Understanding The Essentials Of Camera Lens

Lens Types

Prime lenses, also called fixed focal length lenses, have a fixed focal length and do not zoom. Their focal lengths generally range from wide-angle to short telephoto. Prime lenses tend to be sharper than zoom lenses since they have simpler optical constructions without zoom elements. They are also generally smaller and lighter than zooms. However, their fixed focal length means photographers need to change lenses to adjust compositions.

Zoom lenses have variable focal lengths, allowing photographers to change the framed area of a scene without moving closer or farther away. Their focal length ranges cover wide-angle to telephoto or telephoto to super telephoto. Zoom lenses offer flexibility but tend to be larger, heavier, and more expensive than prime lenses. Image quality may also not be as high in the entire zoom range compared to prime lenses. Popular zoom lenses include wide-angle, standard, telephoto, and super zoom lenses.

Lens Focal Length

Camera Lens  focal length is a key specification that determines the viewing angle and level of magnification. It is measured in millimeters and signifies the distance between the focal point at the center of the lens and the image sensor plane or film plane when the lens is focused on infinity.

Wide-angle lenses have focal lengths under 35mm and capture a wide scene. Standard lenses have focal lengths around 50mm, similar to human vision. Telephoto lenses have focal lengths over 70mm and provide increased magnification and a narrower field of view than standard lenses. Super telephoto lenses have very long focal lengths like 400mm or 600mm, providing high magnification for distant subjects.

Lens Aperture

The aperture of a lens refers to the opening which controls the amount of light reaching the camera sensor or film. It is measured in f-numbers, which are ratios of the focal length to the diameter of the entrance pupil.

Lower f-numbers like f/1.4, f/2, or f/2.8 indicate wider apertures that allow more light. Higher f-numbers like f/8, f/11, f/16 indicate narrower apertures. Wider apertures create shallower depth of field, gradually blurring out backgrounds and foregrounds from the point of focus. Narrower apertures produce greater depth of field with both foreground and background objects in focus.

Lens Quality Factors

Sharpness, distortion, and aberrations are some quality factors to consider when evaluating lenses:

Sharpness depends on precise optical design and construction quality. Lens sharpness is highest near the center and gradually decreases towards the edges of the frame, known as softening. Corner sharpness is important for wide-angle lenses.

Distortion causes straight lines to bend in photographs, most noticeably with wide-angle lenses. Barrel distortion bends outwards and pincushion bends inwards. High-quality lenses keep distortion low and often include profile correction in photographs.

Chromatic aberration causes color fringes along contrasty edges due to each color wavelength focusing slightly differently. Spherical aberration degrades image quality as lens elements are rarely perfectly spherical. High-end lenses have specialized elements to minimize aberrations across the frame.

Lens Mounts

Camera lenses need to be compatible with the lens mount of the camera body. Different lens mounts exist across camera systems:

- Canon EF mount is used on Canon DSLRs and mirrorless cameras.

- Nikon F mount is used on Nikon DSLRs, with the new Z mount for mirrorless bodies.

- Sony E-mount is found on Sony mirrorless interchangeable lens cameras.

- Four thirds mount is used on Panasonic and Olympus mid-range DSLRs and mirrorless cameras.

- L-mount is the standard for Leica, Panasonic, and Sigma full-frame mirrorless systems.

Camera lenses cannot be swapped freely between systems without mounting adapters. Matching lenses to camera mounts is important for full compatibility.

Choosing Camera Lenses