Basic Metering — Grey card metering
Too many photographers rely solely on their camera’s built in light meter to determine exposure (F-stop, ISO and shutter speed combination). When they look at their digital files, or get their prints back from the photo lab (if they still play with film) they wonder why their prints are not all correctly exposed. To understand why this happens it is important to understand the basics of metering and how the camera sees and processes information.
Camera meters, when used correctly, provide proper exposure readings which yield a full tonal range on the negative or digital file. That said, they cannot think on their own. All reflective light meters, including your camera’s meter are calibrated to give you an average reading of 18% grey (middle grey) on EVERY single shot. They are designed to average out the lightest and darkest tones under normal shooting conditions. Most of the time this exposure method works well since most scenes have a variety of tones from light to dark which average out to 18% grey. The camera meter uses this average to give you a reading which records the full tonal range of the scene if your camera sensor (or type of film you are using) can handle this range.
18% grey (approx.)
But what happens when there isn’t a wide variety of tones for the camera meter to average out? The camera averages them out anyway to achieve 18% grey.
IF YOU FILL YOUR VIEWFINDER WITH A TOTALLY WHITE WALL, YOUR CAMERA METER WILL TRY TO AVERAGE THE ENTIRE SCENE (ALL WHITE) AND GIVE YOU BACK A READING FOR 18% GREY. The print made from that negative will be greyish and might well look like this rectangle.
IF YOU FILL YOUR VIEWFINDER WITH A TOTALLY BLACK WALL, YOUR CAMERA METER WILL TRY TO AVERAGE THE ENTIRE SCENE (ALL BLACK) AND GIVE YOU BACK A READING FOR 18% GREY. The print made from that negative will be greyish and might well look like this rectangle.
Knowing this allows us to compensate as needed for the camera meter’s general readings. The following are good rules of thumb.
If the scene or object to be photographed has primarily dark tones DECREASE the camera meter’s reading by 1–2 stops. (e.g.. brown hair-1 stop, black hair-2 stops) e.g.. from F-5.6 to F-11
If the scene or object to be photographed has primarily light tones INCREASE the camera meter’s reading (open up) by 1–2 stops. (E.g.. blond hair+1 stop, white hair+2 stops) e.g.. from F-8 to F-4
One of the easiest ways to get an accurate reading in ANY situation is to take the meter reading off a grey card. A grey card is a piece of cardboard that is the same tone of grey that your camera meter is calibrated for!!!. It can be purchased in any professional photo store for about 10 dollars or less. By using a proper reading off a grey card, you are assured that the camera meter is giving you the correct average reading.
In the example above using the white wall, by placing the grey card in the scene and taking the reading off that, the camera is basing the exposure on the average it was calibrated to measure!!! The white wall (lighter than mid grey) will reproduce as white. If you throw a sack of coal into the scene, it will reproduce as black since the whole scene is already based on the average which IS the grey card.
In order to take the grey card reading, place the grey card in front of the subject with the grey side facing the camera. Approach the grey card looking through the camera’s viewfinder until only the grey card is visible. This is the reading you will use. Back up, recompose, dial in the grey card reading and shoot. You can also use a reflective light meter on the grey card to obtain the same reading.