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Originally Posted by avandonk
I was under the impression that SN telescopes were designed to minimise the coma inherent in Newtonian telescopes.So a coma corrector designed for a standard Newtonian would tend to overcorrect if used with a SN.I assume SN means Schimdt Newtonian.In fact any given coma corrector only works well for a limited range of F values, and are more useful at lower F values.Ie F6 or less.
Bert
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Hi Bert,
You are correct. The SN is designed to minimise the coma inherent in low ratio Newts. However, the corrector plate only does part of the job. My scope is an f4, but the SN design corrects the coma to that of about an f6 newt. Visually, my SN produces bright flat images to the edge of the field. However, in digital images, there is considerable distortion, particularly in the corners of the frame. The MPCC is designed to correct the coma in Newt's from f4 to f6, so I thought it would be worth a try. Apparently there is some overcorrection that effects the centre of the frame, but it is so slight as to be unnoticeable. I certainly can't detect it.
There is definitely an improvement over not using it. Check out my Eta Carina taken without the MPCC cf the Tarantula with it.
Cheers