Hi,

I'm a 3rd year physics undergraduate. I have been assigned an experiment to
do called Optical Beams. The notes say to use a ray-tracing program called
Beam Three from Steller Software. I've had a look at this and it seems
ancient and has an awful interface. I would like to use POV-Ray instead,
but I'm not sure if it's as 'scientifically-capable' as Beam Three. I've
pasted in below what I've been asked to do. I'd be grateful if anyone could
give a quick response to say whether the general ideas are feasable to do
within POV-Ray.

---

Suggestions for experiments
Aberration from a single lens

    *
    * Astigmatism is the variation of the focal length of a lens as it is
tilted away from axis. Use a thin lens (for instance 2 cm diameter and a
nominal focal length of 1 m) and observe how the focal length varies with
the tilt angle. Plot focal length vs. angle (in Excel) and compare with
your theoretical expectation.
      Spherical aberration is the variation of the focal length for rays
travelling parallel to the axis of a lens but crossing the surface at
different distances from the centre. Choose lenses of different shapes
(concavo-convex, planoconvex, double-convex) but the same diameter and
focal length (for instance 2 cm and 10 cm) and find the variation in focal
length across the surface of the lens. Plot this variation as a function of
the shape parameter q for the lens defined as



      where R1 and R2 are the radii of curvature of the front and back
surfaces of the lens respectively.

    *
    * Coma is the variation in distance from the lens axis to the focus
(image height) for rays travelling at an angle to the axis and crossing the
surface at different distances from the centre. Choose lenses of different
shapes but the same diameter and focal length and find the variation in
image height across the surface. Plot this variation as a function of the
shape parameter q.
      Chromatic aberration is the variation in focal length due to the
dispersion of the lens material. It can be largely compensated by cementing
together two lenses made of different materials. Design an achromatic
doublet (use for instance BK7 and SK16 glass) with a focal length of 10 cm.
Choose parameters that also minimise spherical aberration and coma.

Beam expander

Design a telescope that expands a beam by a factor of five. Try two convex
lenses as well as a convex and a concave. Choose the shape of the lenses to
minimise spherical aberration.
Other optical instruments

Use the ray-tracing programme to design other optical instruments such as:

    *
    * A microscope objective
    * A camera lens (telephoto)
    * Reflecting telescope (try an aspheric mirror to reduce aberration)
    * An eye with glasses or a contact lens
    * The Hubble telescope with correction lens
      Anything else you can think of

Post a reply to this message

AndyW wrote:

> Hi,
> 
> I'm a 3rd year physics undergraduate. I have been assigned an experiment to
> do called Optical Beams. The notes say to use a ray-tracing program called
> Beam Three from Steller Software. I've had a look at this and it seems
> ancient and has an awful interface. I would like to use POV-Ray instead,
> but I'm not sure if it's as 'scientifically-capable' as Beam Three. I've
> pasted in below what I've been asked to do. I'd be grateful if anyone could
> give a quick response to say whether the general ideas are feasable to do
> within POV-Ray.

looking at beam three, it appears to me that this is a completely 
different animal from POV-Ray. I would recommend you use it over a 
program like POV-Ray, simply because it was designed to model lenses.

While some of the experiments you listed could be visualised with 
POV-Ray, I don't think the effects would be 100% measurable, or 
accurate. Also, the means to get the light to show up involves photons 
and media, which will cause even the simplest scenes to render in hours, 
possibly days.

-- 
~Mike

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