Re: [ATM] Secondary Cage Calculations (formula from Kriege +Berry's book)

[Alexis Cousein <al@sgi.com>]

Robert Houdart wrote:
> 
> If you want a larger fully illuminated FOV you should increase the ring
> ID. 
> 
And increase the secondary size (and central obstruction), because
otherwise the fully illuminated field will tend to shrink.

In fact, it's often useful to allow some vignetting from the front to
reduce vignetting from the secondary, if that secondary
  isn't sized to give full illumination for all eyepieces.

At least if you want to keep the central obstruction small (which is
harder for small fast scopes than for slower or larger scopes).

> In essence the impact of choosing a slightly smaller or larger ring will
> be fairly insignificant, both for the optical performance and for the
> cost of the telescope.

Yup.


-- 
Alexis Cousein                                  al@sgi.com
Senior Systems Engineer/Solutions Architect     SGI/Silicon Graphics
--
<If I have seen further, it is by standing on reference manuals>

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