Element: Star Filter

Star Filter is a star shape that has thin rays of light emanating from a central circular area.

What it is based on

Most lenses contain multiple bladed apertures to allow more or less light to pass through the lens. This controls the exposure of the film or video CCD. Wen the aperture is wide open, the opening is perfectly circular. As the lens is “stopped down,” the opening becomes a smaller polygonal shape. For example, a five-bladed aperture will create an opening with five sides as the lens is stopped down. This is why you often see pentagonal or hexagonal shapes on a lens flare.

The aperture also reflects light where the blades intersect, creating a star filter effect. For example, a partially closed five-bladed aperture will reflect five streaks, and result in a ten-point star on the exposed surface. Normally, the rays of light created by this effect are thin and come straight out of the center.

Position

Sets the location of the Star Filter element. The position is always along a line that passes through both the center of the image and the light source. Alternately, you can click inside the Preview Window and reposition the element with the cursor crosshair.

A value of 1 sets the element at a light source. A value of 0 sets the element in the center of the composition frame. A value of -1 sets the element on the opposite side of the frame from the light source.

Brightness

Sets the brightness of the rays and center ball. High values make the rays and their center brighter. Low values make the rays less bright and more transparent.

Scale

Sets the size of the rays. High values make the rays longer.

Thick checkbox

Turned off by default. When this is turned on, the Thickness control is active.

Thickness

If the Thick checkbox is not turned on, this slider does nothing. If Thick is turned on, then Thickness controls how thick the star rays are.

High values make thicker bands, of course. The rays become wide bands of light coming out of center. The thick rays don’t taper off like the normal rays which get wider and more transparent as they extend outward. The thick rays do fade out, but the width doesn’t change.

Thickness works in conjunction with the Width control to set how wide the rays of light are. Depending on how wide you have Width set, the rays can overlap each other and create spikes coming out of the center. This is undesirable for normal lights but for special effects it’s very cool and creates some very interesting patterns.

At left, Thickness set low. At right, Thickness set high.

Width

Sets the starting width of the ray bands as they come out of center. High values make winder bands as with the Thickness parameter.

At standard values, the rays will not overlap. However you can manually set Width to high values by typing a value into the numeric field. This will cause the rays to overlap and create interesting looks.

If the Thick checkbox is selected, then Thickness works in conjunction with the Width parameter to set how wide the rays of light are. You also want to look at how many rays have been set with Count. The Count value will affect how wide a ray has to be to start overlapping.

Angle

Sets the angle of the rays by rotating the star. Essentially, Angle decides where the points of the star sit. High values rotate to the right. Low values rotate to the left.

Count

Sets the number of rays. High values will cause overlap between the rays which can create interesting patterns. Thickness and Width both affect how much overlap there is and what kind of patterns are created. With too many rays, you can introduce moiré artifacts which may be undesirable.

At left, Scale at 1.5, Brightness set medium, Count at 15, Width at 15, Thick turned on, Thickness set medium.
At right, Scale at 2, Brightness set high, Count at 25, Width at 20 (a hand typed value), Thick turned off.

Anamorphic

Use this to create a wide elliptical element or a circular elliptical element. Turned off by default. When the checkbox is checkmarked, the Poly Spread is elliptical. This simulates a common aspect of using anamorphic lenses in cinematography in which light reflections in the lens appear elliptical. When the checkbox is off, the element is round, since light reflections appear round in spherical cinematography.

Color

Sets the color of the Star Filter. Default color is white.