What Is Infrared Photography?

An infrared photograph is a revelation of an astonishing world that would remain unknown to us without special equipment. In black-and-white infrared landscape images we see deep black skies and brilliant white leaves and grasses; in portraits we see an inner glow that comes from just below a person’s skin.

The images on this site are not thermal imaging or false color. Nor are they film-based; they all had their source in digital camera sensors. The infrared information that is received by the camera sensor is translated by computer software into black and white tones that look like normal black-and-white photographs – with a remarkable difference and often with great drama.

Normal color Normal b&w Infrared b&w

Human Vision and Infrared

Human vision is sensitive to electromagnetic radiation from approximately 400 to 750 nanometers - without instruments we cannot see into the shorter ultraviolet (UV) or into the infrared (IR). That narrow range encompasses all the colors that make the world appear so wonderful to us, from the darkest reds through yellows and greens and blues to the farthest reaches of violet. Some insects can see into the ultraviolet; and some snakes can see infrared at night.

Digital Sensors and Infrared

The sensors of many digital cameras can "see" into the UV and near-IR ranges, which is a problem because those different wavelengths focus at different distances from the lens, making for blurry images. Therefore the sensors are outfitted with filters to block UV and IR so that only visible light is recorded.

Those filters are not 100% effective, though, so UV and IR images can be recorded by many digital cameras by using special filters in front of the lens. Such filters block the visible radiation and allow only the desired wavelengths to reach the sensor. These filters appear black, so the photographer cannot see through the lens to frame and focus the shot. The density of the filter also means that little light reaches the sensor, so exposure times are long. The images here from the Mojave Desert in 2004 were made with a standard Fuji S2 digital camera with an 89B filter.

The infrared images here, with the exception of those from the Mojave Desert in 2004, were made with a customized Canon 400D (aka "Digital Rebel XTi"). The manufacturer's UV-IR filter was removed and replaced with a filter that blocks all electromagnetic radiation below 715 nanometers and above 1200 nanometers. Also, because IR does not focus at the same distance from the lens as visible light, the auto-focus sensor was recalibrated. So the camera records images in the near-IR without any special filters. It's like working with a standard digital SLR camera - the scene is viewed through the viewfinder, the auto-focus works correctly, and shutter speeds are just as fast.

Links

Infrared explained (Wikipedia)
Infrared filters, cameras, and information (maxmax.com)

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