Re: [ATM] A Null Test

["Richard F.L.R. Snashall" <rflrs@rcn.com>]

Ric Rokosz wrote:
>>         c) 25-25.4 mm diameter variable f.l. (c. 100
>> to 200 mm) biconvex
>>     
>
> I find your work on the these null lenses very
> interesting and do appreciated the work involved.I do
> have one concern and that is the use of biconvex
> lenses.If one uses a vernier caliper to set the
> spacing you need large jaws to reach down to the apex
> of the lens and this can introduces angle error and
> the resulted spacing error - not much of course but
> how tolerant can the spacing be? Using plano-convex
> lenses makes things a lot easier.
>   
 From this, I'm getting the impression you are thinking of a
rail instead of some form of double drawtube.  Correct?
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