Re: 2" 90° Apparent Field Eyepieces Announced

From: brian (brianc1959_at_aol.com)
Date: 07/02/04 

Date: 2 Jul 2004 07:07:53 -0700

shneor@my-deja.com (Shneor Sherman) wrote in message news:<9dedb1fb.0406300643.2e10efd6@posting.google.com>...
> jonisaacs@aol.com (Jon Isaacs) wrote in message news:<20040629175818.11708.00000633@mb-m11.aol.com>...
> > >My experience with Burgess has been excellent value for the money. But
> > >I do wonder about the optical characteristics of this eyepiece.
> > >
> > >Clear skies,
> > >Shneor Sherman
> >
> > Probably best to take the wait and see attitude if something isn't currently
> > yet available. Burgess Optical has been somewhat optimistic in the past about
> > delivery dates...
> >
> > Jon
>
> Here's some more info from Bill Burgess: It's a 7-element design, all
> ED glass,"broadband multicoatings on all air-to-glass surfaces", and
> pinpoint stars to the edge down to f/3.5. Availability is at least 60
> days out.
>
> The part about pinpoint stars to the edge of a 90° apparent field 29mm
> eyepiece sounds very attractive. Maybe some of our eyepiece design
> mavens can tell us why this is either impossible or comes at the price
> of field curvature, loss of contrast or some other desirable optical
> characteristic. Or not.
>
> Clear skies,
> Shneor Sherman

Don Dilworth demonstrated that its possible to build a 90deg. eyepiece
with extraordinary performance. See U.S. Patent 4,720,183. The
designs published in this patent are among the highest performance
eyepieces I've ever seen. Much better than even the published Nagler
designs. No ED or high-index lanthanum type glasses are needed. The
only drawback is size. A 29mm focal length would have some elements
as large as 4" in diameter. Below is the patent prescription for a
15.9mm Dilworth:

Surf Radius Thickness Glass Diameter
 OBJ Infinity Infinity 0
 STO Infinity 16.367 3.984463
   2 -46.13459 1.294 1.805180,25.430 34
   3 59.64817 12.152 1.638540,55.420 39
   4 -25.6419 0.4099999 39
   5 104.509 14.0534 1.620410,60.320 60
   6 -57.40218 24.826 60
   7 50.58608 12.4375 1.620410,60.320 62
   8 4353.534 0.4099999 62
   9 23.4904 10.75047 1.620410,60.320 45.2
  10 26.7368 11.6589 40
  11 -83.8454 3.57986 1.620040,36.370 40
  12 23.38768 14.06033 32
  13 33.9786 5.868849 1.846660,23.830 33
  14 221.1201 4.122499 33
  15 -46.2614 3.39373 1.539960,59.710 33
  16 56.31179 -27.43597 33
 IMA Infinity 28.58338

Brian
www.caldwellphotographic.com

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