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Old 06-12-2018, 09:27 AM
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JohnG (John)
Looking Down From Above

JohnG is offline
 
Join Date: Dec 2005
Location: Cootamundra, NSW
Posts: 1,709
I have been getting a similar arcs when pointing in some directions, with help from another member here I had thought I had tracked it down to the edges on the shutter aperture of my dome, I thought it may have been light from a rather bright street light reflecting off the edges, I blackened them but a test still showed the arcs.

I then shone an averted light down the tube from the front and saw a major reflection coming off the front of the draw tube. The focuser is a Moonlite and the end of the draw tube is an anodised gloss black. I have taken the Moonlite off and now have the original Takahashi focuser fitted, it has a matt black end piece on the draw tube and I can't remember ever seeing these arcs from it.

Whilst I only did this yesterday, I haven't had a chance to test as yet due to clouds last night but I believe this to be the culprit and hopefully will be testing again tonight.

Sounds to me like you are having the same problem with an off-set star reflecting light off the end of the draw tube, I would think about taking the focuser off and blackening the end of the draw tube.

Cheers

John G
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