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Re: [ATM] how good is this mirror?
Hi Richard,
>is also very fast at f/3.69, so it will give poor performance
>with bad coma.
I presume you mean that the bad performance is due to the horrid wavefront error, not the f/#. I have observed thru 28" f/3.7 mirrors which are very well figured, and they give very good images on-axis (you would think you're looking thru an f/6). Yes, there is coma off-axis, but it is not horrible (it would be horrible if the mirror was not figured exceedingly well). So it seems to me that the main off-axis image problems are due to the refractive elements not handling the light cone (higher-order astigmatisms in the IP).
No matter what speed it is, a perfect parabola will give a perfect image on-axis.
>There also aren't many eyepieces, even expensive
>ones, that will deeal with f/3.7.
I would really like to know which eyepieces & coma
correctors WILL handle f/3.7. Anyone know?
Thank you,
John
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