ATM Tri-space Refractor Prescription

[Roger Ceragioli <rogerc@dakotacom.net>]

Here is the prescription for an 8" f/15 tri-space refractor which I
designed last week.  Some people on the list had asked for this information. 

Aperture: 8" (all dimensions in inches)

r1 = 73.015          t(hickness)1 = 0.75          BK7          conic = 0.0816
r2 = -42.477         a(irgap)1    = 0.0

r3 = -42.985         t2           = 0.5           F2
r4 = -175.854        a2           = 80.0

r5 = -43.637         t3           = 0.5           B58-53
r6 = -2.399          t4           = 0.2           KZFSN2
r7 = 5.187           t5           = 0.5           BAK1
r8 = -54.539         a3           = 38.993

Notes:
1) The zero-thickness airgap between the two elements of the objective was
a design mistake of mine.  Some small finite thickness should be used instead.
2) I slightly aspherized r1 in order to improve performance.  This would
happen automatically, if you autocollimated the system to do the final
figuring and worked r1 of the objective.
3) A3 is just the back focal length.
4) The design wavelengths used to generate this prescription on ZEMAX were
d (.586 um), F (.486 um), and C (.656).  The indices of refraction are as
follows:

           F         d         C
BK7       1.52238   1.51680   1.51432
F2        1.63208   1.62004   1.61503
B58-53    1.56495   1.55751   1.55434
KzFSN2    1.56552   1.55836   1.55521
BAK1      1.57943   1.57250   1.56949

I have been unable to find a Schott or Ohara equivalent to Corning B58-53.
The closest Schott glass seems to be BaLF 5.  I'm not sure how well this
glass will work as a substitute.  At present I have submitted a quote to
Corning for their glass in a 4" size, but have not yet received a reply.

Roger Ceragioli