Re: Polar Alignment #EXOS2 #polaralignment #ExploreStars


Joe Izen
 

I have a suggestion for those trying to polar align an iExos-100 visually using the bore hole in the right ascension axis that I haven't seen on the group. I had more practice than I care to admit after bumping my tripod. 

1) Adjust the tripod legs so the bubble level shows the mount is level.

2) Set the latitude adjustment to set the latitude on the west (east) side of the mount for northern (southern) hemisphere observers. The bore hole has a 2.5 degree field of view, so your latitude adjustment should be dialed in more precisely. 

3) Rotate the RA axis so that the scope is out of the way. Loosen the azimuth knob and sight over the scope to get close.

4) Return to an approximate home position, then rotate the scope 90 degrees on its declination axis to line up the hole in the declination axis with the RA axis bore tunnel. (Embarrassing how many times I forget this key step and stare down a blocked tunnel!)

5) Crouch and spot the polar star alongside the scope with your dominant eye closer to the mount. Your dominant eye is the one you use to look through an eyepiece. With you eyes fixed on the polar star, slid your dominant eye over to sight through the bore tunnel. Chances are, you won't see the pole star unless you are very lucky. However, if your eyes have held their alignment, you will see an image of where the pole star would be if the mount were transparent, superimposed on the wall of the bore tunnel. If your leveling and latitude entry are good enough, you can rotate the azimuth and spot the pole star at the end of the tunnel. You can test if you've succeeded by closing your non-dominant eye.

6) I am rarely lucky. I usually have to adjust both the latitude/altitude and the azimuth.

7) This two-eye method is a skill that one gets better at with practice. It is tricky to do the first time. It does get easier, but the bore tunnel will never be as easy as a proper polar alignment scope. It requires a bit of patience to do the alignment. If frustration gets the better of you, there was an interesting suggestion in another thread to use a gunsight laser stuck into the bore hole.

8) If you aren't driving your mount with a computer, you will want to go through this visual polar alignment, and something like Wes' home-position finding algorithm (in another thread.) There are some ExploreStars gotchas that cause ExploreStars to switch to RA-only tracking.  The drift is a bigger issue for PMC-8 than with traditional mounts with hand paddles that only do RA tracking. Hand paddles like SynScan offer a polar alignment routine that do much better than visual, bore tunnel alignment, and some of the mounts have polar telescopes which add to cost, but work better than the bore tunnel. In principle, a polar alignment routine could be written for ExploreStars by the ES team or a PMC-8 user who had the skills (I don't). A polar alignment is remains high on my feature list-wish.

Last night, after spotting Polaris and offsetting it as best I could by eye, I read my mount's latitude marker at 31 degrees, even though I was observing at 33.0 degrees. I was more than the 1.25 degree half-width of the bore tunnel off.  Jerry, is the offset due to the intrinsic precision of the level? The latitude marker's calibration precision? The bore tunnel alignment? Operator error?

Joe

 

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