Re: [ATM] Cassegrain Secondary Magnification

["Alfredo Rainho Neves" <arainho@snowsoft.biz>]

Hi Ken,

 

I am not quite sure that is true. Don't remember where I read it but the
aberation will not be magnified, because what is important is the
differences in the optical path length and that is not changed by the
magnification of the secondary.  

 

Regards,

 

Alfredo

 

From: Ken Hunter [mailto:atm_ken_hunter@yahoo.com] 
Sent: Sunday, February 24, 2008 8:48 PM
To: Alfredo Rainho Neves; atm@atmlist.net
Subject: Re: [ATM] Cassegrain Secondary Magnification

 

Alfredo...

 

Remember that the lower the primary focal length the harder it is to make.
Any abberations left on the primary will be magnified by the secondary as
well as the image size.

 

Ken Hunter



Alfredo Rainho Neves <arainho@snowsoft.biz> wrote:

Hi,

I am trying to design a short tube, long focal length cassegrain (planetary
scope) and would like to know what are the disadvanteges of having high
secondary magnification factor. For example what would be the disadvantage
of having an F1.5 mirror in an F15 cassegrain (10x secondary magnification)?
I do realize that an F1.5 parabolic primary is a challenge. Anyone care to
comment.

Regards,

Alfredo


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