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From: rats@ihlpm.att.com (David Woo)
Newsgroups: sci.military
Subject: Re: night-vision glasses
Message-ID: <1991Feb4.055309.17237@cbnews.att.com>
Date: 4 Feb 91 05:53:09 GMT
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From: rats@ihlpm.att.com (David Woo)

In <1991Jan27.110402.28050@cbnews.att.com> gregg states:

|  On CNN a few nights ago, there were video images taken through
|what they called a infrared "night vision" camera. Can anyone
|tell me the specifications (or provide references) for such a
|device? In particular, I am looking for the ambient lighting
|conditions, the distance range (which is probably a factor of the
|size of the aperture), the sensitivity, the physical size, and
|the cost.  

Your best bet is to contact the manufacturers and distributors,
such as VARO, ITT, LITTON, etc. You can usually determine if they
are using an external image intensifier device on a conventional
camera if you see a "T" shaped reticule somewhere on the screen.

|  Also, are hand-held units ever used? I've seen TV shows
|(possibly fictional) in which these were worn by a person, and
|looked like a large pair of binoculars. Also, are monocular
|versions around?

Yes to all of the above. Some of the binocular devices utilise a
single image intensifier tube in order to save money. The U.S. military
I believe basically uses a rifle model, a Crew Served Weaponsight model,
(Both which use CAT optics) and night vision goggles.

|  Do these devices combine different electronmagnetic spectra to
|produce the final image? That is, do they see heat and light, or
|just heat? Why is it that we can't see through clouds of petro
|products with these?

I think you are a little confused here. The current "night vision"
devices are IMAGE INTENSIFIER devices, which depend on utilising a
photocathode. This means that they are optimised for detection in
the electromagnetic spectrum that dominates the night sky - the near-IR
region plus some of the visible light region. They are not thermal
devices at all. The output of these devices is usually in the form
of a P-20 or similar phosphor screen (green color). That is why you
don't see true color images from a "night vision" camera. I have seen
pictures of a color image intensification device that tried to generate
a color picture through the use of prisms that separated the spectrum
before entering an array of II tubes, which subsequently combined
the outputs to give a non-monchrome image.

The main problem with combining images from different sources besides
from size is that every system has their own idiosynchronous distortions;
for an image intensifier tube, it is the electron optics for focusing
the image, thou proximity focusing as used on night vision goggles
does a reasonably good job.

Thermal imaging handheld weaponsights have a long way to go, though I
have seen pictures of MAGNAVOX units on top of M-16 rifles. Perhaps
these use pyroelectric vidicons?

Note, for example, that the APACHE helicopter TAD/PVNS carries both
a FLIR unit AND a LLL camera, and the system, as far as I know, doesn't
combine the images of both together.

|--gregg (tracton@godot.radonc.unc.edu)