The technique required when using an incident meter to read flash or hot (quartz) lights is tricky and can benefit from consistency in your technique. Part of this has to do with both where we place the dome and where we point it. Let’s say, for example, we have a subject lit by two broad light sources (the main and the fill), with the main light 45° – 60° away from the lens axis. The fill light is on the opposite side of the lens axis from the main light, closer to the lens axis than the main light, and farther away from the subject than the main light. If we place the dome on the fill light side of the face, we will get a different reading than if we place the dome on the main light side of the face, even though the difference between the two positions is only about six to eight inches. We will also get a different reading if we have the axis of the dome pointed directly at the camera lens or angled towards the main light instead. If you were to ask me which position is best, I would answer that it doesn’t matter as long as you do it the same way every time. If you do this, you will have eliminated another variable in your technique. As long as your technique is consistent, you can figure out the correction required by looking at the histogram from a single photograph.
Let’s continue along this path of eliminating variables. Not only do you have to consider where you place the dome, but you also have to be sure that your position, when you take the reading, doesn’t affect the amount of light hitting the dome. Many inexperienced photographers will walk up to the subject and, as they stand directly on the axis between the lens and the subject, place the dome in front of the subject’s nose and take a light reading. This might be okay except for the fact that your standing along the lens/subject axis means that your body might be blocking some of the light from hitting the dome.
Let’s look at another example. Say you are working in a flash-lit scenario and you were using a grid spot that acts as a hair light. Once again, if you were to stand on the axis between the camera’s lens and the subject, placing yourself directly in front of your subject, the exposure setting your meter suggests would be affected by whether you were wearing a black or white shirt. When wearing the black shirt, you would be acting as a negative fill reflector; when wearing the white shirt, you would be acting as a positive fill reflector. I can promise you that each exposure reading would give you an exposure suggestion that would be wildly different!
To eliminate both of the variables mentioned in the last two paragraphs, I always stand to the side of my subjects and never in front of them. If I’m working with electrically powered lights (flash or quartz hot lights), I always stand on the fill light side of my subject. I choose to stand on this side of my subject because, by definition, the fill light is always less powerful than the main light, so it is a smaller component of the total light hitting the subject. This means that if I block it slightly with my body as I take a meter reading, the reading will be less affected because the fill light is less powerful. Likewise, I always extend the meter into the scene and place the dome at my subject’s chest height or under their chin. This meter position doesn’t offer as accurate a reading as when the dome is placed in the middle of the subject’s face at their nose tip, but I prefer not placing it right in their face because I think it is a big intrusion on my subject’s space and hurts our rapport. Because of this I have to remember to adjust my reading accordingly because the subject’s chest height is usually farther away from the light source than their eyes.
This overhead view of a photographer using an incident meter reveals a few important details about consistent metering technique. Note the photographer holding the meter has positioned himself on the fill light side of the scene so if, by chance, his body obstructs some of the light hitting the meter’s dome it is blocking the less intense fill light instead of the more powerful main light. Even so, he has carefully positioned his body so that there is little chance of blocking any of the light hitting the dome. Although the meter’s dome was intentionally drawn oversized for clarity, note that it is “feathered” so as to point along an imaginary line between the lens axis and the center of the main light.
Some photographers like the look of a strong hair light, while others prefer one that provides just a hint of light on the back of the subject’s head (as seen here). Regardless of your preference, if you are wearing a white shirt while standing directly in front of your subject while using an incident meter, the reading will be affected by the hair light’s spill bouncing off your white shirt and hitting the meter’s dome. Photo © Jan Press Photomedia, Livingston NJ.