Bolton Astronomical Society

"Wandering" polar-scope issue
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Author:  rwilkinson [ Sun Mar 26, 2017 10:46 am ]
Post subject:  "Wandering" polar-scope issue

I've noticed during my imaging sessions this week that my declination-drift has been poorer than usual, so I was suspicious that the polar-scope which I use for alignment needed re-setting.

But when I checked it this morning (using the antenna on top of the street-lamp across the road as my reference-point), I found that my target was "wandering" around the reticule as I rotated the polar axis, but never returning to the same point. :?

After stripping it down, I discovered the problem: the collar which locks the polar-scope's helicoid focusser (see picture) had worked loose, and there was then enough play in the thread that the objective-end was "drooping" under gravity!
File comment: The focus-locking ring on my polar-scope
polarscope.jpg [ 125.02 KiB | Viewed 3691 times ]

After I tightened this collar, the 'scope was good and solid again and when I re-fitted it in the axis, the fixed target described a small circle in the reticule. I've now re-calibrated it so that there's very little movement in the target, and even tightened up some slack in the polar axis whilst I was at it.

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