Jay Holben explains the concept of Infrared (IR) contamination in cameras and tests out several IR filters on the RED Epic and Alexa.
Let’s take a brief trip back to high school science class and revisit the electromagnetic spectrum. Sound waves, radio waves and gamma waves represent specific frequencies in the electromagnetic spectrum, the range of all frequencies of electromagnetic radiation. The spectrum includes wavelengths from 1 angstrom (one ten-billionth of a meter, or one-tenth of a nanometer) all the way up to AM radio at 100 meters in length and beyond.
A tiny portion of this spectrum—from about 380 nanometers to 700 nanometers—corresponds to light visible by the human eye. It’s via this small area of the spectrum that we see the world. This segment of the spectrum is sometimes referred to as “visible light,” but that’s a redundant term. All light is visible. If it’s not visible, then it’s not light; it’s radiation.
Just before the range of light visible to human eyes is ultraviolet radiation (UV), which we know as the harmful rays from the sun that fry our skin. Ultraviolet wavelengths range from 10 nm to 380 nm.
Just before the range of light visible to human eyes is ultraviolet radiation (UV), which we know as the harmful rays from the sun that fry our skin. Ultraviolet wavelengths range from 10 nm to 380 nm.
Beyond light is infrared radiation, which takes up a large portion of the scale, with wavelengths from 700 nanometers to 1 millimeter. The infrared part of the spectrum is also called “radiant heat.”
Our eyes are not sensitive to radiation, at least not in ways we can visually interpret, but digital sensors are, which causes some problems. Remember that both light and radiation are forms of heat, and it can be very difficult for an electronic circuit to differentiate between the various forms of heat as to what is good (light) and what is bad (radiation). All digital cameras (except those specially designed for “night vision”) feature infrared cut filters to limit the amount of infrared radiation that strikes the sensor and can be misinterpreted as light.
Good article, although I thought it was worth pointing out that contrary to what it says in the first paragraph, sound waves are not part of the electromagnetic spectrum.
Good catch