I would first get a newt. under my belt before doing a cass. as the cass needs to have a convex mirror built and also the primary cored unless you redirect the light out the side.
As to the different designs, I suggest that you get the book "Telescope Optics - Evaluation and Design" by Rutten and Van Venrooij from Willmann-Bell. Cost of the book is $25 and there is software for the book at another $25 and I would suggest that if you're planning on building a cass. you get the software so that you can easily define the surfaces that you are going to have to build.
The Dall-Kirkham is probably the worst of the cass. designs for off-axis views as it's got a lot of abberations.
The secondary is going to be relatively difficult to build and test as it's a convex surface rather than the concave surfaces so many build but you can do it if you really try. Testing is the difficult part.

• testing - glasspusher - October 1, 2001 - 00:56 UTC