Light Meters - Searching for Middle Gray

Most of us have a light meter built right in to our cameras. Most of those light meters also have several modes, such as matrix metering, center weighted metering, and spot metering (can you tell that I shoot with a Nikon?). But how many of us make full use of our meter? Modern in-camera light meters do a pretty good job of accurately metering the scene, but the information the meter gives us is useless if we do not understand what it is saying.

Light meters attempt to render the scene (or center or spot) middle gray. That is all. The meter sees the light and tells you if you are under or overexposed from rendering that light middle gray. So, if you are shooting a bank of snow, the light meter will cause the scene, if you go directly by the meter reading, gray. It will be two to three stops underexposed, depending on the light. If you are metering black velvet the meter will give you exposure information to far overexpose the image, rendering the black middle gray. You, the photographer, have to understand this and make use of the meter reading, adjusting the exposure to match the scene. Setting your aperture and shutter speed so that the meter reads 0 is usually not the best exposure. In the shot below I metered off of the light higher up in the sky, away from the sun. The sunset is not overexposed and the foreground goes to black, illustrating the encroaching darkness.

North Head Lighthouse, Cape Disappointment State Park, Sunset

Spot metering can be very useful if there exists around you either an object that is middle gray or one for which you know how to expose. A gray card would be a great help. Grass tends to expose correctly at middle gray. In landscape work I can usually find either something close to middle gray to spot meter or I know how to over or underexpose from experience.

Experience is key. Understanding the data the meter gives you gets you started, but there is no substitute for getting out there taking pictures. Later I will discuss the histogram and its use in metering.