Re: [ATM] FW: Secondary Cage Calculations

[Alexis Cousein <al@sgi.com>]

Geogre Nikolidakis wrote:
> I know I am new to ATM forum but applying some Geometry
> I found this formula.
> Ring ID = Aperture + 2 * Tan (AFOV/2)* A 
> Where A= distance from top ring to primary mirror.
> 
Exactly. Now, if you take A ~ F and tan(a) ~ a,
and fill use the image height vs. angle
relation in the focal plane,
that becomes:

RID = Dmirror + Field_Stop

QED.

But you can make A<F (especially with a ring and a light
shield at the other side that is on the outside of the ring),
and you can use a small field stop (i.e. use a small angle)
in this formula without affecting the illumination at the
edge as much as if you picked a small field stop for
sizing the secondary, i.e. you need to be less conservative
in sizing the fully illuminated field for this kind of vignetting.

-- 
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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