Saturday, November 14, 2015
Understanding Your Camera’s Meter
I think one of the most confusing things for most beginning photographers is learning how to use the meter in your camera to set a proper exposure. The first images we take with a new camera are often our worst because each camera meters somewhat differently and the default metering mode for most is evaluative mode. This means that your camera is looking at the entire scene and averaging all the light and dark areas of the image. The light reflected back to the camera is read as 18% gray which is considered middle gray. To better understand what that means, let’s take a look at a process called the Zone System created by Ansel Adams and Fred Archer back in the early 1930’s.
Adams and Archer devised a method that would help to get consistent results between film and normal contrast photographic paper. In a very simplified version, they developed a scale from pure black to pure white and broke it into 10 zones. Zone 5 is middle gray, the same middle gray that your camera tries to convince you is the right exposure for all your pictures. Zone 1 would represent the pure black and Zone 10 is pure white.
The knowledge that your camera wants to make everything middle grey gives you the advantage to make white objects white and black objects black by adjusting from middle grey. Effectively, the camera is going to loose detail in the blacks at around Zone 3 and detail in the whites at around Zone 8. To make this information useful, average caucasian skin tone would fall at Zone 7. If your camera meters that skin tone as Zone 5, you will need to adjust your shutter speed, aperture, or ISO by 2 stops.
As an example, let’s say you meter directly off the person’s face and your meter says to set your camera at f/5.6 @ 1/125 with your ISO @ 100. In order to get a proper exposure, you would need to change your settings to f/2.8@ 1/125 or f/5.6@ 1/30. Both methods will put the person’s face in Zone 7 which will be a proper exposure. You could also change the ISO from 100 to 400 and accomplish the same thing. With any of the three changes, you are adding 2 stops of light on the subject and getting a more accurate exposure.
Try photographing a white wall using the camera meter settings and then take another shot opened up 3 stops. Which one gives you a white wall that still retains texture? The second shot, of course. The opposite can be used on a black wall. Close down 3 stops and the wall will be black without loss of texture.
Another method would be to meter off of an 18% gray card. Your exposure will be correct because the camera is seeing the same gray that it will always try to find. Gray cards are available at any camera store and are an invaluable tool. One caveat I would point out is that the light falling on the gray card has to be the same light falling on the subject in order for the exposure to be accurate.
In our next blog point, well discuss the differences between incident light meters and reflective meters. (Hint…the meter is your camera is reflective.)
I hope this will help understand metering better, but if you have any questions, please leave a comment below. I will answer all questions. Remember that the only stupid question is the one not asked.