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Re: [ATM] convex secondary


----- Original Message ----- 
From: "Richard" <cnc@cncservo.co.uk>
To: "Jonathan Lavoie" <atm@atmlist.net>
Sent: Tuesday, March 01, 2005 11:59 AM
Subject: Re[2]: [ATM] convex secondary


> Hi Jonathan,
>
> Tuesday, March 1, 2005, 4:15:28 PM, you wrote:
>
> JL> Why wouldn't the secondary be 4", I tought the only difference between
> JL> Cassgrain and RC was the figure of both primary and secondary mirrors?
>
> If you are still using your tertiary diagonal mirror and can get
> away with the -2" back focal length, then to cover field of your
> camera sensor the secondary needs to be 4.12" diameter.

Are you sure? Even is the on-axis lignt cone is less then 2" ? (The terciary 
located at 19" from primary surface or 17" from the focal plane)




>  Have you tried ray tracing this in
> MODAS or similar?. The figures I'm quoting above are based on :
>

I downloaded MODAS but not used it yet. Will have to learn...

Thanks,

Jonathan

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