Re: Secondary centered in 8" Edge
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There is no requirement for spherical SCT secondaries to be centered w.r.t. the primary apart from enabling uniform field illumination. This is because, being a sphere, a decentered secondary can have its axis aligned again by merely tilting it. Centering of the corrector, however, is critical. Decenter it and you'll get astigmatism. I would leave it alone. You can't possibly observe the difference in field illumation from such a small decenter.
Tanveer.
On Wed, Mar 5, 2014 at 1:11 PM, Howard <feeways@...> wrote:
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Stan
Thanks for responding.
I use metaguide software and webcam to get very fine infocus collimation nailed in my poor seeing. Defocused the doughnut is not centered though...i guess cause the mirror is not centered.
I know this does not affect the view as i observe infocus obviously.
However, it annoys me.
What is the way to center that secondary? Adjust the corrector or remove and center the secondary in the corrector itself?
Howard
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It may be of little or no consequence because the spherical secondary need not be exactly centered for optical integrity.? SCTs are fairly?tolerant of both secondary decenter and primary tilt.? "Edge HD" is probably a bit less tolerant due o the internal corrector lenses.
Do a good star collimation then assess the image.
Stan
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Tanveer Gani