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Last updated: Dec, 23. 2008
In our work with motion sensing and on stage camera use we often could take advantage of infrared technology. In short that means that we use light that is invisible to humans. You might already have used it with the night shot feature of some consumer camcorders.
Using infrared light to do the motion sensing has several advantages. It creates some independence of visible light. That means you can use the camera system even in almost total darkness. Some light sources (Video projectors, HMI lamps, moving lights) don't emit any infrared light. Therefor the camera can be made totally blind to those light sources. You can for example point the camera on a performer standing in front of a projection without the projection interfering with the motion tracking. Moving lights also wouldn't interfere with your video interactive system.
Infrared light is the spectral portion of light with longer wavelength then visible red. This ranges between near infrared light (800-1000nm) and thermal radiation (up to 5000nm). In our case we are just using the near infrared range. So don't expect to see humans glowing in the dark due to their body heat (those cameras still cost more than €100.000).
Most CCD chips in the cameras we are using are actually very sensitive to near infrared light. Especially the Black and white cameras, because they usually don't have a built in filter that filters out the infrared light. If you have infrared lighting in your room, you can already use the camera system in darkness.
Standard light bulbs emit quite a lot of infrared light. Fluorescent lamps also, but less. Sunlight also has a lot of infrared. But what do you do to light a dark room and be able to track peoples motion? For surveillance cameras you can get little inexpensive IR-LED modules. They are not really strong enough to light up a bigger room or a stage. Especially as we are often using wide-angle lenses. The emission of those modules is most often pretty narrow focused.
There are professional IR LED lamps as described in the table below with high light output and also high price .
But there's a simple trick that often helps: Use a standard tungsten theater light (3000K) and add color gels til the visible light is cut out. Usually a dark blue and a dark red on top do the job. Surprisingly there's still a lot of infrared light coming out. Get high temperature gels and if you have a dimmer reduce the power for the infrared light, otherwise your color gels won't life very long ;-(
Using a IR sensitive camera and appropriate infraed lighting isn't really enough to become independent of visible light. For many applications (i.e pointing the camera towards a projection) you have to make sure that your camera becomes blind to visible light. Different companys sell lens filters with IR pass characteristic. They are made for IR-photography and don't have a mounting that directly fits onto CCTV camera lenses. You have to improvise a bit. Or get an adapter from us
Infrared accessories, all equipment available from us, write to firstname.lastname@example.org, online shop to come soon.
|Analog Video camera||Black and white surveillance camera; Sony XC-EI50 with Tamron Vario lens 4.2-10mm, wide angle, great resolution and light sensitivity.||high sensitivity to infrared, automatic aperture can be switched off.||requires you to buy a video board (i.e. FALCON PCI Bus Framegrabber below), expensive||very good!||500€|
|Analog Video camera||Black and white surveillance camera; Santec VTC1320, good quality,||cheaper alternative compared to Sony camera||bit bulky||160€|
|Infrared filter||Tamron wide-angle lens 1/2" 4-12mm, infrared compensated focus||good quality, good price||no direct filter attachment||100||Tamron lens|
|Infrared filter||Heliopan Infrared pass filter, 830nm||cut's out all visible light||50€||Heliopan 830|
|Filter adapter||Kaiser 96656, Filter adapter, which allows you to attach infrared or other filters (49mm) to any camera which has a diameter between 25 and 62mm||looks a bit bulky||very useful!||20€||Kaiser filter adapter|
up to 80° angle,
|high power||price, limited emission angle||