This is a manual for a Camera Lens:

Also known as: Photographic lens, Objective Lens, Photographic Objective. Definition: A camera lens is a combination of curved pieces of glass and is used to focus images on a photographic film or a camera’s sensor. A camera lens has two important specifications – the lens opening and focal length. The lens opening (also known as f-stop) determines the amount of light that enters the lens. This aspect is controlled by the camera’s shutter speed and aperture. The focal length determines the amount of magnification and the angle viewed by the camera. For example, a wide-angle camera lens has a larger focal length, compared to a normal lens. This enables the former to increase the viewing area. Objects in an image taken by a wide-angle camera appear smaller than what they would appear in images taken by a normal camera lens. Focal length is expressed in millimeters (mm); usually, a normal lens used in a digital camera has a focal length of 32mm. In an SLR camera, the lens may be changed according to the image attributes required by the photographer.

Sony Description of SAL100M28 SAL100M28

Get incredibly close to small subjects with the Sony SAL-100M28 macro lens. Its superb clarity gives you professional results in almost any shooting situation. The superb macro-focus lens for both close-up and distant subjects. This versatile macro-focus lens covers a wide range of photographic applications, from close-up nature subjects to midrange telephoto shots - making it ideal to carry on location or in the field. It provides a 150mm focal length (35mm equivalent) - and its superb sharpness and clarity give you professional results in every shooting situation.