The focal length of the camera lens is one of many features that affect the final photo. The focal length determines how close a photographer can be to the subject and still fit them in the frame. Generally, lenses with larger focal lengths will be longer, but there are exceptions to this.
Importance of Focal Length
Wide-angle lenses are useful to photographers because they allow the photographer to get close to their subjects and to fit more into the picture. These lenses are useful for taking pictures of large groups of people or in confined spaces. Telephoto lenses allow the photographer to take pictures of objects that are far away. These are especially useful for sporting events and wildlife where the photographer cannot get close to the subjects. When using telephoto lenses, faster shutter speeds must be used to avoid blurring from the shaking caused by snapping the shutter. Focal length also affect the composition of the photo. With a wide angle lens, objects will look farther apart while a telephoto lens will compress objects so they appear closer together.
Zoom Lenses
Zoom lenses are lenses that cover a range of focal lengths rather than having just one focal length. These ranges can be as small as 10-22 or wider than 28-200. Zoom lenses with focal lengths smaller than 35 are referred to as wide angle. Lenses from 35-70 are normal. Lenses from 70-135 are medium telephoto and anything larger than 135 are telephoto lenses. The advantage of zoom lenses is that they can cover multiple focal lengths and reduce the need for a photographer to change lenses.
Fixed Focal Length Lenses
Some lenses have only one focal length. These lenses force the photographer to move around to change the composition of the photo rather than changing the zoom. These lenses are usually faster, sharper, and smaller than zoom lenses which is why some high-end photographers prefer them to zoom lenses. Faster refers to the fact that shorter exposures are required so they can capture moving objects without blurring. Sharper refers to the quality of the final photo.
Field of View Crop Factor
With some digital cameras, the senors are not big enough to capture an entire image the same way a film camera does. Since the sensor is smaller, less of the image makes it on to the senor and the remaining image is enlarged. Common crop factors are 1.3x and 1.6x.
Fun Fact
The largest focal length is 1700mm on a Carl Zeiss lens.
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