In Chapter One I gave you an overview of your camera’s light meter—how it functions and how you can use it in Manual mode to guide you in choosing settings that will yield a correct exposure.
Now that you are gaining more control of your DSLR by utilizing the Scene modes and P mode, it’s time to expand our discussion of the light meter.
How does the camera evaluate the scene and determine a proper exposure? It uses what are called the Metering modes, also known as the Light Metering modes.
DSLRs are set to this mode by default and it’s used most of the time. The camera evaluates the entire scene and picks an exposure that will work well. It will link to any AF (autofocus) point you choose.
These modes are useful when you want the camera to accurately expose one part of a scene. Let’s say you are taking a photo of someone with rich, golden backlighting behind her. If you use Evaluative Metering mode, the camera will evaluate the entire scene and most likely darken the subject’s face. If you use either Partial Metering mode or Spot Metering mode, the camera will take its reading from the subject and maintain correct exposure of the subject despite the backlighting. Tips: (1) Spot Metering mode gives a bit more control than Partial Metering mode. (2) Some DSLR’s Spot/Partial metering modes function only at the center of the viewfinder. For those DSLRs (which include the less pricey Canons), you will either have to use these modes with the center AF (autofocus) point or utilize the AE lock button to lock exposure while using an AF point other than the center one. If using Manual mode, you will have to meter using the center of your viewfinder. All Nikons and pricey Canons can spot meter off any AF point. Sound Greek? No worries, as we’ll discuss AF points and AE lock later in this chapter.
This mode is a combination of Evaluative and Partial/Spot Metering modes and is the least used. It evaluates the entire scene, giving priority to the frame’s center.
This photo was taken during the evening, with rich, golden natural backlighting and subtle top lighting. Spot metering was used to ensure that the subject’s face would be properly exposed despite the backlighting. 15–85mm f/3.5–5.6 lens at 67mm, ISO 200, f/5.6 for 1⁄60 sec.
Your camera’s internal light meter is not perfect—exposure compensation to the rescue!
Your DSLR’s internal light meter is calibrated to measure reflected light as opposed to the actual light that falls on the scene (called incident light). It is programmed to average out the light and dark tones in your scene and give you an average reading of 18 percent gray. This creates a well-exposed photo most of the time, except in cases where you have either a lot of white tones in the scene or a lot of black tones. In these cases, the camera will still average the tones out to 18 percent gray.
What does this look like in your photos? In scenes with a lot of black, the black tones will look dark gray. In scenes with a lot of white, the white tones will look gray. These toning problems can easily be corrected with exposure compensation—overriding the camera’s setting selections to either increase or decrease your exposure.
If you choose the exposure compensation feature and turn the dial to the right, you increase exposure. If you turn the dial to the left, you decrease exposure. Note that exposure compensation can be used only in P mode, Aperture Priority mode and Shutter Priority mode. (In Manual mode, you decrease or increase exposure by dialing in settings for aperture, shutter speed and ISO.)
A general rule of thumb in using exposure compensation: For scenes with a lot of black tones, decrease exposure by one to two full stops. For scenes with a lot of white tones, increase exposure by one to two full stops.
Some photographers use external light meters, which measure actual light that falls on the scene (incident light) as opposed to light that is reflected off the elements in the scene. These handheld meters are more accurate. There are several light meter apps available, all of which get mixed reviews. They are much cheaper than actual external light meters and might be worth a try, especially if you are not shooting in a studio situation. Try the app Pocket Light Meter.
In this snow scene there is obviously a preponderance of white. In averaging out these tones to 18 percent gray, my camera indicated a “correct” exposure, which you can see turned out rather gray. I used exposure compensation to increase exposure by two full stops, which resulted in the bright white snow that I saw with my naked eye.