Quote:
Originally Posted by troypiggo
James, could I ask for more detail about how you're ensuring focus, what drastic action etc? To do with primary, focuser, or both?
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I need to store my scope horizontally so I can close the observatory roof. I was finding that the mirror was tilting forward during the day and then settling back down into the cell as the night went on (and also jumping around at times). I knew it wasn't thermal contraction because it was going in the wrong direction. The cell had small pads on the back that can expand and contract. Also only one of the 3 points on each triangle was stuck to the mirror, the other 2 were free to separate from the mirror, allowing the mirror to fall forwards. To make it worse, the mirror clips on the side are angled forwards too, so when the scope is horizontal, the mirror really tilts forward a lot. The solution was to glue the mirror to each triangles with 3 blobs of silicone. Simple and easy. I also "tightened" the mirror clips, so they just start to grab when I slide a piece of paper between the clips and the mirror. Since this a standard GSO newt, I suspect the all have the problem.
To my amazement, I found the tension screw on the bottom of the focuser works loose every night. I couldn't believe it was true (or possible) so I drew a little arrow on it, and sure enough, in the morning I could see that it had unwound itself about 1/4 of a turn. I still can't figure out the mechanics of how that is possible, but it happens. So I used some sticky tape to hold it in place.
These are both simple things really, but it takes time to sort them out one by one.
I wrote a little program to extract data from my focusmax logs so I could see what is happening using excel. The attached graph shows the before and after of how the scope holds focus. Yes there is still room for improvement, but at least I have a chance now.
James