The job of the camera lens is to bend the light. This may sound strange, or even impossible, but this is accomplished by regulating the speed of the light. All lenses are really curved pieces of glass (some are plastic, but the quality lenses are made of glass). Light travels faster through the air than it dose through glass, so as it hits the glass it slows down. Some portions of the light hitting the glass sooner than the rest cause the bend in the light. The first part of the light slows as it passes through the glass, while the light that hasn't reached the glass is still traveling at full speed. This causes the light to bend. The curve of the camera lens will determine how much of the focal plane is captured.
Camera Lens Types
Normal
The focal length of this camera lens is measured in millimeters and determines the lens's viewing angle. Camera lenses with a 35mm - 105mm viewing angle are called normal lenses. These camera lenses have a wide range of use and are very popular.
Zoom
Zoom lenses let you change the focal length of the lens, a 4X zoom will magnify a scene by four times compared to it's wide angle setting. This optical zoom is much more important as compared to digital zoom which makes images appear to be bigger by enlarging the pixels that have already been captured i.e. no new information is actually added and if you zoom in too much the image becomes pixelated.
Wide Angle
Wide-angle camera lenses are excellent for capturing large scenes or big groups of people. They are not as good for close-up portraiture, as they tend to distort the subject. Tilting a wide-angle up or down creates converging or diverging lines out of lines that are parallel. Also, people's heads at the edge of a wide-angle frame can be very distorted. Wide-angles are great for shooting architectural interiors (watching out for those converging/diverging lines) as they give a wonderful sense of space.
NOTE: With add on wide angle lenses most compact cameras suffer from the flash being obstructed by the lens itself and a shadow will appear in the picture where the lens blocks the flash light. It is best note that this can occur and to check before purchasing.
Telephoto
Telephoto lenses bring your subject closer to you. Because they also magnify camera shake they can be a problem, producing blurred pictures, therefore a tripod is recommended. Although they are usually heavy and bulky some have integrated optical stabilization combating some of the shake, telephoto lenses are ideal for use in many situations. Telephotos not only get you close to faraway subjects, they also compress foreground and background and have an inherently shallow depth of field. Moderate (85 to 200mm) lenses are great for portraiture. Such lenses flatter most peoples' faces and blur backgrounds, thus helping to focus on the subject. Large (300mm and up) telephoto lenses are a must for sports and wildlife photography.
Teleconvertor Lens
By adding a teleconvertor lens to your existing camera lens you can bring your subject closer by 2 to 3-times magnification. This lens addition increases the focal length of your standard camera lens, normally used on compact cameras with an add-on facility.
