Re: concave mirror with hole

"Don Foreman" <dforeman@xxxxxxxxxxxxxxxxxxxx> wrote in message
news:t52qf217c09macdpo29a3u0gru4vqnntuc@xxxxxxxxxx
On Mon, 04 Sep 2006 21:06:59 +0200, Rene Tschaggelar <none@xxxxxxxx>
wrote:

colin wrote:

Hi,
Anyone know where I can get hold of a mirror with a hole in it ?
Its for my lidar,
the idea is for the laser to shine through the hole in the center of
the
mirror,
the returned light from the target is then reflected via the mirror
onto the
PD,
thus ensuring ensuring the axis of detection is the same as the beam of
the
laser.

Diameter needs to be about 30->50mm,
hole diameter about 5mm,
focul length about 30->50mm
and fairly cheep.
I could drill a hole in a metal mirror but dont realy want to try it
with
glass.

Oh and the reflected light from the mirror will be at an angle of about
20'
from the incoming light,
does this mean the mirror needs to be a different shape for optimum
focus or
will it make little difference ?

Many people drill holes into a glass mirror from
the backside. You won't get a 30-50mm mirror with
a focal lentgh of 30-50mm. this is the domain
of lenses.

Rene

The diameter is presumably for capture area. Given your offset and
short focal length, the way to do this is probably to use an
offset-fed paraboloidal section somewhat like a DirecTV dish.

Possibly suitable aluminum paraboloidal reflectors are available from
Carley Lamp.

http://www.carleylamps.com/reflectors.htm

You can machine away the parts you don't need with the tools of your
choice -- laser, waterjet, plasma cutter, milling machine,
jeweller's saw, hack saw, whatever turns yer crank.

Interesting choice of weapons, maybe if I leave the laser on for long enough
it will cut its own hole.

Gives me an idea tho, to use a plastic torch lense wich I can easily cut a
section off to the side and melt a new hole.

thanks
Colin =^.^=


.

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