Re: [ATM] Sphereometer accuracy

[hermit <hermit@outofoptions.org>]

Since it is easier to measer the ROC of a finished mirror, I just worked 
backwards to get the specs for  a spherometer that was given to me.

Ken

Dominic-Luc Webb wrote:

>-------------------
>  
>
>>In reading the recent posts about sphereometers, it occured 
>>to me that when using balls for feet, the actual spacing 
>>between the feet will vary with the depth of the curve being 
>>measured; the spacing gets wider with concave surfaces, and 
>>narrower with convex ones. 
>>    
>>
>
>Exactly my point for years now. If someone REALLY needs such 
>precision, then maybe measuring the actual ROC with reflected 
>light source using a micrometer attached to a piece of paper at 
>ROC would be more appropriate. There are very few of us that 
>really need the ROC to be this exact using a spherometer.
>
>More to the point from my observations, some newbies 
>get depth easily within useful specs (goal is F/5.0, and 
>they get F/5.0 +/- negligible error), but are not getting 
>spheres right from the early stages of grinding.
>
>Dominic-Luc Webb
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>  
>

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