Lighting solutions are often offered in the form of an established photographic principle; for example, “The angle of incidence equals the angle of reflectance.” That’s photospeak to explain how to photograph a mirror or reflective surface, or evenly light a copy stand or background; however, it doesn’t explain anything unless you first understand the two types of light meters: incident and reflected. More on that later. First, a how-to light it.
No Glare Technique
One of my clients is a Vietnam vet with an avid interest in military history, particularly the Civil War, which makes sense because he (and I) live in Atlanta, the only American city ever destroyed by war. He bought a full-size, Bowie-style, presentation knife made in 1861 by ironworks owner Mark Anthony Cooper for the then Fire Chief of Atlanta, Charles Beerman. The extraordinary detail of presentation knives is acid-etched into the steel using beeswax to form the pattern, and then tiny embellishments are added afterwards with steel scribes (similar to scrimshaw in ivory).
Our challenge is to photograph the entire knife and its wooden and brass hilt so that the detailed finishing work can be seen easily. Here’s an unretouched view of the knife with a ColorChecker.
Notice the nut holding the knife level under the blade just before it starts to curve toward the tip. There’s no glare on the brass finishings on the hilt, nor any on the blade, even at the upper left where it curves inward. Glare is a reflection from the light, causing a blown-out specular highlight. A specular highlight is a mirror image of the source of light shown in a reflective surface of the subject. In this case, the specular highlights are absent on purpose.
The technique is to create a source of light large enough to cover the entire knife, and then angle it so its surface won’t show in the bright metal on its blade or hilt. The setup is simple, too. First, I put down a 53″-wide roll of Savage Super White Paper over a table to serve as a background. Next, I placed a Chimera 82×42″ panel frame covered with diffusion fabric between two stands. Two Dynalite location electronic flash heads illuminate the diffusion. The panel is placed so that its light wraps indirectly around the knife. Fill light is bounced back into the scene with a 48×48″ piece of white foam core.
I made the shot tethered to a Mac Pro, so I was able to view the results at 100% right away. The detail that this light reveals is better than any magnifying glass. Look at this close-up view of the presentation mark made with a Sigma 150mm f/2.8 macro lens.
Back to the Rule
Here’s how the angle-of-incidence-equals-the-angle-of-reflectance principle plays in the setup for the knife. The camera doesn’t see the light from the diffusion panel because the light’s angle is illuminating the background and then bouncing into the foam core reflector. The camera isn’t in the path of the light’s reflected angle.
So, what does that have to do with the types of light meters? Incidence is the light falling on a subject, and incident meters measure that light. From the subject’s position, point the dome at the source of light. Use the reading as the exposure on the camera. Knowing how much light the subject receives is really important, as it’s the only way to set a truly accurate exposure on the camera. The reflective meter measures light that has already illuminated the subject. As its name implies, this meter takes into account the amount of light a subjects sends to the camera.
So There You Have It
Demystified, the angle of incidence equals the angle of reflectance means that the angle of the light falling on the subject is equal to the light bouncing off it. This principle is useful in all kinds of lighting situations, for example:
• Do you want to know if a reflector is really catching the light? Go to the subject position. Look at the reflector. Do you see the light source in the reflector? Great! The angle of incidence (light falling on the reflector) equals the angle of reflectance (light you’re seeing reflected onto the subject once you step out of the way.)
• Are you using flash and see a glare from it in the photo? Stand in front of the light, looking at the glass. You’ll see the camera (reflectance.) Move to one side or the other until you no longer see the camera. Put the light there, and you’ll have no more glare.
• Do you want catch lights in a subject’s eyes? Ask the model if she can see the light. If the answer is “yes” (incidence), it means there will be a catch light (reflectance.) “No” means there won’t be any at all.
• Do you have a setup with a mirror in it? Show the mirror (incidence) what you want it to show the camera (reflectance.)
Cheers! Until next time, light well and prosper.