parabolic, or hyperbolic

[TobiasLindemann]

Hi everybody,

a friend of mine has a telescope from a unknown manufacturer and we want to improve it. Now it has a very bad star form and much spheric aberration. It is built up as a normal newton, but the primary mirror has a hole in the middle. So the mirror is originally either made for a Cassegrain, or for a RC.  If it is a Cassegrain-mirror I think it is no problem and you can use it for a newton too. If it is a RC-mirror, it is hyperbolic, you know and you need a hyperbolic secondary mirror to correct it. My question is, how can I proof, wether it has a parabolic, or hyperbolic form? 
As a newton it has a very (maybe too) wide apenture of f/2.5 and the corrector is made for at least f/4 and is a very cheap one. So the spheric aberration can be a problem of the corrector. We want to change it with a much better one, but if the primary mirror is hyperbolic, a normal coma-corrector is not suitable.
Any ideas?

Greetings
Tobias

[Carlos Milovic]

Hi Tobias,

I think that you may simulate the PSF of both systems (with a parabollic and hyperbolic mirror) and then compare the shape of the stars with actual images (Zemax and Matlab are two options that comes into my mind... it could even be made with a script in PI).
There should be some simulations on internet too, already made... I'll take a look into some notes I got from some optics courses I had at the university, to see if I have some visual comparisons.

[TobiasLindemann]

Hi Carlos,

thanks for your answer. I will give it a try with Zemax. If you already have some simulations it would be fantastic.

Greetings
Tobias