Re: [ATM] Houghton Triplet Corrector

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

Ukyo Chen wrote:

>Hi John and other ATMers,
>
>You can download the US Patent 2,350,112 which is Houghton's design.
>The website for dowload is http://www.uspto.gov/
>Or you can visit my website, I had put the pic to there already: 
>http://spaces.msn.com/members/ukyochen888/
>
>Or if you want, please send a mail to me and I will attach the document to 
>you for free.
>
>Best Regards,
>Ukyo Chen
>
>  
>
Re: Figure 2 of the patent; the triplet corrector with the same glass 
for all three elements

OK, I can understand why the author chose a high index glass (something 
near N-SF6)...  the
curvatures are shallower. But why such a low Abbe number --  doesn't 
that just invite higher
variation with wavelength?
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