Third-party manufacturers make their lenses available in various mounts, these include Sigma, Tokina and Tamron.Įven when a camera and lens share a mount, it is possible that the lens is not suitable for the camera due to its sensor size. The Four-Thirds mounts is used for Olympus and Panasonic DSLRs and the smaller Micro Four-Thirds mount for their Mirrorless ILC (SLD) Olympus PEN E-P1 cameras. Sony actually has two, the Alpha for SLR Sony Alpha A700 and SLT Sony Alpha SLT-A55 cameras and the E for NEX Sony Alpha NEX-5 cameras. This goes for Canon, Nikon, Pentax, Samsung, Sigma and Sony. Most camera manufacturers have their own lens mounts. For a camera and lens to attach they have to have the same lens mount. This is also why wider apertures have smaller F/no.Ī mount is the connection between a camera and a lens. So, for a 100mm lens, an aperture of F/4 is 25mm across. TRIVIA Aperture is measured as a fraction of focal-length, shown as F/no. For the typical cropped-sensor DSLR, this is between F/11 and F/16. The point at which this happens depends on pixel size and is called the diffraction limit. This is rarely important because once a too small aperture is reached, the entire image becomes softer. Notice that lenses do not specify the smallest aperture on their markings. Below is a table explains the aperture range of some fictitious lenses. When there are two, the smaller number is the largest aperture at the wide-end of the zoom, while the larger is the largest aperture at the long-end of the zoom. This means that it can reach its maximum aperture regardless of focal-length. When there is only one, the lens is known as a constant-aperture zoom. Zoom lenses have either one or two maximum apertures. In almost all cases, a lens can be set to a much smaller aperture to obtain extensive depth-of-field.
Prime lenses only have one such aperture. Lenses are marked with the widest aperture they can be set to. The easiest is to remember that small numbers imply small depth-of-field and vice-versa. TIP Large apertures are indicated by small numbers, so F/2 is wider than F/8. Bright apertures are used to produce a shallow depth-of-field which causes background-blur. They are also often called fast apertures because more light allows for faster shutter-speeds. A wide aperture is also known as a bright aperture because it lets a lot of light in. Most times, the term aperture refers to the size of that opening. The row of images below shows the same subject shot from the same camera position but with different focal-length to illustrate how it affects the angle-of-view.Īn aperture is the opening inside a lens that lets light passes through. The narrower angle-of-view therefore lets you frame a smaller subject from a set distance. The longer the focal-length, the further you need to be to frame something of a specific size. The wider angle-of-view lets you frame a larger subject from a set distance. The wider the focal-length, the closer you can frame a specific subject. There are no official numbers, the table below shows the ranges used here and typical uses. Lens focal-lengths fall into broad categories according to the angle-of-view they give depending on the camera's sensor size. Short focal-lengths show a greater angle-of-view compared to longer ones. So a 150mm on a full-frame DSLR such as the Nikon D700 Nikon D700 gives the same angle-of-view as a 100mm on a D7000 Nikon D7000 since its FLM is 1.5X. The crop-factor, also called FLM Focal-Length Multipler, is the ratio representing the difference in equivalent focal-lengths. With a smaller sensor, the angle-of-view becomes smaller. With a full-frame sensor a lens gives the same angle-of-view as it would on a 35mm film camera. icon when searching for lenses by features to look for zoom or prime lenses.įocal-length determines the angle-of-view seen through a lens for a given sensor-size. TIP Enable the Zoom Lens or Fixed focal-length. So, while a 31mm prime Pentax FA 31mm F1.8 Limited always has a focal-length of 31mm, a 16 to 50mm Pentax DA* 16-50mm F2.8 ED AL (IF) SDM can be set to any focal-length between 16 and 50mm. A zoom lens can normally be set to any focal-length in its range, usually by turning a ring around its body. One that has a range of focals is called a zoom lens.
A lens with a single focal-length is called a prime lens. All lenses are primarily described by a single focal-length or a range of focal-lengths.
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