The Formatt 4 x 4" 4pt Star Effect Filter is a terrific special effects filter for everything from weddings to night shots. It works best with any point light source such as a match, candle or flashlight. These sources create multiple points of light, or "stars", streaking outward from a central light source. This makes the lighting take on a very effective moody, glittering appearance. This effect is achieved through a series of thin etched lines in the flat optical surface of a clear filter.
Keep in mind that the size and brightness of the star lines are a result of the size, shape, and brightness of the light source.
Note:
Formatt Star Filters are available in 2, 4, 6 and 8pt design
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
Formatt offers 2, 4, 6, and 8 point symmetrical 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