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three points should do the job. I have a Skywatcher 10 with 3 point support and it works exceptionally well - the mirror can move around by a few thou on three cork supports and is located by 6 felt edge support stops.
For an imaging system (not for visual though), with a 10 inch mirror you really don't need to be too concerned with slight distortion of the optics - you will rarely get better than 2 arcsec FWHM seeing and even slightly imperfect optics can do much better than that (eg 1/3 wave optics is going to be indistinguishable from perfect optics most of the time).
The biggest problem may be the secondary mounting - astigmatism is the issue. Chinese secondaries can be pretty thin and bendy - a thicker (premium) secondary with high reflectivity coating is probably worth the money
Last edited by Shiraz; 27-10-2014 at 12:09 AM.
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