Re: [ATM] Five restricted eyepieces

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

Richard F.L.R. Snashall wrote:
   > It struck me that, in general, eyepiece designs do not look like
   > they are designed for individuals who wear glasses.  Some of the
   > ERs! (Do people who wear glasses actually buy eyepieces with
   > focal lengths under a half-inch?)

Ellen Mackenzie suggested that I look into the possibility of
inserting a negative achromat into the convergent beam.  Indeed,
adding such an achromat well in front of the eyepiece seems to
be able to not only gain in ER but also improve performance:

            R           t          G         D
           inf        2.0       N-SF1       22.4
          20.749      8.6       N-LAF34     22.4
         -20.749      0.1
          20.749      5.3       N-BK7       22.4   Melles Griot LPX083
           inf        0.1
          19.239      8.2       N-BK7       21.0   Melles Griot LDX027
         -19.239      2.0       N-SF1       21.0
          19.239      2.696
                     59.244                        original focal plane
         -75.5287     3.2       N-SF5       18.0   Spindler & Hoyer
         -24.28743    1.5       N-BK7       18.0     325221
          30.28743  -28.3809

At first, I thought the negative achromat would act as a Barlow, but
actually this combination has an EFL of 6.154 mm, quite a bit shorter
than the original 13.6 mm.  Even better, the ER is now about 13.4 mm,
or 217.2% of the EFL!  As I mentioned, performance is also improved,
so that the Strehl ratio is actually over 0.033 for the whole field.

-- 

Rick S.

http://users.rcn.com/rflrs




_______________________________________________
ATM mailing list http://www.atmlist.net/