Exposure, the Value of Control
Introduction to Exposure
This is the first of a series of articles on the basics of exposure in photography. The first will introduce the basic concepts of exposure and what influences you can control, the second will deal explicitly with aperture, the third with shutter speed (or duration of exposure), the fourth with ISO speed and then a fifth and final article to deal with utilizing these controls for artistic purposes.
In photography, setting the right exposure is fundamental. Its importance is eclipsed only by composition and the vast range of issues that it entails. Almost all of today's cameras have automatic controls which remove the worry about correct exposure from those photographers that are only interested in basic, usable photographs. However, many cameras still offer the photographer the ability to take control of exposure, either directly or indirectly, to improve upon the basic image and to make better photographs. If you set the camera on "Auto", then your photographs will typically end up correctly exposed for an average scene. However, if you have acquired a higher-end camera, especially digital, then usually you have a camera that presents extensive controls to you, the photographer.
Shooting on Automatic
What do you get when you shoot on Auto? Like I stated earlier, a correctly exposed photo for an average scene. Almost all automatic cameras try to convert the range of light and dark inherent in any image into an average tone. This works well in many situations but impedes any personal interpretation of the scene before you and basically takes the same photo for you as it would for anybody else using any other camera on auto. As photographers, we should always be attempting to master our unique style, our unique view of things, not just the average.
Exposure Controls
What exposure controls do we have? This depends on your camera. For some cameras, all you have is an on and off button. In this case, you cannot take any control, this really is point-and-shoot. On most cameras, at all price-points, you will have various modes typically identified as portrait, landscape, snow & sand and night. Using these settings will give you a "back-door" access to the main controls. On higher-end cameras, you will also have direct access to the controls of aperture, shutter speed and ISO speed. These three controls, when set in auto, all work together to try to obtain the correct exposure. By manually manipulating these, you can try to obtain the right exposure, right in terms of the mood and attention that you saw when you decided to take the photograph in the first place.
Specifically, the three controls are various ways of adjusting either the amount of light hitting the film or the sensor (if digital) or affecting the amount of light necessary for a good exposure. As an analogy, think of a gardener watering a planter. The aperture controls the diameter of the garden hose, the wider the aperture, the wider the garden hose, the more water (light) that flows through it in a given time period. The shutter speed is simply how long the gardener allows the water (light) to flow through the hose (lens), the longer the exposure, the more the volume of light. Finally, the ISO Speed is like the size of the planter, the bigger the planter, the more water it takes to fill it sufficiently. The lower the ISO Speed, the more light necessary to expose adequately. Increase any one, and you must decrease another to maintain the balance. With film cameras, changing the ISO Speed means changing the film which is not very convenient. However, with digital, it is usually just another setting that can be changed as the needs dictate. Gaining the right exposure is gaining the proper balance of these three influences to accomplish the the lighting mood desired.
Effects of Exposure Controls
What effect do these controls have other than simply exposing correctly? There are many that I will go into more detail in the next few tutorials in this series. However, I'll give you a few points to help put into perspective why the control is important.
Right Versus Correct Exposure
Canon EOS D60 digital SLR using F5.6 at 1/90 sec with an ISO setting of 400,
zoom lens at 28 mm
An example of a backlit scene
The adjustment of the overall amount of light is important depending on the subject matter. Shooting a snow-covered landscape, using the basic meter settings will result in dark, dirty looking snow, usually way too gray instead of bright white. A backlit portrait will have a fine exposure of the background, but usually the standard meter reading on auto will result in the face of your subject being too dark in deep shadow. Any scene with an extreme range of tones will not produce a good photograph if shot on auto. This is the difference between correct and right, it might be correct as far as the built-in meter is concerned, but it isn't the picture you intended to shoot.
Aperture
Canon EOS D60 digital SLR using F3.5 at 1/30 sec with an ISO setting of 100,
zoom lens at 28 mm
An example of a poor aperture choice
Aperture is how open or closed is the lens when taking the picture. Aperture affects Depth of Field for the photograph which, depending on the settings involved, can make a substantial difference to the resulting shot. Depth of Field refers to how much distance (from near to far) in you photograph is going to be in sharp focus. Those portraits of people or things where the subject is in sharp focus but the background is very blurred is as a result of setting aperture to control depth of field. Utilizing this can really make your photo stand out.
Shutter Speed
Canon EOS D60 digital SLR using F5.6 at 1/125 sec with an ISO setting of 400,
zoom lens at 112 mm
An example of a poor shutter speed choice
The length of time that the shutter is open will have a dramatic effect on your photo in several key ways. It will affect basic image quality and will also serve some artistic purposes as well. When hand-holding the camera, if the shutter is open for a long exposure, you increase the chance of camera shake. You also lose the ability of keeping moving subjects in sharp focus. However, this is sometimes a benefit such as shooting moving water where the blur of water motion will generally produce a more artistic, striking image giving the sense of motion and power.
ISO Speed
Canon EOS D60 digital SLR using F5.6 at 1/90 sec with an ISO setting of 100,
zoom lens at 28 mm
An example of a poor ISO Speed choice
This control serves the other two. By using a higher ISO Speed, you affect the combination of aperture and shutter speed by allowing for less exposure. However, a more direct affect will be the increase in the amount of image noise (for digital images) or grain (for film). Technology is still improving for both film and digital cameras in reducing the negative impacts of higher ISO Speed but there is still a visible impact. In the case of Digital, cameras using smaller sensors suffer very noticeably from even moderate ISO Speeds.
Summary
This tutorial has introduced you to the basic controls available and some of the impacts these controls have when manipulating exposure beyond auto, and why you would want to take control of exposure. Please be sure to read the subsequent tutorials in this series on exposure to gain a better appreciation of how you can benefit from taking your camera off automatic.
