[Raytrace] A real world application

[Peter John Smith]

Re the Pressmann-Camichel Peter Chen would like.

I once looked at the Pressmann-Camichel and left this design with the
feeling that it had little to offer.

One thing that I discovered was that for a pure conic to work on the
secondary, the image position was very limited.

Below is a design that I did but I must still echo Michael Peck's thoughts
that its nearly undoable, even for pros. as the conic on the sec is very
extreme.  And of course, it has almost no useable field outside the paraxial
zone.

I think the position of the image in this example (just in front of the
primary) may be acceptable if a small CCD is used.

=========================================

Effective Focal Length  :        2130.686 (in air)

SURFACE DATA SUMMARY:

Surf     Type         Radius      Thickness                Glass
Diameter          Conic
 OBJ STANDARD       Infinity       Infinity
0              0
 STO STANDARD       -1950.72      -682.3888               MIRROR
508.029              0
   2 STANDARD      -1080.612            640               MIRROR
151.9112        13.6537
 IMA STANDARD       Infinity
3.998507              0

I see that the image is for a field of 0.05 degrees but the results off axis
are essentially unuseable.

========================================

In general, I have found that making a success of a spherical primary is
very difficult without either very wide or very complex corrective optics.

Here is a Cass type design using all spherical surfaces which is of some
interest.  It is a 1 m scope, uses a mangin secondary which is an
equiconcave "lens" before it is silvered on one side so it can be tested as
two convex surfaces, then a 200 mm diam corrective meniscus lens about half
way back to the primary, finally another small concave corrective lens 250
mm in front of the image.   I think it will just fit into OSLO LT.

All glass is BK7 and as stated all surfaces are spherical.  Although the
field is 60 mm across, it is too curved for flat film of this size.

I think the design quite interesting, especially as it uses all BK7  but its
certainly not a simple ATM scope, not entirely sensible.  Which illustrates
what I said about Spherical Primaries.  To correct them without large
diameter surfaces gets messy.  If anyone has interesting solutions using sub
diameter correctors I am all ears.

Maybe someone might like to examine or even build on this design.

==================================

System/Prescription Data

File : C:\usr\lenses\ByDate\01\01July\SphericalPrimary\Mangin\a4.ZMX

Effective Focal Length  :            7000 (in air)

Image Space F/#         :               7

Fields          : 4
Field Type: Angle in degrees
#        X-Value        Y-Value         Weight
 1       0.000000       0.000000       1.000000
 2       0.000000       0.080000       1.000000
 3       0.000000       0.160000       1.000000
 4       0.000000       0.250000       1.000000


Wavelengths     : 5
Units: Microns
#          Value         Weight
 1       0.470000       0.091000
 2       0.510000       0.503000
 3       0.555000       1.000000
 4       0.610000       0.503000
 5       0.650000       0.107000

SURFACE DATA SUMMARY:

Surf     Type         Radius      Thickness                Glass
Diameter          Conic
 OBJ STANDARD       Infinity       Infinity
0              0
 STO STANDARD          -6600      -2199.759               MIRROR
1000.166              0
   2 STANDARD        6727.12            -15                  BK7
353.498              0
   3 STANDARD       -6727.12             15               MIRROR
350.067              0
   4 STANDARD        6727.12            850
348.6887              0
   5 STANDARD       579.9506             22                  BK7
279.2098              0
   6 STANDARD       2133.934       765.1582
277.1144              0
   7 STANDARD       265.5515              8                  BK7
71.22697              0
   8 STANDARD        96.5718            250
68.05869              0
 IMA STANDARD       495.3182
61.73862              0

==============================================

Surface 2, 3, and 4 represents the Mangin secondary.

This can be a real source of programming errors.

In Zemax, it is not necessary to specify that the glass type between surf 3
and 4 is actually a return path through the BK7.  I think other raytracers
may have a different protocol so beware.

If you have never entered a design like this it may be an interesting
exercise.

Have fun

Peter Smith.