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Old 10-07-2010, 07:31 PM
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multiweb (Marc)
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SCT visual alignment

I thought I'd share this tip with any SCT user out there. I've been using it for a while but never figured out how to explain it or even take a photo of it until now so here it is. All you need is some flute panel (Bunnings) and to draw a cross with two concentric circles on it. One circle is slightly bigger than your primary mirror and the other circle is slightly smaller than your secondary mirror.

You all know the trick of standing 6 feet in front of your SCT in daylight, close one eye and peek at those concentric reflections to see if your optics are reasonably well aligned. Well this is the same idea but a bit more precise because you're looking through a small 4mm hole and you have some kind of reference on the panel in the form of circles and lines that you can use to align the board very accurately to your scope then you can get a very good visual feedback about the position of your secondary, position of corrector, any offset really.

Anyway pictures are worth a thousand words so have a look at the three shots. It's pretty self explanatory.

PS: In this scope I pushed the corrector to the 9 0'clock position and star tested it. So the scope is optically aligned and collimated but you can see it is not mechanically because I did offset the corrector on purpose. The photos are as close as I could get them. It's hard to image something through live view that you usually assess through a pupil exit hole visually.
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Last edited by multiweb; 10-07-2010 at 07:49 PM. Reason: spelling
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Old 10-07-2010, 08:00 PM
Dennis
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Hi Marc

Thanks for the report and photos – I’ll give this a try with my C9.25 and see what I get. A great set of illustrative images through the 4mm aperture!

Cheers

Dennis
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