Optics-Talk-With-MikeL

My name is Fred Rockenberger.  I got your name from Andrew Aurigema 

> while talking to him about setting up a casting works.

Sounds like a lot of fun. Andrew has told me a little about it.

> I am coming into possession of an ~F/5 20 inch cassegrain mirror. It > has no corrector plate or secondary associated with it. > What kind of money is involved in making the aforesaid?

Corrector plates are expensive, and I haven't made one yet, but I plan to in the future. I have made several classical Cassegrain secondary mirrors, and I will be refiguring Andrew's in the near future. A corrector plate is not necessary for a classical Cassegrain.

Permit me to ask you a few questions about the use of the telescope. I have no idea what you know about telescope design, so I apologize if you have already worked through some of these issues.

What will the telescope's purpose be? What is the desired system focal ratio? What are the constraints on weight and length of the tube? Have you considered designs other than a Cassegrain?

If the primary mirror is F/5, that's a bit long for a normal Cassegrain, especially in that size. The final focal ratio would end up at F/15 or F/20, probably, and that's a very high power system. It also means the telescope's tube will be as long as a 20" F/4 telescope.

Mike L.