Re: ATM Dall-Kirkham Cassegrain Questions

[Bill Marriott <btk@pacbell.net>]

Bennett, Thomas D wrote:
> 
> Hi Everyone,
> 
>. I'm thinking of making a 9" F40 Dall-Kirkham
> Cassegrain with a F5 primary and 8X secondary.

  My questions are:
> 
>         (1) Would a 9" F40 DK-Cass make a good planetary scope?

I have been told that long focus Cassagrains have problems with
baffeling being unable to prevent background light from entering the 
light path between secondary and focuser.
 
>         (2) Is the DK-Cass a do-able project for a novice glass pusher?

The convex secondary is do-able,  depending on one's skills, but one
must also accurately produce the proper correction for the ellipsoid 
primary. I heard somewhere it is approx. 70% of the correction required
for the equivilent paraboloid, and I'm sure others on this list can be
more specific.

> 
>         (3) Is the Foucault test (I've ordered University Optic's > tester) precise 
>enough for me to get a good figure on the F5 primary? > I choose F5 because I read that 
>a faster primary would be extremely > difficult.

Yes, though the Univ. tester can use a little upgrading to get it to
perform accurately.


> 
>         (4) Is the 1.25" sphereical secondary going to be difficult to make?
> - A friend suggested that I could just purchase a bunch of Edmund
> plano-convex lenses with the proper curvature; pick the best and one and
> figure it if neccessary and get it aluminized.

Sounds possible



>                 Any advice you could provide would be helpful - Thank you -
> Tom Bennett


Any Cassagrain is a lot more work than an equivilent Newtonian.
I, like many others, have a unfinished Cassagrain in my closet.
(This was to be a f25 Classical Cass)

Good luck


-- 
Bill & Tracy Marriott
Woodacre, Ca. USA
btk@pacbell.net

http://www.starlightoptical.com
Telescope/Optical Stuff

And now,  P1800 Volvos
http://www.starlightoptical.com/volvos.htm