Jay Sousa: Learn to use a light meter, its modes

August 31, 2013 

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The Nikon D3000, a 10.2-megapixel DSLR, is the perfect entry-level camera for those who want something more powerful than a simple point-and-shoot. (Nikon/MCT)

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The light meter in a modern DSLR camera is a sophisticated tool. However, many photographers believe that the camera meter is designed to choose the perfect exposure for every photo, every time. Unfortunately, this is not the case.

The meter just reads how much reflected light is hitting it from the scene the camera is pointed at. It is calibrated to give an exposure that will make the scene it sees middle gray, which for most lighting situations and subject matter will make an acceptable image.

One exception to this is with contrasty light and-or subject matter. The bride, whom I cited in my last column, in her white dress and the groom in a black tuxedo outside on a sunny day is a prime example of this.

Camera manufacturers have developed sophisticated metering modes to help with making a good exposure in difficult lighting situations. Typically, these different metering modes are based on the meter reading multiple sensing points across the entire image area. The camera reads the light at these points and then compares them with algorithms to give an exposure.

These multipoint systems go by names like evaluative, center-weighted, partial metering or spot metering. These are the names given for my Canon 5dMKII metering modes. Other camera manufacturers might have different names. Nikon, for example, uses evaluative matrix. If you're not sure, refer to your camera manual.

So when do you use these different modes? Let's break them down and see the best use for each one. The first thing that you will have to do is refer to your camera manual and learn how to quickly, and easily change from one mode to another.

Let's start with the evaluative mode. In this mode the camera takes into consideration everything in your frame. Most cameras will have numerous metering zones around the frame (for example, the Canon 5D has 35 points that it reads).

It assesses overall lighting from all these zones and suggests an exposure based by averaging them to decide on how to expose the shot. This mode gives great results in most lighting situations where the light is even and the values (highlights and shadows) are not too far apart.

The next mode is the center-weighted mode. In center-weighted metering the camera will take information from numerous metering points around the frame but will give more weight to those in the center. This is a good choice for portraits, as we normally place our subjects in the middle of the frame where the majority of the light will be measured from.

One good tactic when using center-weighted mode is to move in close to your subject matter and have the light meter measure the light on the part of the image that you want exposed correctly, such as someone's face. After you set the exposure, back up, recompose and then make your image. My camera is set on center-weighted mode about 70 percent of the time.

The next two useful modes are partial and spot metering modes. In these modes the camera reads the light from a very small spot in the middle of the viewfinder instead of taking information from all of zones. You can set the meter to read 8 percent of the scene, which on my camera is the partial mode or just a tiny 3½ percent of the total scene; this is the spot mode.

This is a very useful mode for tricky lighting conditions, where the whole scene is either darker or lighter than the point that you want to be exposed correctly. I would use the spot meter mode for landscape images where, for example, I want to make a perfect exposure of just a bit of light that is striking a mountain.

Another good use of spot metering is in a backlit situation, where you're taking a portrait of someone who is in front of a bright scene. Without spot metering in this situation you might end up with a silhouette and you might not be able to make out the features of your subject.

Editor's Note: This is the last in a series Jay Sousa, a former Sun-Star photographer, has his own photography business in Merced, conducts private classes and teaches photography at Merced College.

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