Tiffen 4 x 5.65" 4 Point/3mm Grid Star Effect Glass Filter create multiple points of light, or "stars," streaking outward from a central light source. This can make lighting within the scene take on a more glittering, glamorous appearance. This effect is produced by a series of thin lines etched into the flat optical surface of a clear filter.
The size and brightness of the star lines produced are first a function of the size, shape, and brightness of the light source.
You have additional control through the choice of a particular spacing between the lines on the filter; These spacings are measured in millimeters and range from 1mm to 4mm
A 1mm spacing has twice as many lines as a 2mm spacing; It will produce a brighter star for any given source
Lines in one direction produce a two-pointed star, just a streak through the center of the light
Tiffen offers 4, 6, and 8 point symmetrical star effects as well as additional asymmetrical star patterns through their exclusive Hollywood FX Series (North, Hyper, Vector and Hollywood star effects)
With an 8 point filter, the many star lines may tend to overpower the rest of the image, so use it carefully
Generally, mid-range apertures or larger are sufficient to achieve a good star effect; Always test before critical situations