Secondary Size for 6" f8Posted By Mike Hosea |
With the elliptical secondary the measurement of interest is the minor axis. That corresponds to the obstruction diameter when it is mounted at a 45 degree angle.
I figure the actual size by looking at the illumination levels off-axis and considering the type of observing that I would like to optimize for. Mel Bartels has a calculator at
http://www.efn.org/~mbartels/tm/diagonal.htm
But SEC makes the comparison easier (see middle of page at)
http://skyandtelescope.com/resources/software/article_328_1.asp
Probably both 1" and 1.3" would be reasonable depending on your preferred type of viewing. 1" is a little aggressive, 1.3" a little conservative. Improvements to better than 1/10 wave would be very subtle or nonexistent, depending on your primary. The better the primary, the more I would be willing to spend extra on the secondary.
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Mike
I figure the actual size by looking at the illumination levels off-axis and considering the type of observing that I would like to optimize for. Mel Bartels has a calculator at
http://www.efn.org/~mbartels/tm/diagonal.htm
But SEC makes the comparison easier (see middle of page at)
http://skyandtelescope.com/resources/software/article_328_1.asp
Probably both 1" and 1.3" would be reasonable depending on your preferred type of viewing. 1" is a little aggressive, 1.3" a little conservative. Improvements to better than 1/10 wave would be very subtle or nonexistent, depending on your primary. The better the primary, the more I would be willing to spend extra on the secondary.
--
Mike