How to build a Cassegrain with unperforated primary mirror

Design:

You can build an unperforated Cassegrain as I did, first thing, you will need the formulas for a Cassegrain

Points to consider:
1. Primary mirror's diameter (D₁)
2. Primary mirror's focal length (F₁)
3. The whole focal lenght (E.F.L.=F₁xM)
4. Secondary mirror's diameter (D₂)
5. Obstuccion caused by the secondary mirror (%)
6. Secondary mirror's gain (M)
7. Image distance behind the objetive (e)

What do you want? A terrestial aplication telescope or an Astronomic one? There is a big diference inclusive, how far do you want to go?

I'm sure you will look for a telescope that allow you planetary observation, are you agree with sacrifice visual field in order to gain amplification? Have you decided wich mount will you use?

You have to calculate p and p' Cassegrain's values and secondary focal lenght (F₂):

                                                    F1 + e
                                                p = ______
                                                    M + 1

                                                p'= p x M

                                                       p'
                                                F2 = _____
                                                     M - 1

Get here your telescope values with this form

                                                     x2
                                                y = ____
                                                     4f

For secondary mirror we will need a convex plane, an hiperbola.

                                                          y2
                                                x2 = (1 + __ ) a2
                                                          b2

                                                b2 = c2 - a2

How ever, in practice, we will start with an esphere plane to aproximate the desired planes.

                                                r2 = x2 + y2

BIBLIOGRAPHY

• HOW TO MAKE A TELESCOPE
  By: Jean Texereau
  Published by: Willmann-Bell,Inc.

• ALL ABOUT TELESCOPES
  By: Sam Brown
  Published by: Edmund Scientific.

Primary mirror with mask

Secondary Mirror, only the center will be used

Tool for primary mirror

Hand made Ronchi tester