Re: [ATM] Luri-Houghton prescriptions.

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

Bob May wrote:

>
>Supprizingly, turning the curvature convex does hurt the spot
>size more!  I haven't traced Ykyo's design yet but it does look
>good in Oslo.
>
Actually, you might be able to turn it slightly convex to achieve
the same advantage achieved via index/f# selection, e.g.:

Surf      Radius      Thickness      Glass      Diameter
 OBJ    Infinity       Infinity                        0
 STO    Infinity     -0.1642415                     12.5
   2         119           0.78      N-BK7            13
   3      -457.2            0.2                       13
   4      -90.53          0.546      N-BK7            13
   5       -2232           50.5                       13
   6        -119          -48.5     MIRROR         13.75
   7    Infinity      -10.95753                 3.963898
 IM    -170.8387                                 1.70039

You lose about 0.004" of central thickness, but gain the equality
constraint.  The sag of the last surface ends up about 0.0095"
at the given diameter.
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