Digital Photography may have eliminated many of the problems associated with film photography for the average user, but for those interested in serious photography or those interested in simply taking the best photographs they can, it's still important to understand the camera lens and use that knowledge to improve the quality of your photographs.
The camera lens has often been called "the camera's eye". It is the beginning of your photo. The lens gathers and focuses the light from your subject onto the sensor mechanism of your digital camera. The key elements are the quality of your lens, and how it handles the light.
Lenses vary in the amount of light they are capable of handling, the range in which they can focus, and zoom capability.
The main factor in the way your lens controls light is the aperture, which is simply the size of the opening through which light enters the camera. The bigger the opening the more light and vice versa. The aperture is varied by an adjustment that is measured in what are called f-stops. This adjustment allows you to compensate for different lighting situation in order to get the best results.
Remember that f-stops are measured so that the larger the number the smaller the aperture. They are divided by doublings. In other word an f2 allows twice as much light as an f4.
The second effect of f-stops is that they change your depth of focus. The smaller the aperture the greater your depth of field.
Aperture comes into play in several situations and your knowledge of it can change the nature of your photographs drastically. Here are a few examples of what can be done by changing the aperture.
By widening your aperture, you can eliminate background clutter. As an example, I recently went on a field trip with my daughter to a Historical Park, an old fort right outside of New Orleans. I had my daughter pose on a cannon which was on display in front of the fort. Because there was a rather large crowd of people milling around in the background, I chose a large aperture to take the picture. The result was a sharply focused image of my daughter on the cannon while the people and objects in the background were blurred and thus not a distraction that removed attention from the subject (my daughter).
Sometimes it's necessary to widen your aperture to get a good shot. Heavily backlit subjects tend to deceive a built in light meter, resulting in a subject that appears to dark in the final image. By overriding the automatic setting and increasing the aperture, the subject become visible in more detail. You may also wish to decrease aperture when photographing in highly reflective areas such as snow or water in order to avoid an overexposure.
Another consideration for your lens is close up photography. Since most people are using digital cameras for family snapshots and such, extreme closeups are not usually a consideration. However, if your creative nature occasionally compels you to take that great shot of the honeybee gathering nectar from a flower you'll need to give at least passing consideration to the range of focus of your lens.
Zoom lenses are an absolute must for the even semi-serious photographer. They allow you to get closer to your subject visually, even if distance or other limitations prevent you from getting closer physically. The range can vary widely with the least expensive lenses offering less range.
Zoom lenses are favorites of sports photographers and wildlife photographers for obvious reasons, but they also offer the casual photographer the ability to use the zoom feature for cropping out unwanted background features and honing in on the intended subject.