Re: PEMPro and accurate polar alignment


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












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