**Near-Infrared Photography with an inexpensive webcam**

	Silicon image sensors and photodetectors are most sensitive in the
near-infrared part of the electromagnetic spectrum, roughly at 800 nm.
These types of image sensors are found in all digital still cameras, all
webcams, and all video cameras manufactured today.  As a result, these cameras
have at least some level of sensitivity to infrared.  Most such cameras, with
the exception of monochrome security cameras intended for day/night operation,
incorporate infrared-blocking filters to keep most of the infrared from
reaching the image sensor.
 
	The photos on this page were taken with a Philips/Gemini J44414 webcam
that was modified to turn it into a near-infrared camera.  The modifications
consisted of removing the camera's infrared filter, which in this camera
was glued to the back of the lens assembly.  The infrared filter was replaced
with a visible-blocking filter made from a piece of exposed and developed color
negative film.  Color film works well for this purpose because it has three
types of pigments with narrowband absorption characteristics at the red, green,
and blue parts of the visible spectrum.  The film is transparent to infrared.

	The infrared webcam has a visible "twin" (that is an unmodified
J44414) that was used to take comparison photos in the visible spectrum.  An
easy way to distinguish between the visible and infrared photos is that the
visible photos are all in color, whereas the infrared are monochrome.  The
black and white look of the infrared photos is due to the CMOS image sensor's
color filters being ineffective at infrared, rather than due to any re-touching
of the photos.  Some near-visible infrared sources, such as CD player lasers
(780 nm wavelength) look pink to this camera.

	There are two sets of photos:  One is of some common objects and scenes
shot in infrared as well as visible.  The other are infrared shots taken during
the construction and test of a intensity LED infrared illuminator consisting
of 100 LEDs.  The LEDs are rated for a peak emission wavelength of 880 nm.