Re: [ATM] Two mirrors small size difference

["Paul Bradley" <paul@paul-bradley.com>]

Bob,

That's what I was thinking. When I said they were close I mean that they
are within 0.5% in focal length when their individual sagitta and diameters
are used to calculate the focal length.

I was more concerned that the smaller mirror would not grind correctly in 
some
way, but once I thought about it properly I realised 2 spherical sections 
would be in
contact no matter the size - the curvature is the same everywhere. Strange 
how it
sometimes takes confirmation of something before you can think straight 
about it. ho hum.

Back to the grind.

Thanks.

Paul

----- Original Message ----- 
From: "Bob May" <bobmay@nethere.com>
To: <atm@atmlist.net>
Sent: Tuesday, October 11, 2005 7:24 PM
Subject: Re: [ATM] Two mirrors small size difference


> When you think about how you mreasure saggita, the smaller mirror
> should have a smaller sag. if you measure with a straightedge
> across the whole mirror.  One of the ingredients of the sag.
> calculations is the radius of the measurement circle and since
> you have two different diameters, you'll get two different sag.
> measurements!
> Bob May
> bobmay at nethere.com
> http: slash /nav.to slash bobmay
> http: slash /bobmay dot astronomy.net
> Addresses have been munged up to keep spammers from bothering me.
> replace the obvious words with the proper character.
> Thank you for your understanding!
>
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