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Infra Red Remote Controls


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hilldweller

Saw a little technical tip on the t'internet the other day and thought I'd share it with you.

If you think your T V, DVD, or whatever, infra red remote control isn't working, it's no good looking at the transmitting LED on the end to see if it's working because your eyes won't see it.

Grab your digital camera however and switch it on, point the remote towards the lens and look at the camera display while you press the remote buttons and you'll see the LED light up in a blue/purple light if it's working.

HD

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Saw a little technical tip on the t'internet the other day and thought I'd share it with you.

If you think your T V, DVD, or whatever, infra red remote control isn't working, it's no good looking at the transmitting LED on the end to see if it's working because your eyes won't see it.

Grab your digital camera however and switch it on, point the remote towards the lens and look at the camera display while you press the remote buttons and you'll see the LED light up in a blue/purple light if it's working.

HD

So, why would an ordinary digital camera, used to record images created using the visible light part of the spectrum be made to render invisible ir radiation as a blue coloured light?

Infra red is actually absorbed by glass so big, complex, multi element lenses tend not to let it through, - although simple lenses will and it does depend on the frequency of the ir radiation,

Further to this, lenses refract different frequencies by different amounts and so brings them to a different focal point. In ordinary photography with light this problem is called chromatic abberation and gives rainbow like edges in severe cases. In ir photography it means that if the visual image is in sharp focus the ir one isn't and so lenses intended for ir photography usually have a seperate or modified focusing scale.

However, I still can't see why it would be necessary for an ordinary digital camera to "see" infra red at all.

It may just be "what happens" but I can see that in some situations it could create problems by appearing on photos when it shouldn't be there.

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hilldweller

So, why would an ordinary digital camera, used to record images created using the visible light part of the spectrum be made to render invisible ir radiation as a blue coloured light?

Infra red is actually absorbed by glass so big, complex, multi element lenses tend not to let it through, - although simple lenses will and it does depend on the frequency of the ir radiation,

Further to this, lenses refract different frequencies by different amounts and so brings them to a different focal point. In ordinary photography with light this problem is called chromatic abberation and gives rainbow like edges in severe cases. In ir photography it means that if the visual image is in sharp focus the ir one isn't and so lenses intended for ir photography usually have a seperate or modified focusing scale.

However, I still can't see why it would be necessary for an ordinary digital camera to "see" infra red at all.

It may just be "what happens" but I can see that in some situations it could create problems by appearing on photos when it shouldn't be there.

According to Wikiwhotsits, digital cameras are inherently sensitive to infra red light and in order not to mess up focus-ing or colour rendering they utilise a IR filter in front of the sensor.

I suppose it might be the presence of the filter that gives the blue/violet effect.

When I worked in the steel industry we made extensive use of CCTV. One application was in the billet mill where a camera was located on the opposite side of the big roughing mills 'so the operator could work the manipulators to send the 2.5 tonne orange hot billets back to his side of the mill as it was passed back and forth to reduce it's cross section.

In those days the cameras used "Vidicons", a sort of reverse of a cathode ray tube, where the image was focussed on the target in the end of the tube and scanned by an electron beam. The beam current changed according to the image brightness and thus gave a signal.

Unfortunately ordinary Vidicons were very sensitive to IR radiation and the image was ruined by flare from the very hot billets.

The solution was to use special ultra violet sensitive Vidicons and flood the area with UV light from large mercury vapour lamps.

These lamps used bare quartz tubes and you had to be very careful not to stare at them for longer than a few seconds otherwise you got "arc eye" as in welding.

The result was that you got very clear pictures (black & white in those days).

HD

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According to Wikiwhotsits, digital cameras are inherently sensitive to infra red light and in order not to mess up focus-ing or colour rendering they utilise a IR filter in front of the sensor.

I suppose it might be the presence of the filter that gives the blue/violet effect.

Film cameras also are sensitive to ir but likewise are designed to ignore it as the film emulsions were usually insensitive to it.

You could buy ir sensitive film which you had to store in the fridge to prevent it from fogging and so could not easily use it in hot weather. It was black & white film and you had to use the alternate ir focusing scale or offset infinity point.

I also seem to remember that in the 1970's Kodak had an ir version of Ektacolor or Ektachrome which, like the digital camera with the remote, renderer ir as a range of colours and produced some interesting pop art psychodelic effects when used. I never tried it, it was very expensive, difficult to store and use and practically impossible to get processed when I looked into it.

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