Optical filters are extremely useful devices that are used in all kinds of industries for all kinds of applications. They are generally made of glass or plastic, and are either dyed or covered in interference coatings. They are used to selectively transmit light by reflecting certain wavelengths and allowing others to pass through them.
The Three Types of Optical Filters
Most optical filters fall under one of these three main categories: optical longpass filters (LP filters), optical shortpass filters (SP filters) and optical bandpass filters. LP filters, SP filters, and optical bandpass filters each carry out their own specific function, and can be used for a vast array of specific applications.
Optical LP Filters
LP filters are used to block shorter wavelengths and transmit longer wavelengths. They are often used in fluorescence microscopy in barrier filters and dichroic mirrors.
Optical SP Filters
SP filters are essentially the inverse of LP filters. While LP filters attenuate shorter wavelengths and pass longer wavelengths, SP filters attenuate longer wavelengths.
Optical Bandpass Filters
What do you get when you combine an LP filter with an SP filter? You get an optical bandpass filter. Optical bandpass filters only transmit wavelengths that fall within a certain range, while blocking wavelengths that fall outside of said range on either side (both longer and shorter wavelengths).
Because optical bandpass filters only pass specific wavelength bands, they are great for applications that require observation of really specific wavelengths. Optical bandpass filters play an important role in astronomy, as they are often used in telescopes.
Though you may not realize it, you probably interact with optical filters in one way or another all the time, as they are used for everything from factory automation to motion analysis to aerial imaging to agricultural inspection. Now, you know at least a little bit about how they work.
