Re: concave mirror with hole

"redbelly" <redbelly98@xxxxxxxxx> wrote in message
news:1157642218.712574.80650@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

JoeBloe wrote:
On 6 Sep 2006 14:35:52 -0700, "redbelly" <redbelly98@xxxxxxxxx> Gave
us:

I doubt it will matter. You're not concerned with forming an image,
you're just collecting as much power as you can on a detector.

Which, to be done properly, REQUIRES a good quality mirror. First
and foremost. It IS "forming an image".

Okay, so it should have said "not forming a **high-resolution** image".

An IR tube "forms an image" of the target onto a 2mm spot inside the
detector transducer.

It IS simple optics, no matter how you want to attempt to simplify
it. No image, no energy is "seen". PERIOD.

It's simple, no matter how I attempt to simply it??? That doesn't even
make sense.

Well from my recent experience it does need to form an image,
not necesarily an undistorted one of course,
but certainly a relativly small but clearly visible and relativly bright
image in the center anyway,
wich means it needs to at least be very shiny, and quite close to the right
shape.
the metal mirror I tried,
wich I later found a good way to test by puting a simple led torch some
distance away from it,
forms a clearly visible quite bright image but a rather large one, so most
of the light isnt captured by the 1mm^2 detector.
I just did it with a piece of .15 mm *** steel and a ball pein hammer and
a flat metal surface,
fortunatly I do have a little bit of skill necesary to do it that way.
If I made a wooden dolly of the right shape im sure I could get it close
enough.

However I think any DIY method to make one, although possible, would need
quite a bit of time to make it good enough.
I picked up a CD to play with but actually they dont reflect a great deal of
light, they are partly transparent and also much of the light is difracted.

The lamp mirror im using now forms an image wich is quite bright in the
center 1mm part of it, although its certainly not a just a well defined dot,
I think the much shorter focul length is a big advantage.

It works enough to prove the signal is from the demodulated reflected light
rather than crosstalk,
as moving the target through 75mm (at about 200mm away) clearly cuases 180'
phase change in the signal (at modulation = 1ghz).
now I need to try and get it to work at 2ghz.

In other places I have seen telescope guys make their own mirrors using 2
quite large bits of glass rubbed together with grinding paste,
then silvered in a home made alu sputtering chamber !

Colin =^.^=


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