Filmmaking > Camera & Lighting
Light Meters
There are two methods of measuring exposure: incident light reading and reflected light reading. The person who taught me about exposure was a Dutch lighting director named Alex von Saher. He could talk for days about how to take a reading.
Incident light readings are taken from the point of view of the talent where the meter faces the camera. This is used for scenes that feature people on camera with an area being lit of average brightness. The cameraperson stands where the talent will stand and aims the light meter at the camera. To meter a specific light, use a flat disk in place of the dome on the meter. It is wise to use two light meters as a habit to double check readings. I use a Spectra Light meter and a Minolta Digital meter. The Spectra requires that I insert a slide into it for the ASA of the film. The reason for the dome on the meter is that it picks up all the light hitting the meter. It is best described as a hemispherical plastic collector of all the light hitting it. In effect, it’s three-dimensional and resembles the shape of a human face. By adding a flat disk to the meter, you then get a directional reading. This allows you to specifically point it at a key light for instance and get a measurement for just the key. You can then point it toward your fill light and get it’s reading. This allows you to determine if you want to reduce the foot-candles on your key or fill lights by changing the light, its position, or the need for a scrim. Once you’ve determined the intensity (foot candle level of a scene) you can then determine the continuity of your key light levels. This allows you to work at the same aperture setting for the entire scene and maintain the same depth of field. When measuring for the key light, many cinematographers prefer to shoot scenes at a particular f-stop, for instance, f/4. Depending on the particular lens being used, f/4 will give a certain desired “look” that the cinematographer is striving to achieve.
A reflected light reading is taken from the camera’s point of view. Cameras with auto iris, such as most video and still cameras, have built-in reflected light meters. With built-in reflected light meter, when you shoot a subject against a sunset, the meter will give you an average reading making the subject appear dark.. Tilt the meter downwards when taking an exterior reflected meter reading to avoid including too much bright sky. This also applies when taking a reflected reading with a built-in, through-the-lens light meter. Optimally, the reflected reading should be taken off a gray card which has a reflectance of eighteen percent.
When would you prefer to use a reflected reading instead of an incident reading? It is mainly used on exteriors and large outdoor panoramas. This involves color and contrast variations that are beyond your control. If you are shooting an actor in such a situation, an incident reading won’t take into consideration the brightness of the background exterior. A reflected reading is more suitable in this example. If the actor is also being illuminated by lighting instruments, you may want to do both type of readings and then interpret what the aperture should be set. Another factor is what immediate background the actor is against. If it is a white truck or sign, for instance, the reflected reading will cause the actor to be overexposed. One method used by many cinematographers is to take a reflected light reading of their hand (if the light is about the same and flesh tones are similar) and then interpret the wide shot reflected reading and adjusting it accordingly. The other choice is to use a spot meter and measure the actual actors face and then interpret the balance between the wide reflected reading and the actors face.