PEMPro and accurate polar alignment


Hemant Hariyani
 

Hello all,

I set up my ap 1600 in my backyard observatory and have been trying to get a very accurate polar alignment.

I started with RAPAS and only in a couple of minutes, it got me very close. PEMPro showed it to be under 1 arcmin on Azimuth and under 5 arcmin on Altitude!

I then tried to use PEMPro and I am now under 0.5 arcmins on both Azimuth and Altitude. I have seen different runs vary from 0.1 armins to 0.4 arcmins. Is this expected?

I have uploaded snapshots of altitude and azimuth graphs here:


I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec.

How accurate do I need to get with PEMPro for unguided exposures at that focal length with encoders?

Will APCC pro help with unguided exporures?

Regards
Hemant


Roland Christen
 


I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec
You WILL get trailing. Why you ask? Reason is that you did not do a drift alignment in RA by adjusting the altitude axis. I have posted this method of alignment many times on this user group. You can be dead nuts on the pole according to pole align software, but that will not produce zero drift in RA at the zenith. What will produce zero drift in RA at the zenith, you ask? Doing a drift alignment at the zenith by zeroing out drift using the altitude axis adjustment.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.

Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

Rolando


-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto]
To: ap-gto
Sent: Sat, Sep 23, 2017 1:55 pm
Subject: [ap-gto] PEMPro and accurate polar alignment



Hello all,

I set up my ap 1600 in my backyard observatory and have been trying to get a very accurate polar alignment.

I started with RAPAS and only in a couple of minutes, it got me very close. PEMPro showed it to be under 1 arcmin on Azimuth and under 5 arcmin on Altitude!

I then tried to use PEMPro and I am now under 0.5 arcmins on both Azimuth and Altitude. I have seen different runs vary from 0.1 armins to 0.4 arcmins. Is this expected?

I have uploaded snapshots of altitude and azimuth graphs here:


I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec.

How accurate do I need to get with PEMPro for unguided exposu res at that focal length with encoders?

Will APCC pro help with unguided exporures?

Regards
Hemant




Hemant Hariyani
 

Hello Roland,

Thanks a lot. I did not do a drift alignment in RA using altitude axis. I will look up your posts and do this.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.
I do have the encoder mount and do not have PEC on.

>Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the ?>mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

I have a Meade 16 inch ACF f/8 and it was advertised to have zero image shift internal focuser. But I will lock the mirror and try again.

Regards
Hemant
 

On Sat, Sep 23, 2017 at 2:21 PM, chris1011@... [ap-gto] <ap-gto@...> wrote:
 


I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec
You WILL get trailing. Why you ask? Reason is that you did not do a drift alignment in RA by adjusting the altitude axis. I have posted this method of alignment many times on this user group. You can be dead nuts on the pole according to pole align software, but that will not produce zero drift in RA at the zenith. What will produce zero drift in RA at the zenith, you ask? Doing a drift alignment at the zenith by zeroing out drift using the altitude axis adjustment.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.

Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

Rolando


-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto] <ap-gto@...>
To: ap-gto <ap-gto@...>
Sent: Sat, Sep 23, 2017 1:55 pm
Subject: [ap-gto] PEMPro and accurate polar alignment



Hello all,

I set up my ap 1600 in my backyard observatory and have been trying to get a very accurate polar alignment.

I started with RAPAS and only in a couple of minutes, it got me very close. PEMPro showed it to be under 1 arcmin on Azimuth and under 5 arcmin on Altitude!

I then tried to use PEMPro and I am now under 0.5 arcmins on both Azimuth and Altitude. I have seen different runs vary from 0.1 armins to 0.4 arcmins. Is this expected?

I have uploaded snapshots of altitude and azimuth graphs here:


I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec.

How accurate do I need to get with PEMPro for unguided exposu res at that focal length with encoders?

Will APCC pro help with unguided exporures?

Regards
Hemant





Roland Christen
 

At your focal length and aperture you will get oval stars if the tracking in either axis is off by as little as 1 arc second in a 5 minute period. Doing a perfect drift align at the zenith does not guarantee that you will have zero drift as you go away from the zenith. In fact, you can almost guarantee drift elsewhere in the sky just simply due to atmospheric refraction, never mind any misalignments or slight motions in your scope.

If you want no drift over the whole sky you will need to do a pointing/tracking model, and that requires APCC Pro. Others can chime in that have used this program successfully. We have a number of customers with permanent mount installations that do unguided imaging using this program.

Rolando



-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto]
To: ap-gto
Sent: Sat, Sep 23, 2017 2:44 pm
Subject: Re: [ap-gto] PEMPro and accurate polar alignment



Hello Roland,

Thanks a lot. I did not do a drift alignment in RA using altitude axis. I will look up your posts and do this.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.
I do have the encoder mount and do not have PEC on.

>Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the ?>mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

I have a Meade 16 inch ACF f/8 and it was advertised to have zero image shift internal focuser. But I will lock the mirror and try again.

Regards
Hemant
 

On Sat, Sep 23, 2017 at 2:21 PM, chris1011@... [ap-gto] <ap-gto@...> wrote:
 

I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec
You WILL get trailing. Why you ask? Reason is that you did not do a drift alignment in RA by adjusting the altitude axis. I have posted this method of alignment many times on this user group. You can be dead nuts on the pole according to pole align software, but that will not produce zero drift in RA at the zenith. What will produce zero drift in RA at the zenith, you ask? Doing a drift alignment at the zenith by zeroing out drift using the altitude axis adjustment.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.

Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

Rolando


-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto] <ap-gto@...>
To: ap-gto <ap-gto@...>
Sent: Sat, Sep 23, 2017 1:55 pm
Subject: [ap-gto] PEMPro and accurate polar alignment



Hello all,

I set up my ap 1600 in my backyard observatory and have been trying to get a very accurate polar alignment.

I started with RAPAS and only in a couple of minutes, it got me very close. PEMPro showed it to be under 1 arcmin on Azimuth and under 5 arcmin on Altitude!

I then tried to use PEMPro and I am now under 0.5 arcmins on both Azimuth and Altitude. I have seen different runs vary from 0.1 armins to 0.4 arcmins. Is this expected?

I have uploaded snapshots of altitude and azimuth graphs here:


I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec.

How accurate do I need to get with PEMPro for unguided exposu res at that focal length with encoders?

Will APCC pro help with unguided exporures?

Regards
Hemant







Bill Long
 

So, would a 700mm refractor (its actually a 1000mm refractor with a .7x reducer on it) be ideal for running through your PEMPro instructions?




From: ap-gto@... on behalf of chris1011@... [ap-gto]
Sent: Saturday, September 23, 2017 1:38 PM
To: ap-gto@...
Subject: Re: [ap-gto] PEMPro and accurate polar alignment
 
 

At your focal length and aperture you will get oval stars if the tracking in either axis is off by as little as 1 arc second in a 5 minute period. Doing a perfect drift align at the zenith does not guarantee that you will have zero drift as you go away from the zenith. In fact, you can almost guarantee drift elsewhere in the sky just simply due to atmospheric refraction, never mind any misalignments or slight motions in your scope.

If you want no drift over the whole sky you will need to do a pointing/tracking model, and that requires APCC Pro. Others can chime in that have used this program successfully. We have a number of customers with permanent mount installations that do unguided imaging using this program.

Rolando




-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto]
To: ap-gto
Sent: Sat, Sep 23, 2017 2:44 pm
Subject: Re: [ap-gto] PEMPro and accurate polar alignment



Hello Roland,

Thanks a lot. I did not do a drift alignment in RA using altitude axis. I will look up your posts and do this.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.
I do have the encoder mount and do not have PEC on.

>Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the ?>mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

I have a Meade 16 inch ACF f/8 and it was advertised to have zero image shift internal focuser. But I will lock the mirror and try again.

Regards
Hemant
 

On Sat, Sep 23, 2017 at 2:21 PM, chris1011@... [ap-gto] <ap-gto@...> wrote:
 

I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec
You WILL get trailing. Why you ask? Reason is that you did not do a drift alignment in RA by adjusting the altitude axis. I have posted this method of alignment many times on this user group. You can be dead nuts on the pole according to pole align software, but that will not produce zero drift in RA at the zenith. What will produce zero drift in RA at the zenith, you ask? Doing a drift alignment at the zenith by zeroing out drift using the altitude axis adjustment.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.

Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

Rolando


-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto] <ap-gto@...>
To: ap-gto <ap-gto@...>
Sent: Sat, Sep 23, 2017 1:55 pm
Subject: [ap-gto] PEMPro and accurate polar alignment



Hello all,

I set up my ap 1600 in my backyard observatory and have been trying to get a very accurate polar alignment.

I started with RAPAS and only in a couple of minutes, it got me very close. PEMPro showed it to be under 1 arcmin on Azimuth and under 5 arcmin on Altitude!

I then tried to use PEMPro and I am now under 0.5 arcmins on both Azimuth and Altitude. I have seen different runs vary from 0.1 armins to 0.4 arcmins. Is this expected?

I have uploaded snapshots of altitude and azimuth graphs here:


I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec.

How accurate do I need to get with PEMPro for unguided exposu res at that focal length with encoders?

Will APCC pro help with unguided exporures?

Regards
Hemant







Roland Christen
 

Sure. Try it.

Rolando



-----Original Message-----
From: Bill Long bill@... [ap-gto]
To: ap-gto
Sent: Sat, Sep 23, 2017 3:41 pm
Subject: Re: [ap-gto] PEMPro and accurate polar alignment



So, would a 700mm refractor (its actually a 1000mm refractor with a .7x reducer on it) be ideal for running through your PEMPro instructions?



From: ap-gto@... gto@...> on behalf of chris1011@... [ap-gto] gto@...>
Sent: Saturday, September 23, 2017 1:38 PM
To: ap-gto@...
Subject: Re: [ap-gto] PEMPro and accurate polar alignment
 
 
At your focal length and aperture you will get oval stars if the tracking in either axis is off by as little as 1 arc second in a 5 minute period. Doing a perfect drift align at the zenith does not guarantee that you will have zero drift as you go away from the zenith. In fact, you can almost guarantee drift elsewhere in the sky just simply due to atmospheric refraction, never mind any misalignments or slight motions in your scope.

If you want no drift over the whole sky you will need to do a pointing/tracking model, and that requires APCC Pro. Others can chime in that have used this program successfully. We have a number of customers with permanent mount installations that do unguided imaging using this program.

Rolando



-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto] gto@...>
To: ap-gto gto@...>
Sent: Sat, Sep 23, 2017 2:44 pm
Subject: Re: [ap-gto] PEMPro and accurate polar alignment



Hello Roland,

Thanks a lot. I did not do a drift alignment in RA using altitude axis. I will look up your posts and do this.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.
I do have the encoder mount and do not have PEC on.

>Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the ?>mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

I have a Meade 16 inch ACF f/8 and it was advertised to have zero image shift internal focuser. But I will lock the mirror and try again.

Regards
Hemant
 

On Sat, Sep 23, 2017 at 2:21 PM, chris1011@... [ap-gto] <ap-gto@...> wrote:
 

I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec
You WILL get trailing. Why you ask? Reason is that you did not do a drift alignment in RA by adjusting the altitude axis. I have posted this method of alignment many times on this user group. You can be dead nuts on the pole according to pole align software, but that will not produce zero drift in RA at the zenith. What will produce zero drift in RA at the zenith, you ask? Doing a drift alignment at the zenith by zeroing out drift using the altitude axis adjustment.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.

Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

Rolando


-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto] <ap-gto@...>
To: ap-gto <ap-gto@...>
Sent: Sat, Sep 23, 2017 1:55 pm
Subject: [ap-gto] PEMPro and accurate polar alignment



Hello all,

I set up my ap 1600 in my backyard observatory and have been trying to get a very accurate polar alignment.

I started with RAPAS and only in a couple of minutes, it got me very close. PEMPro showed it to be under 1 arcmin on Azimuth and under 5 arcmin on Altitude!

I then tried to use PEMPro and I am now under 0.5 arcmins on both Azimuth and Altitude. I have seen different runs vary from 0.1 armins to 0.4 arcmins. Is this expected?

I have uploaded snapshots of altitude and azimuth graphs here:


I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec.

How accurate do I need to get with PEMPro for unguided exposu res at that focal length with encoders?

Will APCC pro help with unguided exporures?

Regards
Hemant









cford81@...
 

With my (permanently mounted) absolute encoder AP1600GTO and AP180 F/7 using PemPro and APCC Pro I can now get up to 10 to 15 minutes unguided before stars start going noticeably oval. I suspect I may be able to do even better with an altitude drift align at the zenith as Roland suggests. (PemPro does not default to that position in its standard polar alignment routine) I have also been doing 200+ point maps with APCC Pro which might be more than I need.

I have tried imaging unguided with a 14.5" AGO F/6.7 Dall-Kirkham on the same mount but am having problems going much beyond 5 minutes due to its greater mechanical variability. The rigidity of the AP180 F/7 and AP1600GTO encoder mount combination seems another reason why a big unobstructed refractor is such an ideal imaging instrument. (I have that scope clamped *really* tight in its rings) I just can't beat its precision and sharpness with any other telescope design I have tried unguided imaging with. (And that includes an AP RH305 with an almost identical focal length)

Chris



From: "chris1011@... [ap-gto]"
To: ap-gto@...
Sent: Saturday, September 23, 2017 1:38:27 PM
Subject: Re: [ap-gto] PEMPro and accurate polar alignment

 

At your focal length and aperture you will get oval stars if the tracking in either axis is off by as little as 1 arc second in a 5 minute period. Doing a perfect drift align at the zenith does not guarantee that you will have zero drift as you go away from the zenith. In fact, you can almost guarantee drift elsewhere in the sky just simply due to atmospheric refraction, never mind any misalignments or slight motions in your scope.

If you want no drift over the whole sky you will need to do a pointing/tracking model, and that requires APCC Pro. Others can chime in that have used this program successfully. We have a number of customers with permanent mount installations that do unguided imaging using this program.

Rolando




-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto]
To: ap-gto
Sent: Sat, Sep 23, 2017 2:44 pm
Subject: Re: [ap-gto] PEMPro and accurate polar alignment



Hello Roland,

Thanks a lot. I did not do a drift alignment in RA using altitude axis. I will look up your posts and do this.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.
I do have the encoder mount and do not have PEC on.

>Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the ?>mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

I have a Meade 16 inch ACF f/8 and it was advertised to have zero image shift internal focuser. But I will lock the mirror and try again.

Regards
Hemant
 

On Sat, Sep 23, 2017 at 2:21 PM, chris1011@... [ap-gto] <ap-gto@...> wrote:
 


I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec
You WILL get trailing. Why you ask? Reason is that you did not do a drift alignment in RA by adjusting the altitude axis. I have posted this method of alignment many times on this user group. You can be dead nuts on the pole according to pole align software, but that will not produce zero drift in RA at the zenith. What will produce zero drift in RA at the zenith, you ask? Doing a drift alignment at the zenith by zeroing out drift using the altitude axis adjustment.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.

Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

Rolando


-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto] <ap-gto@...>
To: ap-gto <ap-gto@...>
Sent: Sat, Sep 23, 2017 1:55 pm
Subject: [ap-gto] PEMPro and accurate polar alignment



Hello all,

I set up my ap 1600 in my backyard observatory and have been trying to get a very accurate polar alignment.

I started with RAPAS and only in a couple of minutes, it got me very close. PEMPro showed it to be under 1 arcmin on Azimuth and under 5 arcmin on Altitude!

I then tried to use PEMPro and I am now under 0.5 arcmins on both Azimuth and Altitude. I have seen different runs vary from 0.1 armins to 0.4 arcmins. Is this expected?

I have uploaded snapshots of altitude and azimuth graphs here:


I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec.

How accurate do I need to get with PEMPro for unguided exposu res at that focal length with encoders?

Will APCC pro help with unguided exporures?

Regards
Hemant













Roland Christen
 

Thanks for your post, Chris.

Rolando



-----Original Message-----
From: cford81@... [ap-gto]
To: ap-gto
Sent: Sat, Sep 23, 2017 6:39 pm
Subject: Re: [ap-gto] PEMPro and accurate polar alignment



With my (permanently mounted) absolute encoder AP1600GTO and AP180 F/7 using PemPro and APCC Pro I can now get up to 10 to 15 minutes unguided before stars start going noticeably oval. I suspect I may be able to do even better with an altitude drift align at the zenith as Roland suggests. (PemPro does not default to that position in its standard polar alignment routine) I have also been doing 200+ point maps with APCC Pro which might be more than I need.

I have tried imaging unguided with a 14.5" AGO F/6.7 D all-Kirkham on the same mount but am having problems going much beyond 5 minutes due to its greater mechanical variability. The rigidity of the AP180 F/7 and AP1600GTO encoder mount combination seems another reason why a big unobstructed refractor is such an ideal imaging instrument. (I have that scope clamped *really* tight in its rings) I just can't beat its precision and sharpness with any other telescope design I have tried unguided imaging with. (And that includes an AP RH305 with an almost identical focal length)

Chris



From: "chris1011@... [ap-gto]" gto@...>
To: ap-gto@...
Sent: Saturday, September 23, 2017 1:38:27 PM
Subject: Re: [ap-gto] PEMPro and accurate polar alignment

 
At your focal length and aperture you will get oval stars if the tracking in either axis is off by as little as 1 arc second in a 5 minut e period. Doing a perfect drift align at the zenith does not guarantee that you will have zero drift as you go away from the zenith. In fact, you can almost guarantee drift elsewhere in the sky just simply due to atmospheric refraction, never mind any misalignments or slight motions in your scope.

If you want no drift over the whole sky you will need to do a pointing/tracking model, and that requires APCC Pro. Others can chime in that have used this program successfully. We have a number of customers with permanent mount installations that do unguided imaging using this program.

Rolando



-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto] gto@...>
To: ap-gto gto@...>
Sent: Sat, Sep 23, 2017 2:44 pm
Subject: Re: [ap-gto] PEMPro and accurate polar alignment



Hello Roland,

Thanks a lot. I did not do a drift alignment in RA using altitude axis. I will look up your posts and do this.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.
I do have t he encoder mount and do not have PEC on.

>Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the ?>mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

I have a Meade 16 inch ACF f/8 and it was advertised to have zero image shift internal focuser. But I will lock the mirror and try again.

Regards
Hemant
 

On Sat, Sep 23, 2017 at 2:21 PM, chris1011@... [ap-gto] <ap-g to@...> wrote:
 


I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec
You WILL get trailing. Why you ask? Reason is that you did not do a drift alignment in RA by adjusting the altitude axis. I have posted this method of alignment many times on this user group. You can be dead nuts on the pole according to pole align software, but that will not produce zero drift in RA at the zenith. What will produce zero drift in RA at the zenith, you ask? Doing a drift alignment at the zenith by zeroing out drift using the altitude axis adjustment.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.

Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

Rolando


-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto] <ap-gto@...>
To: ap-gto <ap-gto@...>
Sent: Sat, Sep 23, 2017 1:55 pm
Subject: [ap-gto] PEMPro and accurate polar alignment



Hell o all,

I set up my ap 1600 in my backyard observatory and have been trying to get a very accurate polar alignment.

I started with RAPAS and only in a couple of minutes, it got me very close. PEMPro showed it to be under 1 arcmin on Azimuth and under 5 arcmin on Altitude!

I then tried to use PEMPro and I am now under 0.5 arcmins on both Azimuth and Altitude. I have seen different runs vary from 0.1 armins to 0.4 arcmins. Is this expected?

I have uploaded snapshots of altitude and azimuth graphs here:


I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec.

How accurate do I need to get with PEMPro for unguided exposu res at that focal length with encoders?

Will APCC pro help with unguided exporures?

Regards
Hemant















CurtisC
 

"I did not do a drift alignment in RA using altitude axis. I will look up your posts and do this."

Somehow I've missed these posts.


CurtisC
 

"I did not do a drift alignment in RA using altitude axis. I will look up your posts and do this."

Somehow I've missed these posts.


steven ho
 

I too have been wondering why after painstaking drift alignment some stars were out of round. When the student is ready the teacher appears. How true indeed!! Thanks Roland and others for your support. 


steve hoffman



From: ap-gto@... on behalf of chris1011@... [ap-gto]
Sent: Saturday, September 23, 2017 3:21 PM
To: ap-gto@...
Subject: Re: [ap-gto] PEMPro and accurate polar alignment
 
 


I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec
You WILL get trailing. Why you ask? Reason is that you did not do a drift alignment in RA by adjusting the altitude axis. I have posted this method of alignment many times on this user group. You can be dead nuts on the pole according to pole align software, but that will not produce zero drift in RA at the zenith. What will produce zero drift in RA at the zenith, you ask? Doing a drift alignment at the zenith by zeroing out drift using the altitude axis adjustment.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.

Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

Rolando


-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto]
To: ap-gto
Sent: Sat, Sep 23, 2017 1:55 pm
Subject: [ap-gto] PEMPro and accurate polar alignment



Hello all,

I set up my ap 1600 in my backyard observatory and have been trying to get a very accurate polar alignment.

I started with RAPAS and only in a couple of minutes, it got me very close. PEMPro showed it to be under 1 arcmin on Azimuth and under 5 arcmin on Altitude!

I then tried to use PEMPro and I am now under 0.5 arcmins on both Azimuth and Altitude. I have seen different runs vary from 0.1 armins to 0.4 arcmins. Is this expected?

I have uploaded snapshots of altitude and azimuth graphs here:


I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec.

How accurate do I need to get with PEMPro for unguided exposu res at that focal length with encoders?

Will APCC pro help with unguided exporures?

Regards
Hemant




Hemant Hariyani
 

Roland,

Thanks a lot again. This is really very helpful. I do intend to start using APCC Pro soon and create a pointing/tracking model.

Regards
Hemant


On Sat, Sep 23, 2017 at 3:38 PM, chris1011@... [ap-gto] <ap-gto@...> wrote:
 

At your focal length and aperture you will get oval stars if the tracking in either axis is off by as little as 1 arc second in a 5 minute period. Doing a perfect drift align at the zenith does not guarantee that you will have zero drift as you go away from the zenith. In fact, you can almost guarantee drift elsewhere in the sky just simply due to atmospheric refraction, never mind any misalignments or slight motions in your scope.

If you want no drift over the whole sky you will need to do a pointing/tracking model, and that requires APCC Pro. Others can chime in that have used this program successfully. We have a number of customers with permanent mount installations that do unguided imaging using this program.

Rolando




-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto] <ap-gto@...>
To: ap-gto <ap-gto@...>
Sent: Sat, Sep 23, 2017 2:44 pm
Subject: Re: [ap-gto] PEMPro and accurate polar alignment



Hello Roland,

Thanks a lot. I did not do a drift alignment in RA using altitude axis. I will look up your posts and do this.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.
I do have the encoder mount and do not have PEC on.

>Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the ?>mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

I have a Meade 16 inch ACF f/8 and it was advertised to have zero image shift internal focuser. But I will lock the mirror and try again.

Regards
Hemant
 

On Sat, Sep 23, 2017 at 2:21 PM, chris1011@... [ap-gto] <ap-gto@...> wrote:
 

I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec
You WILL get trailing. Why you ask? Reason is that you did not do a drift alignment in RA by adjusting the altitude axis. I have posted this method of alignment many times on this user group. You can be dead nuts on the pole according to pole align software, but that will not produce zero drift in RA at the zenith. What will produce zero drift in RA at the zenith, you ask? Doing a drift alignment at the zenith by zeroing out drift using the altitude axis adjustment.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.

Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

Rolando


-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto] <ap-gto@...>
To: ap-gto <ap-gto@...>
Sent: Sat, Sep 23, 2017 1:55 pm
Subject: [ap-gto] PEMPro and accurate polar alignment



Hello all,

I set up my ap 1600 in my backyard observatory and have been trying to get a very accurate polar alignment.

I started with RAPAS and only in a couple of minutes, it got me very close. PEMPro showed it to be under 1 arcmin on Azimuth and under 5 arcmin on Altitude!

I then tried to use PEMPro and I am now under 0.5 arcmins on both Azimuth and Altitude. I have seen different runs vary from 0.1 armins to 0.4 arcmins. Is this expected?

I have uploaded snapshots of altitude and azimuth graphs here:


I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec.

How accurate do I need to get with PEMPro for unguided exposu res at that focal length with encoders?

Will APCC pro help with unguided exporures?

Regards
Hemant








Hemant Hariyani
 

Chris,

Thanks so much for sharing your experience. This is very helpful and I will certainly keep that in mind.

Regards
Hemant


On Sat, Sep 23, 2017 at 6:39 PM, cford81@... [ap-gto] <ap-gto@...> wrote:
 

With my (permanently mounted) absolute encoder AP1600GTO and AP180 F/7 using PemPro and APCC Pro I can now get up to 10 to 15 minutes unguided before stars start going noticeably oval. I suspect I may be able to do even better with an altitude drift align at the zenith as Roland suggests. (PemPro does not default to that position in its standard polar alignment routine) I have also been doing 200+ point maps with APCC Pro which might be more than I need.

I have tried imaging unguided with a 14.5" AGO F/6.7 Dall-Kirkham on the same mount but am having problems going much beyond 5 minutes due to its greater mechanical variability. The rigidity of the AP180 F/7 and AP1600GTO encoder mount combination seems another reason why a big unobstructed refractor is such an ideal imaging instrument. (I have that scope clamped *really* tight in its rings) I just can't beat its precision and sharpness with any other telescope design I have tried unguided imaging with. (And that includes an AP RH305 with an almost identical focal length)

Chris



From: "chris1011@... [ap-gto]" <ap-gto@...>
To: ap-gto@...
Sent: Saturday, September 23, 2017 1:38:27 PM

Subject: Re: [ap-gto] PEMPro and accurate polar alignment

 

At your focal length and aperture you will get oval stars if the tracking in either axis is off by as little as 1 arc second in a 5 minute period. Doing a perfect drift align at the zenith does not guarantee that you will have zero drift as you go away from the zenith. In fact, you can almost guarantee drift elsewhere in the sky just simply due to atmospheric refraction, never mind any misalignments or slight motions in your scope.

If you want no drift over the whole sky you will need to do a pointing/tracking model, and that requires APCC Pro. Others can chime in that have used this program successfully. We have a number of customers with permanent mount installations that do unguided imaging using this program.

Rolando




-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto] <ap-gto@...>
To: ap-gto <ap-gto@...>
Sent: Sat, Sep 23, 2017 2:44 pm
Subject: Re: [ap-gto] PEMPro and accurate polar alignment



Hello Roland,

Thanks a lot. I did not do a drift alignment in RA using altitude axis. I will look up your posts and do this.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.
I do have the encoder mount and do not have PEC on.

>Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the ?>mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

I have a Meade 16 inch ACF f/8 and it was advertised to have zero image shift internal focuser. But I will lock the mirror and try again.

Regards
Hemant
 

On Sat, Sep 23, 2017 at 2:21 PM, chris1011@... [ap-gto] <ap-gto@...> wrote:
 


I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec
You WILL get trailing. Why you ask? Reason is that you did not do a drift alignment in RA by adjusting the altitude axis. I have posted this method of alignment many times on this user group. You can be dead nuts on the pole according to pole align software, but that will not produce zero drift in RA at the zenith. What will produce zero drift in RA at the zenith, you ask? Doing a drift alignment at the zenith by zeroing out drift using the altitude axis adjustment.

Second thing that will produce trailing is if you have not turned on the PEM compensation, unless of course you have an encoder mount, in which case you need to turn them on.

Third thing that can produce trailing in your image is the stability of your scope. You aren't by any chance trying to get unguided images with a Cassegrain type scope where the mirrors are perhaps slightly loose and could be shifting or tilting, or the focuser is not fully tight without any flex whatsoever?

Rolando


-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto] <ap-gto@...>
To: ap-gto <ap-gto@...>
Sent: Sat, Sep 23, 2017 1:55 pm
Subject: [ap-gto] PEMPro and accurate polar alignment



Hello all,

I set up my ap 1600 in my backyard observatory and have been trying to get a very accurate polar alignment.

I started with RAPAS and only in a couple of minutes, it got me very close. PEMPro showed it to be under 1 arcmin on Azimuth and under 5 arcmin on Altitude!

I then tried to use PEMPro and I am now under 0.5 arcmins on both Azimuth and Altitude. I have seen different runs vary from 0.1 armins to 0.4 arcmins. Is this expected?

I have uploaded snapshots of altitude and azimuth graphs here:


I tried an unguided exposure of 5 mins on M13 and it had trailing at 3200 mm. I will check if it was RA or dec.

How accurate do I need to get with PEMPro for unguided exposu res at that focal length with encoders?

Will APCC pro help with unguided exporures?

Regards
Hemant














Hemant Hariyani
 

Somehow I've missed these posts.

I searched "drift alignment zenith" on ap-gto yahoo groups page and I do see a lot of threads discussing this.

Regards
Hemant


On Sat, Sep 23, 2017 at 10:42 PM, calypte@... [ap-gto] <ap-gto@...> wrote:
 

"I did not do a drift alignment in RA using altitude axis. I will look up your posts and do this."


Somehow I've missed these posts.



CurtisC
 

Then what is the value of PEMPro, if it can't get this right?


Ray Gralak
 

Then what is the value of PEMPro, if it can't get this right?
PEMPro tries to align to the non-refracted pole to minimize field rotation over the night.

Roland's technique of minimizing RA drift is great for short-term unguided tracking in a local area of the sky. The technique eliminates RA drift caused by polar alignment error, refraction, telescope component flexure, and worm wheel eccentricity, all of which can cause slight variations in RA speed.

But, I do not think polar alignment using RA is likely going to be as accurate as using the (non-moving) Declination axis unless there is an encoder on the RA axis to compensate for the worm wheel's (very slight) eccentricity, possible tooth-tooth variations in the worm wheel teeth, and residual periodic error.

Roland, please correct me if I am overlooking something here?

Best regards,

-Ray Gralak
Author of APCC (Astro-Physics Command Center): http://www.astro-physics.com/index.htm?products/accessories/software/apcc/apcc
Author of PEMPro: http://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: http://www.gralak.com/apdriver
Author of PulseGuide: http://www.pulseguide.com
Author of Sigma: http://www.gralak.com/sigma


-----Original Message-----
From: ap-gto@yahoogroups.com [mailto:ap-gto@yahoogroups.com]
Sent: Sunday, September 24, 2017 8:14 AM
To: ap-gto@yahoogroups.com
Subject: Re: [ap-gto] Re: PEMPro and accurate polar alignment



Then what is the value of PEMPro, if it can't get this right?


Hemant Hariyani
 

Then what is the value of PEMPro, if it can't get this right?

I believe PEMPro is probably one of the best utilities when it comes to accurately measuring drift and translating it to alt/az errors in polar alignment and providing a very convenient way to correcting those.

If I am correct, there is no reason why the zenith RA drift alignment cannot be done in PEMPro. May be someone who has done it can correct, but I believe, it is just a matter of changing default declination (to your latitude?) and degrees from meridian (to very close to zero) when calculating altitude error. I will try this out. May be someone experienced can comment.

Regards
Hemant

On Sun, Sep 24, 2017 at 10:14 AM, calypte@... [ap-gto] <ap-gto@...> wrote:
 

Then what is the value of PEMPro, if it can't get this right?



Roland Christen
 


PEMPro tries to align to the non-refracted pole to minimize field rotation over the night.

Roland's technique of minimizing RA drift is great for short-term unguided tracking in a local area of the sky. The technique eliminates RA drift caused by polar alignment error, refraction, telescope component flexure, and worm wheel eccentricity, all of which can cause slight variations in RA speed.

But, I do not think polar alignment using RA is likely going to be as accurate as using the (non-moving) Declination axis unless there is an encoder on the RA axis to compensate for the worm wheel's (very slight) eccentricity, possible tooth-tooth variations in the worm wheel teeth, and residual periodic error.

Roland, please correct me if I am overlooking something here?
Yes Ray, you are absolutely correct. The issue is whether you want zero drift around the zenith, which is useful for unguided imaging, or you want zero Dec drift (and variable RA drift) over larger parts of the sky. You can achieve one or the other. Pointing will be more accurate with the PEMPro drift alignment method, but you will get more RA drift overhead.

Rolando


-----Original Message-----
From: 'Ray Gralak (Groups)' groups3@... [ap-gto]
To: ap-gto
Sent: Sun, Sep 24, 2017 11:26 am
Subject: RE: [ap-gto] Re: PEMPro and accurate polar alignment

> Then what is the value of PEMPro, if it can't get this right?

PEMPro tries to align to the non-refracted pole to minimize field rotation over the night.

Roland's technique of minimizing RA drift is great for short-term unguided tracking in a local area of the sky. The technique eliminates RA drift caused by polar alignment error, refraction, telescope component flexure, and worm wheel eccentricity, all of which can cause slight variations in RA speed.

But, I do not think polar alignment using RA is likely going to be as accurate as using the (non-moving) Declination axis unless there is an encoder on the RA axis to compensate for the worm wheel's (very slight) eccentricity, possible tooth-tooth variations in the worm wheel teeth, and residual periodic error.

Roland, please correct me if I am overlooking something here?

Best regards,

-Ray Gralak
Author of APCC (Astro-Physics Command Center): http://www.astro-physics.com/index.htm?products/accessories/software/apcc/apcc
Author of PEMPro: http://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: http://www.gralak.com/apdriver
Author of PulseGuide: http://www.pulseguide.com
Author of Sigma: http://www.gralak.com/sigma


> -----Original Message-----
> From: ap-gto@... [mailto:ap-gto@...]
> Sent: Sunday, September 24, 2017 8:14 AM
> To: ap-gto@...
> Subject: Re: [ap-gto] Re: PEMPro and accurate polar alignment
>
>
>
> Then what is the value of PEMPro, if it can't get this right?
>
>



------------------------------------
Posted by: "Ray Gralak \(Groups\)" <groups3@...>
------------------------------------

To UNSUBSCRIBE, or for general information on the ap-gto list
see http://groups.yahoo.com/group/ap-gto
------------------------------------

Yahoo Groups Links

<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/ap-gto/

<*> Your email settings:
Individual Email | Traditional

<*> To change settings online go to:
http://groups.yahoo.com/group/ap-gto/join
(Yahoo! ID required)

<*> To change settings via email:
ap-gto-digest@...
ap-gto-fullfeatured@...

<*> To unsubscribe from this group, send an email to:
ap-gto-unsubscribe@...

<*> Your use of Yahoo Groups is subject to:
https://info.yahoo.com/legal/us/yahoo/utos/terms/


Hemant Hariyani
 

I tried measuring drift using PEMPro at zenith and am a bit surprised by the result.

I first tried to change position of altitude drift measurement in PEMPro slew dialogue but I was not able to select a degree offset less than 30. So I slewed my mount to zenith using my latitude as declination and a close to zero degree offset from meridian. I chose to be on the west of meridian.

I then started measurements in PEMPro to start with, it showed a huge offset and asked me to lower my altitude by 60 odd arc minutes. This reduced over a period of time and by the end of 5 minutes run, it was around 15 arc minutes. Without re-positioning the mount to zenith I let it continue for more time, restarting measurements and after about 20 minutes, this was down to 2.8 arc minutes. I tried this again and the results were fairly consistent. I have no idea on what is going on here. I did not affect this significant a change in measurements in such a short period of time. Any guesses on what can be going on? I have encoders enabled.

Regards
Hemant

 

On Mon, Sep 25, 2017 at 10:01 AM, chris1011@... [ap-gto] <ap-gto@...> wrote:
 


PEMPro tries to align to the non-refracted pole to minimize field rotation over the night.

Roland's technique of minimizing RA drift is great for short-term unguided tracking in a local area of the sky. The technique eliminates RA drift caused by polar alignment error, refraction, telescope component flexure, and worm wheel eccentricity, all of which can cause slight variations in RA speed.

But, I do not think polar alignment using RA is likely going to be as accurate as using the (non-moving) Declination axis unless there is an encoder on the RA axis to compensate for the worm wheel's (very slight) eccentricity, possible tooth-tooth variations in the worm wheel teeth, and residual periodic error.

Roland, please correct me if I am overlooking something here?
Yes Ray, you are absolutely correct. The issue is whether you want zero drift around the zenith, which is useful for unguided imaging, or you want zero Dec drift (and variable RA drift) over larger parts of the sky. You can achieve one or the other. Pointing will be more accurate with the PEMPro drift alignment method, but you will get more RA drift overhead.

Rolando


-----Original Message-----
From: 'Ray Gralak (Groups)' groups3@... [ap-gto] <ap-gto@...>
To: ap-gto <ap-gto@...>
Sent: Sun, Sep 24, 2017 11:26 am
Subject: RE: [ap-gto] Re: PEMPro and accurate polar alignment

> Then what is the value of PEMPro, if it can't get this right?

PEMPro tries to align to the non-refracted pole to minimize field rotation over the night.

Roland's technique of minimizing RA drift is great for short-term unguided tracking in a local area of the sky. The technique eliminates RA drift caused by polar alignment error, refraction, telescope component flexure, and worm wheel eccentricity, all of which can cause slight variations in RA speed.

But, I do not think polar alignment using RA is likely going to be as accurate as using the (non-moving) Declination axis unless there is an encoder on the RA axis to compensate for the worm wheel's (very slight) eccentricity, possible tooth-tooth variations in the worm wheel teeth, and residual periodic error.

Roland, please correct me if I am overlooking something here?

Best regards,

-Ray Gralak
Author of APCC (Astro-Physics Command Center): http://www.astro-physics.com/index.htm?products/accessories/software/apcc/apcc
Author of PEMPro: http://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: http://www.gralak.com/apdriver
Author of PulseGuide: http://www.pulseguide.com
Author of Sigma: http://www.gralak.com/sigma


> -----Original Message-----
> From: ap-gto@... [mailto:ap-gto@...]
> Sent: Sunday, September 24, 2017 8:14 AM
> To: ap-gto@...
> Subject: Re: [ap-gto] Re: PEMPro and accurate polar alignment
>
>
>
> Then what is the value of PEMPro, if it can't get this right?
>
>



------------------------------------
Posted by: "Ray Gralak \(Groups\)" <groups3@...>
------------------------------------

To UNSUBSCRIBE, or for general information on the ap-gto list
see http://groups.yahoo.com/group/ap-gto
------------------------------------

Yahoo Groups Links

<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/ap-gto/

<*> Your email settings:
Individual Email | Traditional

<*> To change settings online go to:
http://groups.yahoo.com/group/ap-gto/join
(Yahoo! ID required)

<*> To change settings via email:
ap-gto-digest@...
ap-gto-fullfeatured@yahoogroups.com

<*> To unsubscribe from this group, send an email to:
ap-gto-unsubscribe@yahoogroups.com

<*> Your use of Yahoo Groups is subject to:
https://info.yahoo.com/legal/us/yahoo/utos/terms/



Roland Christen
 

Here's what I do at the zenith. I link to the mount via MaximDL, acquire a guide star and start a guide exposure with aggressiveness set to zero. I open the tracking Error Graph and watch the RA drift. After a few minutes it is apparent that the drift is either + or -. In my case I know that with my camera orientation a minus drift means I need to raise the altitude axis, but in your case you need to make that determination by trial and error.

How much to lower or raise? Usually from a PEMPro drift method to the zenith adjustment the difference is about 1/4 rotation of the altitude adjustment wheel. In my case, after this adjustment I get less than 1 arc sec drift in a 15 minute time period on either side of the zenith up to about +-1 hour. Beyond those boundaries that, the drift begins to increase, but even though there is slightly more drift I can still do 5 to 10 minutes with no ovality showing up in the stars.

For those wishing to wade thru more rigorous methods of polar alignment and a handy calculator, here are two websites:
http://canburytech.net/DriftAlign/DriftAlign_3.html
http://www.bbastrodesigns.com/equatTrackingRatesCalc.html

Rolando



-----Original Message-----
From: Hemant Hariyani hemanthariyani@... [ap-gto]
To: ap-gto
Sent: Mon, Sep 25, 2017 12:54 pm
Subject: Re: [ap-gto] Re: PEMPro and accurate polar alignment



I tried measuring drift using PEMPro at zenith and am a bit surprised by the result.

I first tried to change position of altitude drift measurement in PEMPro slew dialogue but I was not able to select a degree offset less than 30. So I slewed my mount to zenith using my latitude as declination and a close to zero degree offset from meridian. I chose to be on the west of meridian.

I then started measurements in PEMPro to start with, it showed a huge offset and asked me to lower my altitude by 60 odd arc minutes. This reduced over a period of time and by the end of 5 minutes run, it was around 15 arc minutes. Without re-positioning the mount to zenith I let it continue for more time, restarting measurements and after about 20 minutes, this was down to 2.8 arc minutes. I tried this again and the results were fairly consistent. I have no idea on what is going on here. I did not affect this significant a change in measurements in such a short period of time. Any guesses on what can be going on? I have encoders enabled.

Regards
Hemant

 

On Mon, Sep 25, 2017 at 10:01 AM, chris1011@... [ap-gto] <ap-gto@...> wrote:
 

PEMPro tries to align to the non-refracted pole to minimize field rotation over the night.

Roland's technique of minimizing RA drift is great for short-term unguided tracking in a local area of the sky. The technique eliminates RA drift caused by polar alignment error, refraction, telescope component flexure, and worm wheel eccentricity, all of which can cause slight variations in RA speed.

But, I do not think polar alignment using RA is likely going to be as accurate as using the (non-moving) Declination axis unless there is an encoder on the RA axis to compensate for the worm wheel's (very slight) eccentricity, possible tooth-tooth variations in the worm wheel teeth, and residual periodic error.

Roland, please correct me if I am overlooking something here?
Yes Ray, you are absolutely correct. The issue is whether you want zero drift around the zenith, which is useful for unguided imaging, or you want zero Dec drift (and variable RA drift) over larger parts of the sky. You can achieve one or the other. Pointing will be more accurate with the PEMPro drift alignment method, but you will get more RA drift overhead.

Rolando


-----Original Message-----
From: 'Ray Gralak (Groups)' groups3@... [ap-gto] <ap-gto@...>
To: ap-gto <ap-gto@...>
Sent: Sun, Sep 24, 2017 11:26 am
Subject: RE: [ap-gto] Re: PEMPro and accurate polar alignment

> Then what is the value of PEMPro, if it can't get this right?

PEMPro tries to align to the non-refracted pole to minimize field rotation over the night.

Roland's technique of minimizing RA drift is great for short-term unguided tracking in a local area of the sky. The technique eliminates RA drift caused by polar alignment error, refraction, telescope component flexure, and worm wheel eccentricity, all of which can cause slight variations in RA speed.

But, I do not think polar alignment using RA is likely going to be as accurate as using the (non-moving) Declination axis unless there is an encoder on the RA axis to compensate for the worm wheel's (very slight) eccentricity, possible tooth-tooth variations in the worm wheel teeth, and residual periodic error.

Roland, please correct me if I am overlooking something here?

Best regards,

-Ray Gralak
Author of APCC (Astro-Physics Command Center): http://www.astro-physics.com/index.htm?products/accessories/software/apcc/apcc
Author of PEMPro: http://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: http://www.gralak.com/apdriver
Author of PulseGuide: http://www.pulseguide.com
Author of Sigma: http://www.gralak.com/sigma


> -----Original Message-----
> From: ap-gto@... [mailto:ap-gto@...]
> Sent: Sunday, September 24, 2017 8:14 AM
> To: ap-gto@...
> Subject: Re: [ap-gto] Re: PEMPro and accurate polar alignment
>
>
>
> Then what is the value of PEMPro, if it can't get this right?
>
>



------------------------------------
Posted by: "Ray Gralak \(Groups\)" <groups3@...>
------------------------------------

To UNSUBSCRIBE, or for general information on the ap-gto list
see http://groups.yahoo.com/group/ap-gto
------------------------------------

Yahoo Groups Links

<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/ap-gto/

<*> Your email settings:
Individual Email | Traditional

<*> To change settings online go to:
http://groups.yahoo.com/group/ap-gto/join
(Yahoo! ID required)

<*> To change settings via email:
ap-gto-digest@...
ap-gto-fullfeatured@yahoogroups.com

<*> To unsubscribe from this group, send an email to:
ap-gto-unsubscribe@yahoogroups.com

<*> Your use of Yahoo Groups is subject to:
https://info.yahoo.com/legal/us/yahoo/utos/terms/