Camera Components and Concepts - Lens

The basic components of a DSLR are described below. (Most of the components in a rangefinder are also found in a DSLR.)

Lens, Aperture, Shutter, Digital image sensor, Memory card, External flash

Lens

A lens is a series of sophisticated elements, usually glass, constructed to refract and focus the reflective light from a scene at a specific point—the digital image sensor.
Beyond framing an image, the first interaction you have with the reflective light from your subject is through your camera’s lens.

Focal Length

An important attribute of a lens, besides its quality, is its focal length. Focal length is technically defined as the distance from the part of the optical path where the light rays converge to the point where the light rays passing through the lens are focused onto the image plane—or the digital image sensor. This distance is usually measured in millimeters. From a practical point of view, focal length can be thought of as the amount of magnification of the lens. The longer the focal length, the more the lens magnifies the scene. In addition to magnification, the focal length determines the perspective and compression of the scene.

Lens Types

Although there are many varieties of lenses, common lens types include telephoto, wideangle, zoom, and prime. All of these lenses perform the same basic function: they capture the reflective light from the subject and focus it on the image sensor. However, the way they transmit the light differs.

Note: Although there are several subcategories and hybrids of these lens types, these are the most basic.

Telephoto : A telephoto lens is a lens with a long focal length that magnifies the subject. Telephoto lenses are typically used by sports and nature photographers who shoot their subjects from great distances. Telephoto lenses are also used by photographers who want greater control over limiting the  depth of field (the area of an image in focus). The larger aperture settings, combined with the long focal lengths of telephoto lenses, can limit the depth of field to a small area (either the foreground, middle, or background of the image). Small aperture settings, combined with long focal lengths, make objects in

the foreground and background seem closer together.

Wide-Angle : A wide-angle lens is a lens with a short focal length that takes in a wide view. Wide angle lenses are typically used when the subject is in the extreme foreground and the photographer wants the background in focus as well. Traditionally, the focal length of a wide-angle lens is smaller than the image plane. However, in the digital photography age, the sizes of image sensors vary, and the lens multiplication factors of most DSLRs increase the focal length. Check the specifications of your camera to ascertain the size of your digital image sensor. If the size of your digital image sensor is 28 mm, you require a lens with a focal length less than 28 mm to achieve a wide-angle view.

Zoom : A zoom lens, also known as an optical zoom lens, has the mechanical capacity to change its focal length. A zoom lens can be extremely convenient, because many zoom lenses can change their focal lengths from wide-angle to standard and from standard to zoom. This eliminates the need to carry and change multiple lenses while shooting a subject or project. However, because of the movement  between focal lengths, the f-stops aren’t always entirely accurate. To achieve a greater level of accuracy with apertures, many manufacturers have multiple minimum aperture values as the lens moves from a shorter focal length to a longer one. This makes the lens slower at longer focal lengths. Plus, a zoom lens requires additional glass elements to correctly focus the light at different focal lengths. It is desirable to have the light pass through the least amount of glass in order to obtain the highest-quality image possible.

Prime : A prime lens also known as a fixed lens, has a fixed focal length that is not modifiable. Prime lenses often have wider maximum apertures, making them faster.  Wider apertures allow for brighter images in low-light situations, as well as greater control over depth of field. Prime lenses are primarily used by portrait photographers.