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[ATM] Secondary Cage Sizing?
So I have a design conundrum here....My specs are as follows:
13.1" f4.5
2.6" (?)
.25" focuser board
1.55" Moonlite Crayford +.25" racked out
So, according to K&B, my secondary cage should be ~13.75" and my illuminated
FOV for a 2" ep sizes the secondary at just over 2.6" So far so good.
However, NEWT says that I will vignette the 75% ray at front aperture. If I
fool with the numbers in NEWT to prevent any vignetting, it will take a
14.75" secondary cage. However, when I run those numbers through the K&B
equations, my fully illuminated FOV requires a 2.73" secondary.
So, should I care more about not undersizing the secondary or vignetting the
75% ray at the front aperature? Which is worse for the overall performance
of the scope?
Matt Simmons
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