Under the umbrella term masks you will find three different groups of products which are important aids for astrophotography:
- Focus masks help with focusing. Depending on the design, the terms Bahtinov mask or Scheiner mask are also used.
- Flatfield masks deliver a uniformly illuminated bright surface that allows the camera sensor to be correctly calibrated in order to compensate for vignetting. Without this correction, astrophotos appear darker in the corners.
- Spike masks produce stars with bright spikes. Some astrophotographers consider this to be particularly aesthetically pleasing. Newtonian telescopes produce these spikes due to the secondary mirror mounting. For refractors, these masks are required to produce this effect.