Exposure: using a light meter

Now that we've talked about balancing shutter speed and aperature, totday's tutorial will help you figure out how to decide the exposure needs. A light meter is usually located inside the viewfinder of an SLR, but handheld meters can also be purchased. What you must remember is that a light meter can only measure the amount of light in the subject area, the determination of shutter speed/f-stop and the depth of field and action effects that those have, must be made by the photographer.


The actual method of integrated light meter will vary from manufacturer to manufacturer. There will be a light or needle displaying the needed amount of light for the scene and another indicator showing the amount of light allowed in with the current settings. By moving the aperature and shutter speed dials, you will see an instantaneous result of the exposure needs and can balance the "current" indicator with the "needed" indicator. For instance, you have an f-stop of 8 and a ss of 125, but the internal meter shows the number 500. You can either stop down the f-stop one position or increase the shutter speed one position. Either choice will reduce the light to the correct exposure, but you must choose whether you want the fast shutter speed to stop the action or the small f-stop for the greater depth of field.

A light meter works well in the average scenario, but there are instances when it can be easily fooled by the conditions. If the subject is much brighter or much darker than the immediate surroundings, then the meter will be thrown off. You have probably experienced this by taking a picture of someone standing directly in front of a window. The meter adjusted for the brightness of the window, and the person was underexposed. Since the light meter is clueless as to what you actually want to adjust for, there are several ways to deal with the problem.

1. Make a close-up reading of the subject. This way the meter is filled with the subject and will expose for it. be careful to ensure, though, that when you are doing this that you are metering on the object in the same light that it will be in when you step back to shoot. Also make certain that your shadow or the camera's shadow don't fall onto the area that you are metering.


2. Use the palm of your hand or a gray card if you are unable to get close to the subject (wildlife, a concert...) Again ensuring that you are using the same angle of light for your hand as for the subject, place your palm in front of the lens, then open 1 stop larger than the meter indicates. This is because the skin tone of the average palm is approximately twice as bright as the average subject. Instead, you can purchase a gray card from a photography store. So named because it is gray--18% reflected light which is what the average subject is. These are extremely useful but can be hard to tote around in a camera bag. The palm is great because it is always present.


3. If all else seems to fail, bracket. In instances where your hand cannot be in the same angle of light, and you cannot get close to the subject, first take the picture at the setting that the light meter recommends. Then take the picture 1 and 2 f-stops above and below the suggested settings.

Now that we've covered the basics, it's time to play! You definitely want to experiement a little bit before an important event. An instructor once told me to experiment with an orange as their dimpled texture will react very differently with different exposure settings. Have fun!

Exposure: balancing ss and aperature

Now that you understand the mechanics of ss and aperature, let's apply them! There are numerous different combinations of shutter speed and f-stops which will result in the same amount of light exposure. If you change to a faster shutter speed that lets in half as much light, then you could maintain the same amount of light by opening up the aperature one stop to allow back in half again the amount of light. The reverse is also true; if you change to a slower shutter speed that allows in twice the amount of light, maintain the exposure balance by using the smaller aperature opening to cut the light in half.

Now here's the twist: although changing the shutter speeds and aperature settings will maintain the same amount of light exposure, they will change the effects in the actual photograph. These effects will yield different values for depth of field as well as the ability to stop the subject's action (think freezing time).

Depth of field. Look at a picture and notice that the foreground is generally blurred, becomes sharper focused around the subject, and then grows gradually blurred again. This is referring to the depth of field. I'll cover this more in detail in a later lesson, but here's a good overview. The smaller aperature openings produce a larger depth of field while the larger aperature openings produce the shorter depth of fields.

Stop Action. When photographing a moving subject, you need to use a faster shutter speed, beginning with 500. Remember to use a larger aperature opening to maintain the correct exposure. You will not get as much depth of field this way, but at least the subject will be frozen in timeinstead of blurry from moving too quickly.

Application. Before taking your photograph, evaluate the subject and the setting. Obviously if you're at a NASCAR race, you don't want the photo to be blurry and will set a higher shutter speed (probably 1000). Just don't forget to open up the aterture for the correct exposure balance. The meter will tell you this (covered in another lesson), but never get into the habit of relying on your equipment to tell you what to do.

Exposure: understanding shutter speed and aperature

Rembering that pictures are actually representations of light will help you understand why balancing the amount of light is so important. Overexposure is the result of too much light being capture. The photograph will be washed out and indistinct. Underexposure is the result of not enough light. Images will be extremely dark. Optimum exposure will give you a photograph with rich colors and vivid details. The three main things to pay attention to (camera-wise) when setting exposure are:

1. Shutter speed (you might see camera literature refering to "ss")


2. Aperature (f-stop)


3. Light meter

In keep this lesson from being too long, I will cover the first two and save light metering for its own day.

1. The numbers on your dial represent the shutter speed--the length of time that the shutter opens to allow light to reach the film. They will read something like 1, 2, 4, 8, 15, 30, 60, 125, 250, 500, and 1000. (many newer, higher-end cameras will go even higher.) these numbers are actually not whole numbers, but are fractions of a second. Thus, 1 is a second. 2 is 1/2 of a second. 4 is 1/4 of a second. These number sound quite small, but are actually a long length of time to expose film to light on an average day. Each consecutive shutter speed lets in one-half the previous amount of light (more than or less than, depending on which way you're moving). Thus, 1/60 lets in twice as much light as does 1/30.

(Notice the subject is backlit--the light meter adjusted for the bright exterior with the result that the subject is underexposed.)

2. The lens will have a ring close to the camera body with more numbers stamped on it. These numbers correllate to the size of the aperature and will read something like: 22, 16, 11, 8, 5.6, 4, 2.8, and 1.4. (some lense will not have numbers all the way down to 1.4, but that's due to the mechanical properties of the particular lens.) The largest number corresponds to the smallest opening. This is, again, because they are fractions. Think of it this way: 1/22 is definitely smaller than 1/4. Simple! Just like the shutter speed functions, one f-stop is exactly one-half the amount of light as the previous f-stop. So, if you were using an f-stop of f/11 and needed to let in less light, f/8 would be axactly half the amount. Going from a larger aperature to a smaller on is called stopping-down.

Equipment: how a camera works

First of all, a camera is basically a box with a hole in the front that allows light to enter. The light rays are what form the actual image, or picture. Formerly, that light was captured onto film. Now that light is usually captured digitally and the results are stored on a memory card. Here are a few basic terms that relate to camera functions:

LENS--a glass piece that allows the light to enter the camera and also focuses the exact direction of the light. The lens sits in the hole in the front of the camera and is focused by rotating a ring on the lens (Pictured: the first ring with numbers on the lens).

APERTURE--the size of the hole and sits just behind the lens. The purpose of the aperture is to limit the exact amount of light entering the camera at any one time. The size of the aperture is changed by rotating a ring on the lens (Pictured:The ring closest to the camera).


HOT SHOE--a metal connection on the top of a camera that allows it to synchronize with a flash unit. Pictured in the top middle of the camera.

Also pictured on the left is an additional exposure dial, but since that is more advanced I will no cover it on this post.

SHUTTER--blocks the light from reaching the film until the you decide to take a picture (known as "exposing" the film). The shutter is inside the camera and can only be seen when the lens is removed. Shutter speed dial is the dial on the right of the camera, currently set to "P."

VIEWFINDER--designed to show the photographer what is being framed. Film cameras have a small box that the photographer must look through with one eye, while digital cameras usually have an LCD screen in addition to the traditional viewfinder.

SHUTTER RELEASE--the button that tells that camera to do its job.

Mirror shown in the down position where it normally rests. Shutter is closed.