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How accurate are the bubble levels in the top of the Losmandy G11 mount?

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15 replies to this topic

#1 Higgsfield

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Posted 04 May 2021 - 04:05 PM

I'm really struggling with this. I leveled off my Losmandy pier adapter in multiple  directions. When I insert and lock down the mount the bubble levels are well off. Why? We are talking a lot off. Should I be working off of the bubbles or the top surface of the adapter?

 

I'm finding that my polar alignment shifts as I slew the mount to various targets. At least that is what I get from PHD2. I was under the impression that strictly speaking the mount did not need to be absolutely level. Have I got this wrong?


Edited by Higgsfield, 04 May 2021 - 04:07 PM.


#2 Dynan

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Posted 04 May 2021 - 04:11 PM

Can't trust the bubble levels. At least I found I couldn't. Celestron and iOptron both fail when compared to a good level. Use a good carpenter's level of proper length on the mount plate. Your PA will thank you, even tough perfect level isn't required, it quickens the process a bunch.


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#3 PFitzhorn

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Posted 04 May 2021 - 04:12 PM

When I got my G11G and installed it, I found the bubble levels weren't to be trusted.  I purchased a Kapro 846 Cyclops on amazon.com and use it each time I set CWD. I've found that this level provides repeatable results for both axes.

 

If your PA is accurate, as has been discussed numerous times in the forums here, leveling the mount is not overly important.


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#4 Christine_Z

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Posted 04 May 2021 - 04:29 PM

If your PA is accurate, as has been discussed numerous times in the forums here, leveling the mount is not overly important.

This cannot be overstated enough


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#5 Wildetelescope

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Posted 04 May 2021 - 04:32 PM

I find them to be fine. But I do not use them to level my pier. The RA axis level moves, so you can never be sure it is orthogonal to the level in the base. I use the RA level and dec level to determine a consistent cw down starting point. I use a carpenter level to level my pier.

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#6 Wildetelescope

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Posted 04 May 2021 - 04:32 PM

I find them to be fine. But I do not use them to level my pier. The RA axis level moves, so you can never be sure it is orthogonal to the level in the base. I use the RA level and dec level to determine a consistent cw down starting point. I use a carpenter level to level my pier.

Jmd

#7 Supernova74

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Posted 04 May 2021 - 04:35 PM

Well considering it’s the sort of thing that can come out of your Xmas cracker um!?about much use as a chocolate kettle unfortunately the best method i find is to use a small builders level and level from axis to axis of the three tripod legs ie one leg to the other then place the mount EQ head on tripod.



#8 Higgsfield

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Posted 04 May 2021 - 05:35 PM

Thank you for your comments. Any thoughts on why my polar alignment seems to shift with mount rotation? I use the polemaster, could it be the setting of the camera and/or adapter possibly?



#9 Dynan

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Posted 04 May 2021 - 06:48 PM

If your alignment shifts with rotation, you aren't polar aligned.

 

I'm on a pier that is well settled in the ground by now...two years plus. I check it each session (once the pier got accidentally hit by a riding mower). I'm overly fussy, but I figure if I'm going to do it, I'm going to get so close that any variance is probably due to seeing.

 

I rotate my mount 90° (6 hours RA) East or West. This puts my counterweight shaft parallel to the ground. I start SharpCap Pro polar align tool. When SCPA says "Rotate the Mount", I simply return to Zero position (iOptron CEM60). I then adjust.

 

Next I rotate RA the opposite direction of the first PA by 90° and run SCPA again. There is invariably a difference as reported by the PA error. That's because, try as I may, my mount isn't perfectly level. So I adjust again.

 

(As I said, I'm overly fussy and adjust until I'm single digit seconds(") both Up and Down, Right and Left.)

 

Then I do it all again. The second run-through is usually very quick, since both sides of pier are very close, but one side affects the other (because of earlier mentioned non-levelity [is that even a word???])

 

After that insanity, I call it good. Others settle for being within minutes, which is fine since guiding will take care of tracking. I just do it this way since it's so infrequent that I need to do it...may as well spend the extra  minutes.

 

When I'm finished, PA doesn't shift in RA or DEC.

 

Without a pier this would be a total waste of time. But back to your original question, I believe your PA if off if you lose star position alignment when you rotate.


Edited by Dynan, 04 May 2021 - 09:53 PM.


#10 Higgsfield

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Posted 04 May 2021 - 09:45 PM

If you alignment shifts with rotation, you aren't polar aligned.

 

I'm on a pier that is well settled in the ground by now...two years plus. I check it each session (once the pier got accidentally hit by a riding mower). I'm overly fussy, but I figure if I'm going to do it, I'm going to get so close that any variance is probably due to seeing.

 

I rotate my mount 90° (6 hours RA) East or West. This puts my counterweight shaft parallel to the ground. I start SharpCap Pro polar align tool. When SCPA says "Rotate the Mount", I simply return to Zero position (iOptron CEM60). I then adjust.

 

Next I rotate RA the opposite direction of the first PA by 90° and run SCPA again. There is invariably a difference as reported by the PA error. That's because, try as I may, my mount isn't perfectly level. So I adjust again.

 

(As I said, I'm overly fussy and adjust until I'm single digit seconds(") both Up and Down, Right and Left.)

 

Then I do it all again. The second run-through is usually very quick, since both sides of pier are very close, but one side affects the other (because of earlier mentioned non-levelity [is that even a word???])

 

After that insanity, I call it good. Others settle for being within minutes, which is fine since guiding will take care of tracking. I just do it this way since it's so infrequent that I need to do it...may as well spend the extra  minutes.

 

When I'm finished, PA doesn't shift in RA or DEC.

 

Without a pier this would be a total waste of time. But back to your original question, I believe your PA if off if you lose star position alignment when you rotate.

Thanks very much for sharing your thoughts on this. It's becoming an obsession for me too. I now polar align every session, but I'm not getting there with the Polemaster it would seem. I will give SharpCap a go.

 

I like your procedure and will give it a try. I am fastidious about it. I presently start it in the CWD position and rotate 30° twice to the right. 

 

Are you saying that the degree of level matters in this process? Could you please say more on this topic.


Edited by Higgsfield, 04 May 2021 - 09:47 PM.


#11 Dynan

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Posted 04 May 2021 - 10:05 PM

Being unlevel will not prevent a good polar alignment. I read a quote from a respected source (that I cannot remember ATM). The gist was..."You can mount an equatorial mount on a wall. If you adjust it correctly, your PA will be perfect."

 

Q: Are you saying that the degree of level matters in this process?

 

The closer you are to 'true level' the less variance you will have from side to side of pier, making final PA easier. But you can PA any mount at any degree of level...if you have enough travel on your adjusters...but there is a limit to practicality, and silliness.


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#12 PFitzhorn

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Posted 05 May 2021 - 10:38 AM

I used a PoleMaster on my Losmandy G11G for several years and did not see the PA error you described, on a tripod or on a pier.  Frankly, if your mount is polar aligned, it's polar aligned.  I would think if you have a good PA (within an arc second or so), using another PA method won't help. A slight (and I mean, slight) shift in the mount during slewing would mess with your PA.

 

So, assuming you're using the PoleMaster correctly (and that's a pretty easy assumption since it's pretty easy to use), some questions I would consider in your situation. Is my mount overloaded? Is it well balanced in both axes? Does the tripod shift a bit during slew (one foot sinking or something)? Are there cables pulling on the scope whose tension rises and falls depending on RA and DEC? Those kind of things.


Edited by PFitzhorn, 05 May 2021 - 11:25 AM.


#13 Higgsfield

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Posted 05 May 2021 - 12:41 PM

I used a PoleMaster on my Losmandy G11G for several years and did not see the PA error you described, on a tripod or on a pier.  Frankly, if your mount is polar aligned, it's polar aligned.  I would think if you have a good PA (within an arc second or so), using another PA method won't help. A slight (and I mean, slight) shift in the mount during slewing would mess with your PA.

 

So, assuming you're using the PoleMaster correctly (and that's a pretty easy assumption since it's pretty easy to use), some questions I would consider in your situation. Is my mount overloaded? Is it well balanced in both axes? Does the tripod shift a bit during slew (one foot sinking or something)? Are there cables pulling on the scope whose tension rises and falls depending on RA and DEC? Those kind of things.

 

Thank you for this list of things to consider.  I'm set up on a concrete pier similar to yours. I will  compare with the SharpCap method. They are very different. Right now I do not seem able to get SharpCap to work with the Polemaster camera. Oh the many joys of astrophotography! Balance is not an issue. I recently had both worms off so was able to exactly determine the points of balance. Certainly not overloaded. I like the platesolving aspect of SharpCap and will report back if I deiscover anything. I'm sure it is non obvious. 



#14 timmbottoni

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Posted 05 May 2021 - 01:19 PM

Being unlevel will not prevent a good polar alignment. I read a quote from a respected source (that I cannot remember ATM). The gist was..."You can mount an equatorial mount on a wall. If you adjust it correctly, your PA will be perfect."

 

Q: Are you saying that the degree of level matters in this process?

 

The closer you are to 'true level' the less variance you will have from side to side of pier, making final PA easier. But you can PA any mount at any degree of level...if you have enough travel on your adjusters...but there is a limit to practicality, and silliness.

Makes total sense if you think about it.  The tripod, pier, or mount being level to start is just a good practice so that when you do your precise PA routine (whatever is used) you are truly only adjusting only AZ or ALT one at a time.  If you aren't level, or reasonably close to it when you start, you might struggle a little, but in the end, once polar aligned, it would have made no difference if your mount/tripod/pier was level when you started.

 

Hope that makes sense.


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#15 chanrobi

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Posted 06 May 2021 - 11:10 AM

Doesn't matter at all if the mount is level or not, period



#16 Sacred Heart

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Posted Yesterday, 08:16 AM

Thank you for this list of things to consider.  I'm set up on a concrete pier similar to yours. I will  compare with the SharpCap method. They are very different. Right now I do not seem able to get SharpCap to work with the Polemaster camera. Oh the many joys of astrophotography! Balance is not an issue. I recently had both worms off so was able to exactly determine the points of balance. Certainly not overloaded. I like the platesolving aspect of SharpCap and will report back if I deiscover anything. I'm sure it is non obvious. 

When you get things up and running,  be patient with Sharpcap polar align.  When making your polar alignment adjustments, wait a few exposures for your numbers to settle down.  Sometimes I will see the numbers get worse and I did not move the mount - my guess is FOV.   Maybe it is my equipment, using a QHY 462 camera with a small refractor, I do admit I need a bigger sensor camera.   I think you should have like a 1.5 - 2.5 degree FOV.  I start with the scope a little past horizontal,  enough to see you are past horizontal, then for the second shot I go to CWD.   I try to get it 10 seconds or under in both Alt and AZ,  then Joey is happy.   A good friend of mine told me about polar alignments,  some days they fall right in your lap - then there are times you could not buy a polar alignment.

 

My experiences,   Joe


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