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Proper exposure is critical to a photograph such as this image with foreground interest (the boat) and a colorful background including the the setting sun. Leaving the camera on automatic will underexpose the image due to the presence of a bright light source (the sun). Putting the camera on manual and setting the exposure results in a better image.

Come on, admit it! Most, if not all, of the pictures you take are with the camera on automatic, you know, the green 'idiot box.' on the camera dial. You think you are are allowing the camera to make the 'right' decisions for you about everything but composition. In fact, someday cameras might have the capability to warn us of bad composition. “Warning, Warning, please move two steps to your left for a better picture!' says the camera. OK, maybe not. But until then, it is necessary to take control of the camera and make decisions yourself, using the camera as a guide. This is most important when it comes to proper exposure.

What is proper exposure? To me, proper exposure creates a photograph matching the photographers vision. That may seem vague, but it is true. As a photographer you are in charge of applying your vision to a scene. The art of determining exposure accomplishes that. The technical implementation, or skill, of determining exposure involves the proper selection of aperture, shutter, and film speed.

In this, and future, columns I use the term film plane. Since readers may be using either film or digital cameras, the term is used to indicate the exposed image on either film or a digital sensor. All concepts and definitions apply equally to both.

Film Speed (ISO): The ISO number of film is the relative measure of the films sensitivity to light. The lower the ISO value, the less sensitive the film is to light. The higher the ISO, the more sensitive the film is to light. For example, film with an ISO rating of 100 is ½ as sensitive to light as film with an ISO rating of 200. In other words, ISO 100 film needs more light (twice as much) then ISO 200 film to obtain an equivalent exposure.

Aperture: The aperture is represented by the numbers, such as, 2.8, 4.0, 5.6, 8, 11, and so on that are printed on the barrel of your camera lens. Aperture controls the amount of light striking the film plane.

Shutter Speed: The shutter speed determines the length of time that a measured amount of light strikes the film plane. The numbers, ½, ¼, 1/8, 1/15, 1/30, 1/60, 1/125 etc represent fractions of a second and indicates the length of time the shutter is open.

To summarize, Exposure is a measured amount of light striking the film plane for a given amount of time. When done correctly, the resulting exposure is not too dark (underexposed), not too light (overexposed), but just right matching the vision of the photographer.

If you wish to take photographs instead of snapshots, you're going to have to move that dial off the green 'idiot box.' We'll continue to explore issues of exposure in columns to come. Until then, keep shooting.