Re: [ATM] to make an eyepiece

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

David Williams wrote:
> Hello
> 
> I just wondered about the Plossl or Symmetric design of eyepiece.  Can I use the achromat doublet that I found on this page:
> 
> http://www.surplusshed.com/pages/item/l2076.html
> 
> where it says that it is a MELLES GRIOT PRECISION ACHROMAT, 31.5MM DIA X 80MM FL              I could use two of them and then turn them so that their curved sides are facing each other and them space them so that they're almost touching and then bond them inside of an eyepiece barrel.

So far, the prescription for this has me a bit perplexed.  It looked,
at first, as if they chose SK11 and SF8 glasses as the Abbe numbers
are close to a 2-to-1 ratio.  However, when advantage of that is
taken, the minimum focus when OSC is nulled is at 603.3 nm.  This
prescription has the minimum focus at about 518 nm.

It "looks" as if they simply grabbed the glasses, picked a minimum
focal length wavelength, calculated the initial values, and then
optimized only the last surface.  !%&^(^$%!

-- 

Rick S.

http://users.rcn.com/rflrs

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