Star filter / Cross filter
Sterfilter / Cross-filter · Lens & optics
A filter with finely engraved lines that turn point lights into stars with 4, 6 or 8 rays.
Common at Christmas markets, evening city lights and events where bright sources should pop. The number of points depends on the line pattern. A small aperture (f/16 or narrower) gives a similar effect without a filter, but less pronounced. Cheap star filters can reduce sharpness; serious users go for Cokin or Hoya.
Tools that help with this: