Understanding camera lenses can help add more creative control to digital photography. But choosing the right lens can be a task, with the varied options in cost, size, weight, lens speed and image quality. The primary characteristic of a lens is its focal length, which is the distance between the point of convergence of light in your lens to the digital sensor or film in your camera. In layman's terms, the focal length of your lens essentially determines how ‘zoomed in’ your photos are; the higher the number, the more zoomed your lens will be.
Regular lenses have a fixed focal length (50mm, 85mm, 100mm), and reproduce fairly accurately what the human eye sees, 50mm being considered standard. Lenses with a shorter focal length (10-42mm) enable a photographer to capture a wider view and are therefore called wide-angle lenses. They are best for capturing landscapes. Telephoto lenses (100mm - 800mm) provide a narrower field of view, compressing the distance) and can be used to take photos of objects father away, such as wildlife and sporting events.
Keep in mind that lenses will also affect your depth of field. As you zoom into a subject, your depth of field decreases.
