Re: 1st try with EXOS2-GT Did not go well

Steven Romero

This procedure worked for me very well tonight in Houston.

First night to align the scope after playing around with and figuring out kstars earlier this week inside the house. Even with the bright city lights of Houston I was able to find the Polar star and get a decent fix. Probably not good enough for AP but for viewing its fine.

Kstars works very well too with my Mac. I tested the alignment by hitting a few targets despite the clouds. Looks good to me.

Thank you Robert!


On Thu, May 28, 2020 at 6:09 PM Robert Parks <dionyxian@...> wrote:
My first night experience exactly.

So I will save you, or attempt to save you, months of searching Youtube, Cloudy Nights Forums, the ES PMC8 user group on, and try to give you some tuning steps you must take with the equipment before it is useful to you.  These are basic equipment tuning steps.  

First -  the legs must be always spread as far as possible and the nut cinched up tight under the spreader.  Rigidity is the key.

Second:  the mount must be level every time.


Third:  The polar scope has to be aligned to the right ascension/polar axis of the mount.  This is a daytime job, where you take the mount, set it up  (without any equipment on it) so that there is a distant tower antenna or some such point you can see in the polar scope, and then adjust the altitude and azimuth bolts until the distant object is under the crosshair of the polar scope,  You then loosen the clutch and rotate about the polar /right ascension axis to see if the object says put under the crosshair.  If it moves, you have to adjust the polar scope's axis.  There's a good online video showing the concept and technique with a different telescope here:

Fourth:  it is been my experience that you have to adjust the dovetail plate or whatever interface you have on your equipment to make sure that your optical equipment is lined up with the polar axis as well.  After you've got the polar scope in line with the mount's rotational axis as in the third step, set it up in the evening. (Remember -legs tightly spread and level the mount).  Put Polaris under that crosshair using the altitude azimuth bolts.  With your gear mounted, look through the viewfinder/ eyepiece.  If Polaris is not in the center of the field of view, you'll need to take allen wrenches to adjust the mounting plate on your camera/scope until it lines up.

Now after all this tuning is done, it is time to actually do a polar alignment and try to get some goto performance.

Polaris isn't the thing that you want the mounts polar axis directly aiming at - Polaris itself rotates around the "North Celestial Pole".  Think of Polaris as a dot on the end of the hand of a clock, and the actual NCP as the center of the clock.  Depending on the time of the year, Polaris can be at 3:00 w/r/t the NCP, or 6:00, etc.   That is called  the "hour angle" of Polaris.  I use a smartphone program called Polar Scope Align.

image.pngIt has a small circle showing where Polaris is supposed to be in relation to the NCP. Polaris circles the celestial pole at a distance of approx. 40' . 

The reticle of the polar scope in the mount looks like this:

You will want to look through the polar scope, and rotate the R/A axis until the little circle (on the line below the crosshair) is at the proper hour angle with respect to the crosshair, Then, use the alt/az bolts to place polaris in the little circle.
Hour Angle.jpg

Congratulations, you now have a calibrated, polar aligned equatorial mount.

Loosen the clutches and put the index marks back together and look through the viewfinder - you should see polaris.

I'll have to defer to Wes and Jerry to assist you with any astrophotography stuff.  I do strictly visual, so the above is good enough for me to get a 2 star alignment done with Explore Stars and get in the ballpark with goto's  

Pointers - make sure your time and location are correct for your location on the explore stars app.  Also, make sure you "reset alignment" at the beginning of your session, before doing any 2 or 3 star alignment.

I learned with Explore Stars, but eventually got a Dell micro computer off Ebay (Venue Pro 10 for about 100 bucks), a USB to Serial cable with the FTDI chipset, installed the PMC8 configuration manager, ASCOM Packet, Stellarium Scope and Stellarium and went that way.

Folks hereabouts are friendly and we've all been there.  Good luck.

Robert Scott Parks

On Thu, May 28, 2020 at 4:36 PM Bob Schoner <rschoner@...> wrote:
New to the forum. Do a lot of landscape photography and figure since I can't go to far away places to take pictures I could still take pictures of far away places. So, after much searching I picked the EXOS2-GT as my first mount. It has GoTo and is reasonably portable (Backyard and motorhome). I did the usual living room setup and things seemed to work well with Explore Stars and my laptop. Last night I tried it out for the first time. Polar alignment went surprisingly well. Lined the mount with Polaris by eyeball, looked through the Polar Scope and there it was. Too anxious to do a star alignment so I tried to slew to the Pinwheel which was directly overhead. It moved to low in the sky to the northeast. Then tried a 2 star alignment. Started with Merak since the big dipper was directly overhead. Again the mount slew to low in the sky to the northeast. I have since checked the time and lat/long and they are correct for my location east of Sacramento. Double checked that the black arrows are aligned on the mount.
The instructions say to center the alignment star in the viewfinder (Canon 7D with 28 to 135 lens set to 28mm) but it is so far off that I can't do that.
Is it normal for the initial alignment to be this far off? Or am I doing something really wrong?
Any advice would be appreciated.

Bob Schoner

Robert Scott Parks - Northwest Arkansas, USA

Mount: Explore Scientific EXOS II GT WITH PMC-8
Polar Finder: EXOS II integrated with illuminated reticle
Telescope: Explore Scientific 127mm f/7.5 FCD1 Air-Spaced Triplet ED APO Refractor
Finder: Telrad
Hardware: Samsung Galaxy Tab A 7", Dell Venue 10 Pro 32bit OS, Samsung Galaxy S20+
Steering Software: ExploreStars App, ASCOM/POTH + StellariumScope/Stellarium + Wifi Scope + SkySafari Pro

Steven Romero
Location: SE Texas
Mount: EXOS2-GT PMC-8
Scope: ED102 APO

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