees RA and 0 degrees DEC.

 

  • The manual doesn't state so on p. 10. But if Polaris is not dead center when you go to the home position where the controller reads 0 degrees RA and 0 degrees DEC, I infer that is the time to loosen the clutches and manually put Polaris dead center in RA, DEC, and the attitude knob?

 

Kind Regards,

Koinonos

 

 


Edited by Koinonos, 27 January 2020 - 02:26 AM.


#6 Glass Eye

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Posted 27 January 2020 - 08:26 AM


I am just starting with this mount. 

 

That is why I am asking these questions of fellow CGX-L owners since the mount's manual appears to suffer from selection effect, where it is written assuming you already know this mount.  I think it is missing the answer to a key question:

 

When you turn the mount on and go to home via the Enter key, what should be in the OTA at the default home position?  Polaris?

 

  • According to the manual when you turn it on and press Enter twice the mount is supposed to move itself to the Home position where I assume it has internal markers to calculate 0 degrees RA and 0 degrees DEC. Yes! The mount has zero switches for RA and DEC.

 

  • The manual doesn't state so on p. 10. But if Polaris is not dead center when you go to the home position where the controller reads 0 degrees RA and 0 degrees DEC, I infer that is the time to loosen the clutches and manually put Polaris dead center in RA, DEC, and the attitude knob? No! Do not loosen the clutches.  There are adjustment screws for the RA and DEC.

 

Kind Regards,

Koinonos



#7 archer1960

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Posted 27 January 2020 - 11:53 AM

I am just starting with this mount. 

 

That is why I am asking these questions of fellow CGX-L owners since the mount's manual appears to suffer from selection effect, where it is written assuming you already know this mount.  I think it is missing the answer to a key question:

 

When you turn the mount on and go to home via the Enter key, what should be in the OTA at the default home position?  Polaris?

 

  • According to the manual when you turn it on and press Enter twice the mount is supposed to move itself to the Home position where I assume it has internal markers to calculate 0 degrees RA and 0 degrees DEC.

 

  • The manual doesn't state so on p. 10. But if Polaris is not dead center when you go to the home position where the controller reads 0 degrees RA and 0 degrees DEC, I infer that is the time to loosen the clutches and manually put Polaris dead center in RA, DEC, and the attitude knob?

 

Kind Regards,

Koinonos

Umm, you don't want Polaris in the center, you want the celestial pole in the center. Polaris will be off to one side of the pole.



#8 Koinonos

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Posted 27 January 2020 - 01:51 PM

Thank you Glass Eye and Archer1960. 

 

Based on your responses and dealing with the gaps in the manual I think the workflow is.

 

1. Turn on mount that is roughly facing the north celestial pole (if you are in the Northern Hemisphere).

2. Hit Enter twice on the keypad which makes the mount move to its internal markers for RA of 0, and Dec of 0 called the HOME position.  Since the mount has internal index markers, this approach is superior to the CGEM's manual index marker arrow stickers on the mount and is why there are no external index markers on the mount.

3. In the OTA Polaris will not be visible, since the mount is now facing the Celestial Pole which is near, but not on Polaris.

4. Proceed to use the steps on page 8 for rough (mechanical) Polar Alignment by using the adjustment screws for RA and DEC to put Polaris center in the OTA prior to going to page 9 for initial 2 star alignment.

5. Then precise Polar Alignment can proceed as detailed on page 10 of the manual.

 

Where it got muddy for me is that the manual did not state what one should expect to see in the OTA going to the Home position vs. going to Polaris.

 

Kind Regards,

Koinonos 


Edited by Koinonos, 27 January 2020 - 01:53 PM.


#9 archer1960

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Posted 27 January 2020 - 02:57 PM

Thank you Glass Eye and Archer1960. 

 

Based on your responses and dealing with the gaps in the manual I think the workflow is.

 

1. Turn on mount that is roughly facing the north celestial pole (if you are in the Northern Hemisphere).

2. Hit Enter twice on the keypad which makes the mount move to its internal markers for RA of 0, and Dec of 0 called the HOME position.  Since the mount has internal index markers, this approach is superior to the CGEM's manual index marker arrow stickers on the mount and is why there are no external index markers on the mount.

3. In the OTA Polaris will not be visible, since the mount is now facing the Celestial Pole which is near, but not on Polaris.

4. Proceed to use the steps on page 8 for rough (mechanical) Polar Alignment by using the adjustment screws for RA and DEC to put Polaris center in the OTA prior to going to page 9 for initial 2 star alignment.

5. Then precise Polar Alignment can proceed as detailed on page 10 of the manual.

 

Where it got muddy for me is that the manual did not state what one should expect to see in the OTA going to the Home position vs. going to Polaris.

 

Kind Regards,

Koinonos 

Your step 4 isn't really necessary if you are close-enough to be able to find the alignment stars with your finder and then center them in the OTA. I guess it won't hurt, though. At least you'll know pretty precisely the magnitude of your initial misalignment.



#10 SkipW

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Posted 27 January 2020 - 04:12 PM

Thank you Glass Eye and Archer1960. 

 

Based on your responses and dealing with the gaps in the manual I think the workflow is.

 

1. Turn on mount that is roughly facing the north celestial pole (if you are in the Northern Hemisphere).

2. Hit Enter twice on the keypad which makes the mount move to its internal markers for RA of 0, and Dec of 0 called the HOME position.  Since the mount has internal index markers, this approach is superior to the CGEM's manual index marker arrow stickers on the mount and is why there are no external index markers on the mount.

3. In the OTA Polaris will not be visible, since the mount is now facing the Celestial Pole which is near, but not on Polaris.

4. Proceed to use the steps on page 8 for rough (mechanical) Polar Alignment by using the adjustment screws for RA and DEC to put Polaris center in the OTA prior to going to page 9 for initial 2 star alignment.

5. Then precise Polar Alignment can proceed as detailed on page 10 of the manual.

 

Where it got muddy for me is that the manual did not state what one should expect to see in the OTA going to the Home position vs. going to Polaris.

 

Kind Regards,

Koinonos 

When at the home position, the OTA will theoretically be pointed at exactly the same place the polar axis happens to be pointing at the time. There's no way to predict exactly where it's pointing, so the manual has no way of knowing what you will see. If you use the adjustment screws to move the PA so that the optics point at Polaris, that's theoretically where the PA is also pointing. This is close to the pole, but not exactly on it.

 

I say theoretically, because in at that position the optical axis should be exactly parallel with the polar axis, but in reality there will always be some misalignment between the optical axis and the polar axis, because nothing can be manufactured perfectly. Doing a multi-star calibration after the initial 2-star alignment allows the amount and direction of the most common and typically largest of these imperfections to be determined so they can be compensated for.

 

Note that the Polar Align the Mount step on p.8 of the CGX-L manual includes:

If you are not using the optional polar

alignment scope, you can achieve a rough polar alignment
by sighting through the viewfinder of your telescope, and
adjusting the mount until you center Polaris in the eyepiece
of your telescope. This will get you to within about three-quarters
of a degree within the North Celestial Pole
(NCP).

(emphasis added)

 

If you're already reasonably close to polar aligned, as Archer notes, just skip that step. The Celestron alignment procedure is quite tolerant of polar misalignment for the purpose of accurate go-tos, and you will need to do much better than sighting on Polaris through the OTA to get tracking accurate enough for deep-sky astrophotography, anyway. Being more accurately polar aligned will make the first and maybe second alignment star closer to where it stops slewing during the alignment step, but after that PA doesn't matter much, if at all for accurate go-tos. More accurate PA will also make your targets drift in declination more slowly when viewing.




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