Filter that blocks infrared light, passing only the visible spectrum. Prevents color shifts in digital camera sensors.
Technical Details
Standard IR filters exhibit a transmission of >95% for visible light and <1% for infrared light above 750 nm. The blocking effect is achieved through interferometric cancellation using 20-50 alternating layers of materials with different refractive indices, such as titanium oxide (n=2.4) and silicon oxide (n=1.46). Hot mirror variants reflect IR radiation back, while absorbing filters convert the energy into heat. Motorized IR filters in professional cameras can switch between day and night modes, with the mechanical movement taking 0.2-0.8 seconds.
History & Development
The first IR filters appeared in 1975 with the advent of the first CCD cameras, as these sensors were significantly more sensitive to infrared than film emulsions. Sony introduced the first integrated IR cut filter in the Betacam series in 1981. Red Digital Cinema revolutionized the system in 2007 with the Red One by offering interchangeable OLPF/IR filter combinations (Optical Low Pass Filter). Arri implemented permanently installed IR/UV cut filters in the Alexa series in 2010, with 99.9% blocking above 750 nm.
Practical Use in Film
Without IR filters, characteristic color shifts occur: black textiles appear reddish, skin tones become unnaturally rosy, and vegetation takes on a magenta cast. "Mad Max: Fury Road" (2015) temporarily removed IR filters for its desert sequences to enhance the surreal color grading. Daylight shots with removed IR filters require additional ND filters (Neutral Density), as 30-40% more light reaches the sensor. With LED lighting, the IR filter is essential, as many LEDs exhibit strong IR emissions above 800 nm.
Comparison & Alternatives
UV filters exclusively block ultraviolet radiation below 400 nm, while IR filters limit the upper spectrum. Combined UV/IR filters integrate both functions into a single element. OLPF systems (Optical Low Pass Filter) additionally reduce moiré effects through controlled image blurring. For night vision shots, IR filters are mechanically or electronically deactivated to utilize IR illumination. Software-based IR correction in post-production cannot fully replace physical filters, as already oversaturated color channels are not reconstructible.