Re: PEMPro and accurate polar alignment
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.
From: ap-gto@... on behalf of chris1011@... [ap-gto]
Sent: Saturday, September 23, 2017 3:21 PM
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?
From: Hemant Hariyani hemanthariyani@... [ap-gto]
Sent: Sat, Sep 23, 2017 1:55 pm
Subject: [ap-gto] PEMPro and accurate polar alignment
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?