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Infrared Imagery Part 1

27/01/13 - Written by Peter Jenkins

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The majority of cameras (video and stills) are fitted with an infrared filter, which is built into the body of the camera. This is used to filter out any natural infrared light from reaching the film/sensor as it will have an adverse effect on the final image.

Some video cameras have the facility to switch this filter off in order to let IR light through, it is commonly know as ‘Night Shot’. However, with digital SLR cameras it is not possible to do this and so any camera body to be used for IR, has to be specially modified by an engineer who physically removes the IR filter. Once this has been done, the camera will not be ale to be used in its normal mode unless the lens is fitted with a special filter.

Infrared Light

Infrared light cannot be seen by the naked eye. However there are various lamps, flashlights and illuminators that emit IR. They normally emit IR light in one of two frequencies: 850 nanometres or 950 nanometres (nm). An illuminator of 850nm will transmit a feint red glow which is not fully covert but any illuminator transmitting on 950nm will be totally invisible to the naked eye.

IR light also focuses at a different point to natural white light. Be aware that if you are focusing on an object 50cm away, the actual IR point of focus will be approx 5cm behind the object, so this has to be considered when photographing detail.

Video Camcorders

A camcorder with a ‘Nightshot’ facility is very simple to use. Set the camera up, switch on the ‘NightShot’ facility, attach an IR illuminator, set the zoom to your requirements and away you go. You will be able to video in complete darkness. The range of the IR illuminator will have to be tested at various distances and with differing zoom control.

Vehicle registration plates will brightly reflect IR light and therefore can be recorded at further distances when the vehicle itself may not be illuminated.

In Part 2, we look at IR Digital SLR cameras.


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