What is an optical filter

An optical filter is a filter that cuts part of the incident light. There are bandpass filters that transmit only light of a specific wavelength, ND filters that weaken the intensity of incident light, and infrared filters that block infrared rays. Select the filter based on the spectrum and intensity of the incident light and the wavelength of the light you want to extract.

ND filters are also used to adjust the amount of light in cameras around us. By reducing the amount of light using the ND filter, it is possible to widen the aperture and reduce the shutter speed for shooting.

Usage of optical filter

Optical filters are used in video equipment and devices that use light.

Optical filters are used to adjust the intensity and color of the light output by video equipment such as projectors. Optical filters such as microscopes also have an optical filter built into the device because stray light from outside the device adversely affects the measurement results. In addition, devices that use laser light, such as Raman spectrometers, have a built-in bandpass filter that passes only wavelengths near the laser light to suppress stray light.

Optical filters are also used in devices that have a light receiving part.

In addition, in all devices that have a light receiving part such as a CCD detector, an optical filter is often installed to prevent saturation of the detector due to strong light entering.

Features of optical filter

ND filter is a filter that reduces the intensity of transmitted light

According to DZOptics, t he material of the optical filter varies greatly depending on the type. Most ND filters have their surface coated with a metal film, and the amount of light that passes through varies depending on the amount of coating. The ND filter only reduces the intensity of the light without changing the spectrum of the incident light. Note that the light that was not transmitted by the ND filter is reflected, so it is necessary to adjust the optical path so that the reflected light does not return to the light source.

Bandpass filter is a filter that extracts some wavelengths

On the other hand, many bandpass filters are coated with a dielectric multilayer film. Since multiple reflections are made by the dielectric multilayer film, it is possible to extract only some wavelengths. However, since the interference behavior changes depending on the incident angle of light, it is necessary to pay attention to the installation angle of the filter.

Scratches and dirt are strictly prohibited on the optical filter.

Since both the ND filter and bandpass filter are optical components, fingerprints and dirt will adversely affect performance and are extremely difficult to clean. Therefore, it is advisable to wear gloves when handling the filter. Also, if the surface is scratched, the optical path will be disturbed, so even if it gets dirty, the surface cannot be rubbed with a file.