Re: [ATM] convex secondary

["Jonathan Lavoie" <atm@lavoielactee.net>]

----- Original Message ----- 
From: "Mike Lockwood" <melockwo@uiuc.edu>
To: <atm@atmlist.net>
Cc: "Jonathan Lavoie" <atm@lavoielactee.net>
Sent: Thursday, March 03, 2005 12:07 PM
Subject: Re: [ATM] convex secondary


> Jonathan,
>
> Jonathan Lavoie wrote:
>> Jonathan Lavoie wrote:
>> Around F2.9
>>
>> According to Richard the K is almost -5. Didn't do the calculation 
>> myself... still learning to use the software MODAS.
>
> So that's an F/2.9 mirror with 5 times the correction of a parabola. 
> That's a lot of correction.
>
>> Bad news about my idea of shortening the 16" RoC to use it in a Hindle 
>> test then grind it back to it's good focal length: I forgot that it's 
>> current RoC is twice the F length so if I want to use it as a Hindle 
>> there is a lot of glass that will be removed. So this idea becomes 
>> impraticable.
>
> I thought that might be a problem once I saw that the secondary was 
> F/2.9 - the Hindle sphere ROC has to match the secondary ROC, I believe, 
> and that's one FAST 16" mirror.
>

Both RoC don't need to match, the Center of curvature of the Hindle need to
match with the focus of the Hyperbola under test. So if the Hindle is bigger
we can put it far away as long as this condition is met and it still
illuminates the whole secondary. But in my case the biggest distance I can
put the Hindle I still have to bring my 16" F3 to F2, too much glass to
remove!

Jonathan

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