Jay Sousa: The basics of light meter

August 22, 2013 

Exposure is at the very core of making a good image.

If our exposure is off, our images will be either too dark — underexposed — or too light — overexposed. A correct exposure is crucial to let the viewer see all of the detail that is in a scene.

A correct exposure is vital with photographs of people, as an overexposed image will make it very difficult to render skin tones correctly. I fear that some new photographers don't take making a perfect exposure seriously and just rely on "fixing" the image in post-processing after the fact.

It is true that you can make a bad exposure better by using photo-editing software, but if your exposure is way off the mark you will never make it perfect. Another reason to learn to make good exposures is the pride that you will feel in mastering the craft of photography.

Before we can learn how to make a good exposure, we need to understand a little about how light meters in modern DSLR cameras work.

Most modern DSLR cameras have several different metering modes that analyze the light that is reflected off of your subject as it passes into your camera. It is important to remember that the camera measures reflected light off of your subject not the light that falls on your subject.

DSLR cameras have two basic ways in which you can use your light meter.

The first is putting your camera on one of the automatic modes. These auto modes let the light meter make an exposure based on the light that the meter reads.

The second method is to set your camera on manual mode. In this mode the light meter evaluates the brightness of the scene but you, the photographer, based on what the meter tells you, sets the correct aperture and shutter speed to make an exposure and render the photograph the way you want it to be seen.

The problem with light meters that we need to understand is that they do not know what is important to you in the image that you are making.

For example, a common exposure problem for me as a wedding photographer is a bride in her beautiful white wedding gown and the groom in a black tuxedo outside on a bright sunny day. The white wedding dress reflects a lot more light than does the groom's black tux.

A light meter set on one of the basic metering modes tries to make a scene middle gray and will set an exposure based on middle gray.

In the situation with the bridal couple, the meter measures all of the reflected light from the wedding dress and is fooled. The result is an underexposed image in this case. This photo would leave the wedding dress an ugly gray when it should be a crisp white.

I would combat this problem by making sure that I had the meter set on manual mode. This way I could make adjustments to the exposure based on the way I want the image to look.

In the wedding photo example, I would analyze the exposure data and then set my exposure a stop over what the meter is telling me. This way, the wedding dress is now exposed properly and is white and the black tux now has detail, making for a much more pleasing image.

The most important thing to remember is that the meter is just a tool. You, as a photographer, need to analyze what it is telling you. After visualizing an image the way you want it to look, use the tools that you have to make that image happen.

In my next column, I will be looking at some of the other metering modes that you can use to fine-tune your images.

For anyone wanting a more comprehensive look at exposure, I will be teaching a short-term class through Merced College Community Services titled "Understanding Your Digital Camera." This class runs three consecutive Saturdays starting Sept. 14 from 9 a.m. to noon. Contact the community services office at (209) 384-6224 for more information.

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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