Problems with focussing

As long as you have not focussed your scopes there is no result whatsoever. Period.
I can only describe my own equipment of course.

So in my case this is about the Askar Guide scope and the main Celestron. But this last ones focussing depends on the used camera or better: the actually used optical train.

The guide scope is the easy one: it takes a small guide camera. At the end of the scope the camera can slide in. Point it in daytime at a distant object, set the focus ring in its center position, slide the camera in while you observe its image on your computer. When as sharp as you can get it fasten the screws secure. Now fine tune the focus ring. The guide scope is now focussed and ready.

The main scope is different. Focussing depends on the optical train. In this case I use the ZWO ASI2600 MC Pro which needs about 133mm of back focus. First… that back focus distance is arbitrary. Up to 2mm difference is no problem.

On my Celestron Edge HD*” I have the EAF controlling the focussing mirror. So first thing to do is get a crude focus but make it as good as you can and this has a very important reason: like the Newtonian the SCT scopes produce donut shaped stars when enough out of focus. The StellarMate uses Ekos routines to focus and it seems to hate donuts. However… there is the donut buster. So activating the donut buster is one thing but also try to stay within the focus range in which the stars don’t get to form the donuts. So the better your crude focussing the less change the software goes focus hunting. It also causes the focus time to speed up significantly. I have set the parameters to low values specifically the amount of steps per focus action and the maximum travel length of the EAF.











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