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Your camera is an important tool when it comes to finding the correct exposure of an image. However, we need to understand how it determines the amount of light hitting the film plane. Once you have the understanding of how your camera meter works you can manipulate exposures to better suit your purposes and correct for the instances when the meter is wrong. This article intends to inform any reader of the different types of light meters and camera modes used to evaluate light.

The first meters to concentrate on are the existing built in meters in the camera you already own. Depending upon the age and sophistication of the camera you are using it will have either a center weighted meter, matrix meter, spot meter or all of these above. Older cameras such as the Cannon AE-1 I learned on have a center weighted meter. The calculation of light is heavily influenced by the values in the center of the frame. The original thought was the subject would be centered so less importance was assigned on the fringes or even the power points of a composition. I have found that if the light is flat the center weighted meter can provide an accurate reading of exposure. But, if there is a great deal of contrast in the scene they can be quite inaccurate. I found that in sunrise shots with a center weighted meter taken without understanding the sky would be overexposed, foreground underexposed, and center just about right. For this reason I didn’t stop using the camera, I just use a different meter.

Matrix metering is the more advanced metering system installed by camera manufactures in modern SLRs. Although the terminology of different camera companies may refer to it as something else, the idea is the same. The frame is broken into quite a few sub-sections and all of the recorded light, except specular highlights, are averaged out. This metering system is much more reliable than the center weighted system. I found that it does a great job on the majority of lighting situations. The balance of values given to each section of the frame greatly enhances the speed of work and accuracy of the meter.

Some cameras with the matrix metering systems also include a built-in spot meter. This function will give a meter reading of only the small portion of the frame it is centered on. When trying to determine whether the contrast range is too great for your film or transparency, this is the meter to use. This is also the only meter that can provide an accurate basis for the zone system, which is still the most sophisticated exposure system developed. It is important to know that the “spot” can be a measurement of 1, 2, 5, or 10 degrees. The 1 degree spot meter is the best for its intended use. A 2 degree or sometimes 5 degree meter can be acceptable but I would not use the 10 degree. The intention of this meter is to get an extremely accurate reading of a small space. The larger the spot meter the less likely you will get only what you want to register. Even if you’re not using the zone system this is a great tool. In the situation that you are shooting a backlit subject, if you wanted to expose it correctly and blow out (overexpose) the background the spot meter evaluates what is necessary for the subject, set and shoot. This can be an effective technique for creative portraits or used in cases where the landscape has to many stops of contrast for your film. In that case, you can determine the exposure and shoot for the most important subject.

As for the built in exposure meters, the center weighted, matrix, and spot are going to be the primary choices in cameras today. However, if you want a bit more flexibility or need a meter for specific purposes such as studio work, a hand-held meter may fit your needs. There are two types of hand-held meters; the reflected light meter and the incident light meter. All of the built-in meters were in the class of reflective meters. A reflective meter is a meter that measures the light bouncing back from the subject. Normally, a hand-held reflective meter is just an independent spot meter. Again, my opinion is the smaller the spot (1 degree) the better. If you are typically a landscape photographer, this is the meter you want.

The reflective meters work in the same way as the built in light meter. Point it at the subject and it will give you a combination of f-stop and shutter speeds that will work. An incident light meter measures the amount of light falling on a subject. Place the meter in front of the subject, facing the camera, and read the combinations of f-stops and shutter speeds. More advanced meters today are offering both reflective and incident measurements. If you shoot a bit of everything this is the best bet. If you want to shoot subjects in a studio or controlled environment the incident meter is what you will rely upon the majority of the time. Once again, if you shoot landscapes, a dedicated spot meter is all you need.

With a reflective light meter, whether it is a spot, matrix, or center-weighted meter, there will be instances where the measurement will be wrong. To understand why, we need to look at what the meters are attempting to measure. All of these meters are designed to measure“middle gray.” The term middle gray refers to the absolute middle of the spectrum between white and black. Its density reflects at 18 percent and is the value that the camera meters have to match. So with subjects that are mostly lighter or darker than middle gray it will result in an underexposed or overexposed negative. As you photograph subjects it is important to understand that you can make the corrections necessary when needed. With a white subject it is important to open up and allow more light because the meters exposure will underexpose the subject matter. Likewise, when the subject is darker or black, the meters reading would underexpose the frame again because it reads it as gray.

From what I have found there are three easy ways to compensate for your meters weakness with light or dark subjects. The first is to use a gray card. A gray card can be purchased from photography supply stores inexpensively. The card reflects the 18 percent necessary for the camera to read. Put the card in the same light as the subject, take a meter reading and shoot the photograph ignoring the meter reading on the subject. The second option involves a natural gray card. In many circumstances you will not be able to put a gray card in the scene so metering off green grass or blue jeans has approximately the same reflective value. The third option is simply by knowing how much to compensate when in the situation. Do you open up one stop, one and a half, or more? If you complete this great exercise I learned at the RMSP summer intensive you can probably figure out how many stops you open up or close down depending upon the subject.

Metering modes have also changed with the modern cameras. When I consider which mode to use I need to understand what is important to capture the final image. First, let’s look at the options. There is a fully automatic option, aperture priority, shutter priority and the manual mode. In the fully automatic mode the camera takes the decision process out of your hands entirely. It uses the meters combination of f-stop and shutter speed and sets them automatically. I find that this is never a good option. In the fully automatic mode I can’t make the decision to blur the background of a portrait with a shallow depth of field. Or in a landscape the camera may select a shallow depth of field that takes quite a bit of the depth out of the image. You do not have the option to select what is important to you. In the aperture priority mode of your camera you choose the f-stop and the shutter speed is automatically set for you. In the situation where the critical decision revolves around depth of field this is the selection to use. The shutter priority mode allows you to choose the shutter speed and the f-stop is set automatically for you. The shutter priority and aperture priority are the modes I shoot from the majority of the time. I normally have my camera on a tripod, set the aperture or depth of field I want and let the speed falls where it may. Unless I want to slow water or another technique where again a tripod is necessary, set the shutter speed and let the aperture set automatically.

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