Re: [ATM] Sphereometer accuracy

["Jerry" <wa4guu@verizon.net>]

I took a look at Nanotechsys.com.
Verrrrry interesting.  And so close to Stellafane.

Jerry



-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Jeff Lowe
Sent: Thursday, February 23, 2006 8:22 AM
To: atm@atmlist.net
Subject: Re: [ATM] Sphereometer accuracy

From: "Jerry" <wa4guu@verizon.net>
 > Message-ID: <002e01c637fd$37a0b390$0100a8c0@D85SJB21>
 >
 >If I am not mistaken....
 >
 > You would only have to add or subtract (depending concave
 > or convex) half the diameter of the balls to/from a radius
 > calculated using the centers of the balls as the locations
 > of the feet.

Exactly. The radius used in the spherometer equation is the radius at 
the center of the balls. The radius of the ball feet is then a power 
correction that is subsequently added to the mirror radius in the case 
of a concave optic, or subtracted in the case of a convex. Larger balls 
are generally preferred as they reduce the contact pressure and are less 
likely to damage the surface (ref:Hertz). In addition, due to the larger 
contact patch, they are less sensitive to minute surface irregularities 
present during the rough grinding stage.

jeff


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