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How can you control the size of "starbursts" from light sources in photographs? For example, the lights on the shore in this photo have very sharp and long starbusts:


Is it possible to control this through a combination of aperture and shutter speed? Or, is this more determined by the camera lens?

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@Matt Grum gives some good advice in a closely related discussion. –  whuber Apr 7 '11 at 6:12

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up vote 11 down vote accepted

The effect is caused by diffraction. Typically this occurs stronger at smaller apertures - open your aperture (use a smaller f/number) to reduce the effect.

The shape of the star is caused by how many blades your aperture has. A lens with a rounded blade aperture should also reduce the effect.

You can read some basic, non-super-technical information about it here:

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+1 - At first I was thinking a star filter, but I think you have it. The points on the star line up with the number of aperture blades in the lens used for the shot. –  John Cavan Apr 7 '11 at 3:21
The number of star points is determined by the number of blades the lens has. I will experiment with opening up and closing down the aperture to see its effects on the starbursts. Thanks. –  bperdue Apr 7 '11 at 4:03
The number of blades in the aperture mechanism is important for the look of the "star". An even number gives the same number of light-rays as blades; an odd number gives twice as many. –  Staale S Apr 7 '11 at 6:53
+1 for the reference –  labnut Apr 7 '11 at 7:06

I think rfusca is correct as to the reason for it in your linked image, but it's also possible to get the effect using a star filter and then the size of burst is dependent on the light source that triggers it.

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It's probably not best to use star filters in a landscape/cityscape scenario like linked though, right? Typically you use smaller apertures for increased DOF in these cases, but filters that cause different bokeh shapes (which is what this is really, right?) require fairly large apertures. –  rfusca Apr 7 '11 at 3:33
@rfusca - No, this isn't a false aperture over the front of the lens, so it's not quite the same as shaped bokeh. In this case, it's either a grating in the filter or prisms that cause the effect, not the aperture shape. –  John Cavan Apr 7 '11 at 3:47
Ah, gotcha. - +1 –  rfusca Apr 7 '11 at 3:54

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