Don Foreman wrote:
On 16 Nov 2004 23:45:27 GMT, Ian Stirling
wrote:

The reteroreflector lets you shrink the size, while retaining beam
quality.

True if "beam quality" means maximum collimation for long "throw",

It does.

The reflector will be movable, so that in combination with altered
reflectivity (either white or shiny, I'm unsure which is best) of the
inside, you can go from various different beam shapes, from a tight
beam, to a wide flood.

It was the only possible solution for reterofitting a mini-maglite solitare.

With a conventional parabola, you lose a lot of the light out the front,
with most designs, meaning you don't get a nice sharp beam, but a lot of
light goes round the edges.

So an unconventional parabola would be better? What sort of
unconventional parabola might that be? Unconventional focal length
perhaps. The trick in a retro is to match the reflector to the
feed's radiation pattern so the feed port doesn't block the beam.

Err, no.
I was referring to the fact that a parabola with a light source at the
focus is conventional for lights.
You need to go to a very large parabola to reduce the amount of light
going to the sides.
If you put a lens in front of the parabola, then you can fix that, but
it's then got to be some other shape.

I played with this using the radiation pattern of a white Luxeon
side-shooter emitter with the constraint of reflecting nearly all
emitted light in the beam while blocking nearly none with the emitter
in the retro path. Math model. Found a minimum exit aperture and
focal length of truncated paraboloid of revolution to make it so.

The side-shooter isn't really ideal, because you get (AIUI) two
different places that the light comes from, the front reflector, and
the direct radiation. This makes focusing a problem.

You're surely well past my primitive level of understanding, but I
found it fun to explore. Question for you, pls: how will you
make and then reflectorize your reflectors?

Polished hardened steel former, silver sheet + big hammer.

2cm^2 of silver sheet is cheap.