Camera Lens – Get the best ones always for clarity.
In layman terms, a lens is simply a piece of glass that can be used to focus light on to a point. Transparent materials are used in manufacturing of lenses. Glass due to its good optical and resistance properties is the most widely used. Nowadays, various plastics such as acrylics are also being used in manufacturing of lenses. The low-cost disposable cameras are often fitted with molded plastic lenses. Each camera has an aperture (hole or an opening) that allows light to pass through. To regulate the amount of light needed the camera is equipped with an iris diaphragm. The role of the diaphragm is to allow light to pass only through the aperture. Lenses "Focal Length" and "Aperture" are the two technical specifications that would be of interest to any photographer. In other words, focal length is the distance from the lens to the point of focus when the lens is focused on infinity. Focal lengths are usually measured in millimeters (mm). In older times the lenses used to marked in centimeters (cm) and inches (in). For a given film or sensor size, the lens can be classified into three categories viz. normal lens, wide-angle lens and telephoto lens.
Normal Lens: For a 35 mm film, when the focal length is 60 mm, the image formed will look normal, as things appear to naked human eye. The appearance of the depth or space between objects will look normal with a normal lens. Objects close to the camera look larger and much closer than they really are and vice-versa.
Telephoto Lens: As focal length gets greater than 50 mm, the angle of view becomes narrower. Thus, the telephoto lens captures a small portion of the object in focus while making it much larger in appearance.
In simple terms, "aperture" is the size of the opening in the lens. The aperture affects the depth of focus on our subject. Larger the focal length, larger should be the opening in the aperture in order to let in ample light to expose the image. to correct the light-spread a special type of calculation called f-stop is used. This calculation involves the dividing of opening to the focal-length. Thus, the larger the f-stop the smaller the actual opening on the lens.