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Studio Photography
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● Creative Lighting Techniques for Studio Photographers
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Credits
I'm grateful to John Tice (jontic@vt.edu) for educating me about specular/diffuse light.
Text and pictures copyright 1982-1995 Philip Greenspun
philg@mit.edu
Reader's Comments
Putting a honeycomb grid over a softbox does not necessarily turn that diffuse light into a specular light,
but it does head it in that direction. It all depends on the size of the holes in the honeycomb and the
thickness of the honeycomb material. I've used largish diameter honeycomb hole material that
maintained a pretty diffuse lighting pattern in terms of the subject, but still gave me a fairly quick cutoff
outside the lit area. The Degree of Specularity depends solely on the angle subtended by the light in
relation to the subject. In other words, if you're standing in the middle of the desert and being lit by the
entire sky (and no sun), your light subtends an angle of almost 180 degrees relative to you, the subject.
That's seriously diffuse light. On the other hand, if you're being lit ONLY by the sun, which is, relative
to you, a very tiny one or two degrees of angle, the sun is rapidly approaching being a point source, and
the shadows are very hard-edged indeed, and that's seriously specular light. The sun could actually be a
very diffuse source if you were only a few miles from its surface. At that point, the sun, which is HUGE
relative to you, would be taking up nearly half of your available vision, as does the sky in the desert, and
it would be diffuse. And, of course, you'd be fried. The interesting point, here, is that for any given size
of light source and any given size of subject smaller than the source, the closer you move the light, the
more diffuse it will be. Most light sources are actually combinations of specular and diffuse light. If you
take a piece of translucent fabric and put it between the light and the subject, you usually get that
combination. The closer you bring the fabric to the light, the less fabric area you're lighting, the
http://www.photo.net/studio/primer (10 of 17)7/3/2005 2:18:01 AM