How do umbrellas help control reflection in photography?

Umbrellas, usually white, are used in Photography to modify light by making the light source larger. The effect is to spread the reflection and soften the shadow. Many great shots can be made with a single light "bounced" or shot through a white umbrella, and a piece of white foam board used on the opposite side of your subject as a reflector for a shadow "fill."

One way to understand what photographic umbrellas do is to go outside on a sunny day and look at the shadows cast by objects. Try something relatively small, such as a fire plug. Its shadow is dark and sharp edged because the sun is a "point source" of light. The sun is relatively small in the sky, which is why it casts a dark sharp shadow and makes specular reflections. Inside the photo studio, a spotlight or a clear bare bulb has the same effect. Study any reflections on the object. They are what we call "specular." They are very bright and small and sharp. They may even hurt to look at.

If you happen to have a white umbrella (not a classic black one), take it with you outside and, after you've studied the effect of direct sun, open your white umbrella and interpose it between the sun and the object. What happens? Yes, the light level drops because you're shading the object, but look what else has happened: the shadow gets soft edged and opens up - looks more gray than black. The reflections are now soft and fuzzy, not specular any longer. What you've done is the same as when a cloud covers the sun. Some of the light comes right through the "cloud" (your white umbrella), but the original point source has now been spread out, softening both the shadow and the reflections.

In the photo studio, "bouncing" the lights from the insides of white umbrellas, or shooting the lights through white umbrellas, spreads the light over the whole width of the umbrella. The effect is similar to a cloudy day. The reflections from a shiny object are spread over a wider area, and the shadows are softer and more "open." If the object is small and the umbrellas are large the effect is enhanced.

But umbrellas and their close relatives, light boxes, are still directional (that is, the light can be seen to be coming from a specific angle). They're wonderful for portraiture and many other subjects. If you're photographing small shiny objects and want a nearly shadowless look, try directing your lights at the ceiling and walls (the camera room must be small and painted white). The light will be now coming from everywhere, like an overcast day, and the reflections will be very spread out and the shadows very soft.