Re: [ATM] Secondary Cage Sizing?

["Jan van Gastel" <jhm.vangastel@wanadoo.nl>]

You have a very large fully illuminated field. This is only necessary for a
2 inch wide field (84 degrees) eyepiece of 31 mm focal length, if you don't
want to let the illumination drop below 70% at the edge of the FOV (which is
good).

Personally, I wouln't design a telescope around my widest field - lowest
magnification eyepiece, because I use medium to high magnifications 99% of
my observing time. But this might be different for you of course.

Jan
http://home.wanadoo.nl/jhm.vangastel/Astronomy/
----- Original Message ----- 
From: "MATTHEW SIMMONS" <msimmonsmcse@msn.com>
To: <atm@atmlist.net>
Sent: Sunday, April 18, 2004 5:49 AM
Subject: [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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