Re: [ATM] couder cassegrain

["Bob May" <bobmay@nethere.com>]

Unfortunately, the Coude Cass is in the second edition of Texerau which I
don't have.
The Coude focus is merely taking the light path off from the axis and
putting it out the side of the scope ala the Newtonian configuration of the
basic parabolic mirror telescope.  This flat mirror will reduce the light
power by the reflection loss of the mirror and will also increase the
aberrations of the system by the errors in that flat mirror.  Contrast loss
due to light coming in past baffles will be less as the eyepieces will be
seeing the far side of the telescope tube rather than looking towards the
sky past any baffles that may be present.
The other advantage with a Coude focus point is that the primary won't be
cored (a scary job on any finished telescope mirror as you're using large
grit around a polished surface) and the eyepiece will be at the side of the
scope where you can get access to it without lifting the scope way up.
I'll note that putting a large folding flat on a Newtonian telescope is
going to be much worse than the large secondaries that people complain a lot
about already and that will really reduce the contrast of the image in a
real way that will be readily visible to the eye.
Bob May
bobmay@nethere.com
http://nav.to/bobmay
http://bobmay.astronomy.net

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