[Raytrace] Where To Start?

[John D. Upton]

Ken,

At 09:51 PM 12/6/2001 -0500, Ken Lowther wrote:
>For many of us, a simple file to look at in a program might help.  Maybe
>pick a program and look at the file and do simple modifications.  A
>simple lens might be a good starting place.  Followed by a reflector.

     Perhaps a couple of text prescriptions from OSLO will help illustrate 
the (typical?) data entry formats.

     This is the text printout of an OSLO design for a simple double convex 
lens made of Schott BK7 glass.

*LENS DATA
Simple Double Convex Lens
  SRF      RADIUS      THICKNESS   APERTURE RADIUS       GLASS  SPE
  OBJ       --        1.0000e+20    1.0000e+14             AIR
  AST    10.000000      0.250000      1.000000 AS          BK7 C
   2    -20.000000     12.826432 S    0.991482 S           AIR
  IMS       --            --        1.2937e-05 S

     The lines labeled AST and 2 describe the lens.  (The AST just means 
that the aperture stop for the lens is at the first surface.)  Remember 
that it takes two lines (surfaces) to fully describe a lens.  The left side 
has a ROC of 10.0" and the right side 20.0"  Note that the right side's 
curvature is negative since it is convex and the COC must be to the left of 
the surface.  The thickness of the lens is shown on the AST line.  It is 
0.25" thick.  The thickness shown on line 2 is the "thickness of the air 
between the right surface of the lens and the image plane -- in other words 
the focal length is 12.826".

     Now, here is an example for a concave spherical mirror with a ROC of 30".

*LENS DATA
Simple Spherical Mirror
  SRF      RADIUS      THICKNESS   APERTURE RADIUS       GLASS  SPE
  OBJ       --        1.0000e+20    1.0000e+14             AIR
  AST   -30.000000    -15.000000 S    3.000000 AS   REFL_HATCH
  IMS       --            --        1.5000e-05 S

     In this case, the AST line shows the mirror.  The ROC is negative 
since the COC is to the left of the mirror's surface.  The thickness is 
again the focal length or the thickness of air between the mirror's surface 
and the image plane.  The focal length is negative because the light has 
reflected off the mirror and is now travelling right to left.

     Do these two examples help illustrate the rules or conventions in the 
previous note?


John D. Upton
Georgetown, TX
<http://www.atm-workshop.com/>     "The ATM's Workshop"
<http://members.aol.com/RonWin20/> "Ronchi For Windows Home Page"