Exos 2 pmc 8 goto precision issue #EXOS2


Jeny@
 

Hi, I’m working on making my EXOS-II with PMC-8 mount to more precisely point on objects when using ExploreStars on Windows.
My best result so far is around 1.5 degrees off the target – that is in the FOV of mine 9x50 finderscope. I’m able to recenter if target is a bright objects, but on faint objects it’s getting much more challenging.

I looking for some advises on how to improve my GO-TO pointing precision.
I do level my mount and do precise polar alignment using Polemaster before doing 2 or 3 star alignment.
I did verify RA/DEC alignment – seems like DEC alignment is in sync with marks on the mount, but RA was a little bit off and I had to remark it.

Interesting pattern, when doing 2-3 star alignment, goto on object after 2-3 star alignment, or just goto to object like planet before 2-3 star alignment – telescope is always get pointed about 1.5 degree to the right of a target.
It's almost like alignment does not add any accuracy to goto,

 

Thanks!

Jenya


Wes Mcdonald
 

Jenya

In my experience, after aligning with Polemaster, my goto is best if I do not do any alignment.  That is, the polemaster gets your mechanical alignment just right.  If you are using iOS or windows then do a subsequent SYNC on a star after centering it using the LRUD buttons. If you have Android there is no SYNC button (correction is in work I believe).  I would use something near about 0 Dec and near meridian, but about any star will work.  That sync will take the home error out and leave you with a good alignment.  If you are doing a deep space space dim object that is invisible in your finder/red dot, do a sync on a nearby star and your go-to will we bang on.

If using Android you can do a pretty good sync, I think, manually.  After polemaster, point to a star near your object of interest.  Then break the clutches and manually center the star and reclamp the clutches.  Subsequent goto should be really good.  For this adjustment do not use the LRUD controls, do the manual adjustment.

Last thoughts, if you have a really bad cone angle your go-to performance after a sync will be best near the sync location and fall apart as you move away.  In that case just keep doing a sync near the object of interest on a star you can see (after you center it with the LRDU buttons or via the loose clutch method) and the subsequent goto to a nearby dim object will be very good.

So in summary, two ways outlined after doing a good physical alignment with a polemaster:

1.  Use the software SYNC button in Explorestars on a bright star after centering with the LRUD buttons or

2.  Perform a manual sync by centering a star in the eyepiece by loosening the RA and DEC clutches and manually centering it.

Wes


--
Wes, Southport NC
PMC-8, ES ED 127, 10" LX200GPS, Astro-Tech 8" Newt, ETX-90
Polemaster, Orion ST-80 and SAG
Electrical Engineer, Retired


Jeny@
 

Wes,
Greatly appreciate your input. I'll try soft/hard sync approaches to make the mount goto on target with acceptable accuracy.
Do you know, is it possible to adjust exos-II to fix that 'cone angle' error without modifying the mount, I mean by some screws adjustments?

Thanks,
Jenya


Wes Mcdonald
 

Jenya

The cone angle to worry about is with your telescope and its vixen bar.  You will find adjustment screws on the bar perhaps to use to adjust it.  In practice if the scope is bolted directly to the vixen bar there should be very little cone angle.  If the scope is in rings with three screw mounts then the cone could indeed be pretty terrible.

If you search the forum you will find a video Jerry posted regarding how to adjust cone angle.  

If the telescope is mounted directly to the vixen, that is without adjustable ring mounts, the cone error will certainly not give you a problem if you SYNC anywhere near your dim deep space object.

Wes

--
Wes, Southport NC
PMC-8, ES ED 127, 10" LX200GPS, Astro-Tech 8" Newt, ETX-90
Polemaster, Orion ST-80 and SAG
Electrical Engineer, Retired