Sources
There are many sources of stray light. For example:
- Ghost orders in diffraction gratings. These can be caused by periodic variations in the spacing of grooves in ruled gratings, for instance.
- Light scattered towards a telescope from particles along the optical path to a star.
- Light emitted by components of the optical system.
- Infrared optical systems are, obviously, especially susceptible due to thermal radiation.
- Reflections from lens surfaces.
- Anti-reflective coatings are used to reduce stray light.
- Narcissus - Specifically, thermal radiation from the infrared detector reflected back to itself from lens surfaces.
- Light scattered from the surfaces of supporting structures within the optical system.
- Diffuse reflection from imperfect mirror surfaces.
- Light leaks in the enclosure of the system.
- This might be the first cause to come to mind, but as this list shows, it is hardly the only source of stray light.
Read more about this topic: Stray Light
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