What is an Infrared Filter and How Does It Work?

An infrared filter is a device that is specifically designed to block visible light and only allow infrared light to pass through the lens. The reflection-type infrared filter, also known as a cold optical mirror, is manufactured on optical white glass by vacuum coating. It reflects visible light and lets infrared light through, and the outside of this filter looks similar to that of a mirror. In astrophotography, many photogenic lenses (such as emission nebulae) glow in the far red and near infrared. The full spectrum filter, or transparent filter, doesn't have many uses on its own, but it offers the flexibility to switch between different external infrared filters and capture images without a tripod.

This is why the term IR filters is often used to refer to filters that let infrared light through and block other wavelengths. It's important to note that the IR sensitivity of the absorption-type infrared filter is greater than that of the reflection type. Umicore has extensive experience designing a wide range of complex, high-performance infrared filters for many different wavelengths. This allows you to switch from infrared to normal recording with a single camera; however, opaque infrared filters block the composition in DSLR cameras without a live viewing function. Since the dyes in processed film block several parts of the visible light, but they are all quite transparent to the infrared, the dark black sections of any processed film (where all visible colors are blocked) only allow infrared light to pass through and are commonly used (superimposed on top of each other if necessary to better filter visual light) as an economical alternative to expensive glass-backed filters. Infrared cutoff filters, sometimes called IR filters or heat-absorbing filters, are designed to reflect or block near-infrared wavelengths as visible light passes through. The camera's white balance was not designed to work in infrared, and the camera may not be able to measure white balance correctly, resulting in unexpected results.

There are also filters used in solid-state video cameras (CCD or CMOS) to block infrared because of the high sensitivity of many camera sensors to near-infrared light.

Clément Vermeulen
Clément Vermeulen

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