Comparison Sigma 17-50mm f/2.8 AF OS HSM EX DC vs Canon 17-55mm f/2.8 EF-S IS USM

The system indicates which brand of cameras this lens is designed for. Manufacturers of photographic equipment often use original mounting systems in their cameras that are not always compatible with each other; therefore, for normal use, the lens must be originally designed for the corresponding system. At the same time, note that the actual compatibility will also depend on the mount (see "Bayonet (mount)"). At the same time, one system often includes several mounts (for example, Canon and Nikon); it happens vice versa — one mount can be used in several systems at once (for example, Micro 4/3 is used by both Olympus and Panasonic). In general, the optimal selection order is as follows: first clarify the compatibility of the lens with the system, then with a specific mount.

Also note that third-party manufacturers (who do not produce cameras and deal only with lenses) often produce models designed for several different systems at once. Such compatibility can be achieved both through a set of adapters (included in the package or sold separately), and through the release of different modifications of the same lens, differing only in mounts. The features of each such model should be specified separately.

The type of mount used to connect the lens to the camera. The name comes from the English "bayonet", meaning "bayonet" and a bayonet-type connection. Bayonet mounts are used in the vast majority of modern digital cameras due to their reliability and ease of use.

Full compatibility of the lens with the camera is guaranteed only if the types of their mounts match. Some mounts are compatible with each other via adapters, but such a connection can limit the capabilities of the lens (for example, it will make it impossible to use autofocus) and is generally not considered optimal. It is worth considering that within the same system (see above) different mounts are often used, which are also incompatible with each other.

So, the manufacturer Canon has mounts EF-M, EF-S, EF, RF, RF-S. Leica has Leica M, Leica SL, Leica TL. Nikon has Nikon 1, Nikon F, Nikon Z in its arsenal. Pentax optics are equipped with Pentax 645, Pentax K, Pentax Q. Samsung uses NX-M and NX mounts. Sony models include Sony A and Sony E. In addition, there are other types of mounts on the market - both branded ( Fujifilm G, Fujifilm X, Hasselblad H, Sigma SA) and universal ( Four Thirds (4/3), Micro 4/3).

Note that there are lenses that are declared compatible with several mounts at once. This “omnivorousness” can be realized in different ways. For example, some models have a non-standard mount on the lens body, and compatibility with various mounts is ensured through the use of adapters; These adapters can be included in the delivery set or purchased separately. Another option is that the lens is available in several separate modifications, each for its own mount. These details should be clarified before purchasing.

This parameter determines the size of the area of the scene being shot that falls into the frame. The wider the viewing angles, the larger the area the lens can capture in one shot. They are directly related to the focal length of the lens (see "Focal length"), and also depend on the size of the specific matrix with which the optics are used: for the same lens, the smaller the matrix, the smaller the viewing angles, and vice versa. On our website, in the characteristics of optics, viewing angles are usually indicated when used with the matrix for which the lens was originally designed (for more details, see "Matrix Size").

Minimum focus distance (m) - the smallest distance from which you can focus on an object and take a photo. Usually it ranges from 20 cm for wide-angle lenses to several metres for telephoto. In the macro mode of the camera or with the help of macro lenses, this distance can be less than 1 centimeter.

The degree of magnification of the object being shot when using a lens for macro shooting (that is, shooting small objects at the maximum possible approximation, when the distance to the subject is measured in millimetres). The degree of magnification in this case means the ratio of the size of the image of the object obtained on the matrix of the camera to the actual size of the object being shot. For example, with an object size of 15 mm and a magnification factor of 0.3, the image of this object on the matrix will have a size of 15x0.3=4.5 mm. With the same matrix size, the larger the magnification factor, the larger the image size of the object on the matrix, the more pixels fall on this object, respectively, the clearer the resulting image, the more details it can convey and the better the lens is suitable for macro photography. It is believed that in order to obtain macro shots of relatively acceptable quality, the magnification factor should be at least 0.25 – 0.3.

The number of elements (in fact, the number of lenses) included in the design of the lens, as well as the number of groups in which these elements are combined. Usually, the more elements provided in the design, the better the lens handles with distortions (aberrations) when light passes through it. On the other hand, numerous lenses increases the dimensions and weight of the optics, reduces light transmission (for more details, see "Aperture") and also puts forward increased requirements for the quality of processing, which affects the cost of the lens.