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Glossary | Telescope accessories | General | Type of build | Pass filters

Filters with a pre-determined bandpass range

Pass filters allow only light of a certain wavelength range to pass through. This bandpass range for astrometric filters is very precisely defined. Unlike line filters, the bandpass range is much wider and not matched to a specific spectral line. The aim of an astrometric pass filter is not to suppress light pollution, such filters can be found under the CLS or UHC categories.

The term pass filter is also used to mean filters that allow long-wave infrared (IR) or short-wave UV light to pass through, but not the light visible to the eye. IR pass filters are popular in planetary photography because the disturbance caused by the terrestrial atmosphere’s seeing is not so noticeable in the long-wave range. If the camera sensor is sensitive to this long-wave range, a sharper image is possible than in the visible wavelength range.