Re: Exos-2gt pmc8 mount alignment

Wes Mcdonald


Ok.  Now I know what you are up to.

1.  I advise you strongly to connect to the PMC-8 via the serial cable, not wifi.  No problems with dropped connections etc.  
2.  You will use the ASCOM platform and the ES Ascom driver for the PMC-8.
3.  APT also will connect to the mount via ASCOM hub.  With APT you will be able to run the mount, the focuser, camera, guide camera I believe.
4.  You will use the PHD2 to guide.  I also connects to the mount via the ES ASCOM driver, using pulse guiding
5.  With an OAG on your scope your ASI 120 should be fine.  You might want to figure your view per pixel and see how this relates to your camera arc secs per pixel.  You can research this on the web but in my view you only need to have guide pixels about 2 or three arc seconds in size which should guide you better than the mount can practically be guided.  But then some Exos-2 mounts can be guided better than others.  Bob Hoskins has posted a paper on how to adjust and tune the backlash and other aspects of the mount that contribute to your ultimate guiding errors.  You can find it in the file section of one of the forum sub-groups.  You might read through it and see what you want to do there.  I don't have an OAG, but with my guide scope and ASI 290MM mini I get about 2.5 arc second pixels and guide between 2 and 1 arc seconds combined RMS.  
6.  For alignment, you will need to use something that gets you physically aligned.  ES does not provide software to do this in ASCOM, but you do have a polar scope on the mount which you can use to align the mount.  IF you don't want to do it that way (I never could) you can add a Polemaster or use Sharpcap with you ASI I believe.  You should look into this, as it is easy to use, inexpensive, and accurate.  I use a polemaster because I already owned one, and it is also a breeze and very accurate -- PHD routinely tells me I am good to a few tenths of an arc sec or better.  Don't know if I believe it or not, but guided images are not disturbed by any polar drift (to the limits of my guiding sessions anyhow)
7.  If you are using APT, you can use the plate solve capability it provides to find your DSO objects, dead center.  It uses Platesolve2 software which you will need to download one time, follow APT manual instruction for this.  APT and Platesolve2 will control the mount beautifully to put objects dead center.  With plate solving, you need not worry about stuff like DEC home error like you do with open-loop gotos in explorestars, for example.  So you don't need my article.
8.  So make sure you polar align.  Then put the mount in its polar home position indicated by the little alignment arrows on the RA and DEC axes.  I colored mine with a silver sharpie to help see the danged things.  Then start the PMC-8, boot ascom, etc.
9  You may want to use a planetarium program such as Stellarium or Cartes Du Ceil (or what ever the danged thing is named).  CdC connects directly through the ASCOM POTH hub to the scope.  Stellarium requires a helper app called StellariumScope.  You can research these and see what you like.  APT at least includes integration with Stellarium that allows you to import target locations from STellarium.  That way you can pick objects graphically in Stellarium, import the object into APT and carry on from there with commanding a slew to the object etc.  All through the POTH Hub which uses the ES ASCOM driver.  It all works pretty well, except for the usual Windows related crashes.

So thats a lot.  Not sure what you have done before in this arena, but you have bought a lot of gear and it sure looks like you will have a nice rig once you get it all up and running.  

I'll send a link to Bob's paper and mine for fun in another note.  I don't trust this editor not to lose my response while I go look for them.


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

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