Have you ever thought about why your Newton telescope has the dimension it has, primary and secondary mirror, focuser, f/number and so on?
I stumbled in to this tool Newt-Web that Kenneth H. Slater has developed further from Dale Keller's code. It's an online design tool page for Newton telescope.
It's a very intuitive page where you can put in some figures about a Newton telescope that you want to built and get back information about it's performance. It give a ray trace and important data back. From that you get understanding when a Newton telescope design is good or not.
I have done some test and written it down on my homepage so you can see the different steps and my comments:
http://astrofriend.eu/astronomy/proj...telescope.html
I already know some of the physics and math, but never got to know so much in short time what happens when you change a parameter and what happens inside the telescope. Beware, I'm still in the learning process and not all what I have written is fully correct.
I recommend you to take a look at Newt-Web page even if you never will built a telescope, you get knowledge and understanding that could be very valuable when you shall buy a Newton telescope.
/Lars