Special-Effects Filters: Star Filters

Filters discussed on this page may have a thread size (i.e., diameter) larger than 28mm. In fact, they are either of 37mm, 39mm, 43mm, 46mm or even 49mm. Hence, appropriate step-up rings are required, and, as a result, effects created with these larger filters may not fit completely on the image. Moreover, since step-up rings may block the flash sensor, using these filters may prevent you from using internal/external flashes. Proper exposure compensation applied to the camera and/or flash may be required.

Star filters turn point light sources and specular highlights into stars. Commonly seen star filters can generate four to sixteen points stars. A star filter consists of two glasses. The top one is rotatable and has a grid etched into the glass surface. The following image is a four-point star filter. The etched grid is easily seen. The distance between two parallel etched lines is an important factor. More precisely, the wider the distance, the fewer number of stars. This distance can be 1mm to 4mm. The 2mm version is the most common one. Some star filters can even create variable star shapes. That is, in the case of 4-point star, the two etched lines do not have to be perpendicular to each other, and can be rotated to form any desired angle.

A four-point star filter

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Using a star filter is simple. Just mount it on the lens and rotate the front ring like using a Circular Polarizer. The orientation of the stars will change as the front ring is being rotated. In practice, only stronger point light source can create star shapes. Moreover, stars may disappear completely when the aperture being used is too small. Therefore, adjust the aperture, or check your LCD monitor for the best result.

The following are examples of using a 4-point star filter. The first image was taken without a star filter; the second and the third were taken by rotating the front ring so that the orientation of the stars are different. It is clear that the stronger the light source, the larger and brighter the star. Note that the orientation of stars do affect the composition of your image. You can always rotate the front ring to select the best orientation.


Without filter	With 4-point star filter
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Because the star filter being used is of 37mm that is larger than the size of the on-camera lens, one of the four spokes appears in the left side of the third image above, even though the light source is not in the scene. (But, the light source is in the larger scene covered by the 37mm filter.) A similar effect appears in the second image below.


Without filter	With 4-point star filter
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As long as there are point light sources or highlights in your scene, you can use star filters. The following are more examples.



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The following image is taken with a 8-point star filter.

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