Thermal Imaging Camera?

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On Wed, 10 Dec 2003 15:27:57 -0000, "David Hearn"

They probably use infra-red LEDs internally for film sensing
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Mike Harrison wrote:

They do indeed. Some of the higher range ones use other methods, but certainly mine uses IR internally for film speed detection, I believe.
Velvet
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David Hearn wrote:

Foucussing probably. You need a fairly 'manual' camera.

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The Natural Philosopher wrote:

Many manual lenses have an IR focus mark slightly offset from the main focus mark. The intention is you focus visually as normal - but then shift the focus from the normal position to the IR position marked on the lense to allow for the slight difference in refractive power at that wavelength.
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Phil wrote:

Again, like the CCDs this won't give you long IR, so will not be of any use for detecting IR emitted by objects at room temperature.
Think about it - if it did, how would you stop the film from going off the minute it's produced?
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Grunff


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On Wed, 10 Dec 2003 15:33:08 +0000, Grunff wrote:

By keeping it cold.
Might be a tad tricky to load though.
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Grunff wrote:

This did bother me a lot but as the Kodak example is a picture of a tree which shirley must be colder than a house I assumed that some sort of black magic must be happening. Film you keep in the freezer? Cameras you keep in the fridge? Err ...
Phil
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Phil wrote:

But as soon as any part of the camer reached room temperature, including the sutter or even the lens, your film is toast.
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Phil wrote:

Unrelated to IR specifically - but films do keep better colour accuracy if you keep them cool. This is more true of the "pro" films rather than the more consumer oriented versions.
In our local camera shop they have a display fridge for all of the better films.
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Grunff wrote:

It does. You tend to keep it in a fridge.
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The Natural Philosopher wrote:

Are you saying there's IR film sensitive at 3um+ ?
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Grunff wrote:

No, but I seriously doubt you have to go to that lengh to get a meaningful image.

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The Natural Philosopher wrote:

You gone and done it now - you made me think about it.
Gut feeling says you'll get next to nothing under a micron at 300K.
This is backed up by this graph: <http://www.egglescliffe.org.uk/physics/astronomy/blackbody/bbody.html
I dusted off the old calculator, and calculated the emitted power per square metre (black body) using the Planck energy distribution formula.
For 300k and 1um, and it came to ~6x10-7 W/m^2. I don't reckon any film has the sensitivity to pick that up out of the overall background. I may be wrong, but I remain to be convinced.
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Grunff wrote:

Well, I have seen a few IR photos, and they definitely seem to show people and faces as rather bright.
Probably the only thing to do is to try it.
Film can pick up just one photon you know. It is sensitive...the point being does the near infra red actually give any meaningful correlation with heat? I also vaguely remember flash guns usd in dark places coverd with IR filters.
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Even if it was, it wouldn't be very useful in a camera, the glass in the lens would block the IR .... I believe that's how windows work.
Special gallium something or other lenses are required which are mega expensive - one of the main costs of a thermal imager.
IR film *mainly* detects the shorter (near visible) wavelength radiation that is mainly reflected - not emitted - from objects (unless they are very hot).
Dave
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I think the old Land Pyrometer used a germanium lens. A reflector focussing system can have a much wider optical bandwidth than lenses.
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Tony Williams.

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Dave Gibson wrote:
In the past I have done work on avionics spec thermal imaging kit (i.e. the good stuff - not just the images they let you see on telly!)

Looking round the lab with a steerable thermal imager with built in thermal telescope was "educational"!
Needless to say, you could get into serious trouble if any of the ladies in the lab even thought you were pointing it in their direction!
(although this is where video autotrackers have uses - you can be well away from the controls and leave it to follow the "hot body").

That's right, machined from germanium, totally opaque to normal light. The telescope fitted to the setup I was using cost about 100K on its own. Ordinary glass looks black, opaque and a little reflective on a thermal image - no use at all for lenses.

As you say, IR film is a world away from real thermal imaging. The best high resolution kit, is sensitive enough to see the thermal impression of foot prints left after someone has just walked normally over a bit of floor (in shoes)!
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John.

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When I worked on a contract in Germany once, a germanium lens which had been ordered arrived in QA
They measured it - yes it was 24mm in diameter - PASS
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Good thing you weren't anywhere else - a californium lens for instance wouldn't have worked.
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Hey, I missed that one, didn't I
I must be growing old
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