On Wed, 21 Aug 2013 19:25:19 +0800, Mike B someone@noplace wrote:

This is for a searchlight application where the light source shines backwards
into the reflector which then reflects the light forwards producing a narrow
beam.
The reflector needs to be about 2 to 3 inches in diameter with a focal point
about 2 to 3 inches in front.

Presumably this was possible in the days before CNC machinery, so how did they
do it?

The following picture gives you an idea of the size, curvature and surface
finish required
http://www.motherearthnews.com/~/med...21_9386858.gif
It's actually a "solar fire starter" so the light is traveling in the opposite
direction, but the optical path is the same.


Mike

Every "solar fire starter" Ive owned was oval, not round. And they
indeed did work pretty well. They were not made out of stainless
steel, but chrome plated sheet steel and over time..everyone of them
started to rust until the ability to gather enough sun became
compromised.


"There are no leftists in mainstream American politics.

Just two right wing parties, one hard right and one softer."
Christopher A. Lee, 8/18/2013