Getting an accurate home position

[Guest]

I don't have a permanent place for my scope. I have take take it in and out each time and I'm trying to shorten my set up time. I have an heq5 mount and the software I use is eqmod, apt and carte du ciel. I use polemaster to set up the polar axis and find that pretty good. I've marked up the home position on the mount as accurately as possible but even so the first object I go to is always fairly close but still a bit off and some time is taken getting the scope lined up. I had an idea about getting the home position more accurate.

I've marked up the home position on the scope using a method I found on youtube. At the end of each observing session I always send the scope back to the home position ready for the next session. My idea is to use plate solving to get the scope pointing dead on to the astronomical north pole at the home position. APT has an add on which I think can be used to automatically plate solve and make corrections until it's very accurate. I haven't tried this yet. But if I could do that and then switch the mount off then on again. That should be an accurate home position. Providing I always send the scope to the home position before switching off then when I start next time and after doing the polar alignment it should go more accurately to the first object.

The reason for the question is that I think I read somewhere that there are problems with alignment close to the astronomical north pole.

Cheers

Steve

 

[almcl]

48 minutes ago, woodblock said:

My idea is to use plate solving to get the scope pointing dead on to the astronomical north pole at the home position. APT has an add on which I think can be used to automatically plate solve and make corrections until it's very accurate. I haven't tried this yet.

APT has three possibilities with plate solving: All Sky Plate Solver (ASPS), PlateSolve 2 (PS2) and ASTAP.  Once downloaded and installed with correct index files PS2 is very quick to solve provided you are fairly close to the target.  ASPS will solve almost anywhere but takes a little longer in my experience.

However, why bother refining the home position?  Instead, set up as normal, goto your target (or a nearby bright star for focusing purposes) and plate solve that.  Sync and then ask CduC to goto the target.  In my experience it is then almost always dead center in the frame and has taken under two minutes to achieve.  A good home position is not to be sniffed at, but it's probably not worth wasting valuable imaging time over.  Of course if you can do this before Astro Dark, it helps while away the time?

[Guest]

Thanks, I understand what you say. My idea was that I would only have to do the plate solve at the pole once and providing I always ask eqmod to return to home at the end of each session it should be good on all subsequent sessions. I have messed around with plate solving via APT but only on saved images. I've not often been successful with ASPS but PS2 usually works ok. I've not used ASTAP because I was using an older version of APT. I've recently updated and I should be able to try it now.

My aim is to try some work on variable stars and one problem I have is that I usually can't see the target star in live view so I'm trying to point the telescope at something I can't see.  Also sometimes the star is not even shown on CduC so I can't click on it and ask CduC to go there.  What I was hoping to do was to sync on some brighter stars around and then ask it either through APT or CduC to go to a specific RA/DEC.

[Dr_Ju_ju]

Accurate home position isn't required, as long as your roughly aligned, i.e. weights down & scope pointing toward Polaris, and you've polar aligned the mount, then slewing to target & plate solving is all that is required....