South Haven after Sunset

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South Haven Lighthouse

This shot had been on my wish-list for some time and I finally made it happen last fall on a quick trip I made to southwest Michigan. A number of Lake Michigan lighthouses have retained their catwalks, but few are lit as nicely as South Haven’s. The catwalks were originally designed to give the keepers access to the lighthouse during stormy weather when it wasn’t safe to walk on the pier. But on a calm night they have a peaceful beauty.

It’s a bit hard to see on this small image, but each of the lamps in this photo is surrounded by a starburst of light. This is another dependable phenomenon caused by specular highlights in a photograph (see the previous post on circles of confusion). In this case the starbursts are caused by the tendency of light to bend (diffract) around edge of the aperture in a lens. Since apertures are made of overlapping blades, the diffraction is uneven and causes the starburst pattern.

The diffraction effect is most pronounced at small apertures (because the ratio of the circumference to the area of the circle is larger). The number of blades in the aperture of your lens will determine how many rays are in the starbursts, so there is lots of room to explore this effect with different lenses and different apertures. You’ll also find the effect is more pronounced at longer shutter speeds. I took a series of photos of this scene as dusk faded into night, and the starbursts became more pronounced as the light in the sky diminished. For this shot my exposure was 25 seconds at f/11.

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