Comparison Sigma 18-35mm f/1.8 Art HSM DC vs Sigma 17-50mm f/2.8 AF OS HSM EX DC

General lens type. Note that this parameter is largely determined by the equivalent (not actual) focal length, but in the characteristics of optics, the actual value is most often indicated; see "Focal length" for more on this.

The type is not indicated for any optics, but only for models that have a pronounced specialization and clearly fit into a certain category. In addition to them, there are so-called universal lenses — see below about them. And specialized models can be of the following types:

— Fix. This category on our website includes almost all lenses that do not provide the ability to change the focal length. These can be wide-angle models, and optics with a long focal length, providing a high degree of magnification, and models with average values; the only exception is the ultra-wide-angle fisheye, which is a separate type (see below). Due to the simpler design, fixes are usually cheaper and more reliable than similar zoom models. Their main disadvantage is the actual constant focal length. Because of this, when working with fixes, you have to have your own lens for each type of shooting, and zooming in / out of the image is carried out solely by moving the camera closer / farther relative to the object being filmed (in professional jargon — “zoom with your feet”).

— Wide angle. Zoom lenses, the minimum value of which is up to 18 m...m inclusive, the maximum is up to 40 mm inclusive (both are in 35 mm equivalent). This provides a wide viewing angle with virtually no visible distortion (unlike ultra-wide-angle models, see below). "Wide angles" are often used for shooting landscapes, large objects, etc.; also, such a lens can be useful in tight conditions, where you need to capture the widest possible scene (for example, a large group of people), and the situation does not allow you to move far away.

— Ultra wide angle. Also, this type of lens is called fisheye, or "fisheye". Their equivalent focal length is up to 17 mm inclusive, and viewing angles can reach 180° and even more, which allows capturing a very large area of the surrounding space in one picture (for example, the sky around the entire circumference of the horizon). Such lenses have noticeable distortion in the resulting image: the centre of the frame looks closer than the edges, and straight lines that do not pass through the centre of the frame become crooked. Because of this, fisheye optics got their name: the view through it is similar to how a fish sees the ground from under the water. Most often, fisheyes have a fixed focal length, but there are also zoom lenses. Such lenses are used, in particular, to create panoramas, shooting in confined spaces, as well as to provide artistic effects.

— Tele. Lenses with a long focal length and, accordingly, a high degree of magnification, designed primarily for shooting at long distances. If we talk about specific numbers, then in our catalog telephoto lenses include models with a variable focal length, in which the lower limit of the focal length is at least 50 mm, and the upper limit is at least 200 mm. Such optics can be convenient, in particular, when shooting nature, sports competitions and mass events.

In addition to those described above, many lenses are produced that meet the criteria for several types at once or do not fit into any of them. Examples include, in particular, an intermediate option between wide-angle and telephoto lenses with a focal length of 24 to 55 mm, or a model with an extensive adjustment range like 28 – 200 mm, covering both of these types. Such lenses without specialization are called universal. In general, their scope is quite wide, and most of the optics supplied in the kit (kit) with SLR cameras belong to the mentioned “intermediate option”. However in terms of image quality, universal models are often inferior to specialized optics with a similar price; on the other hand, a set of several specialized lenses often costs more than a high-end "station wagon" with the same capabilities.

The general purpose is rather conditional, and in fact the use of optics is not limited to the claimed direction — it all depends on the skills and imagination of the photographer. However, information about the specialization can greatly facilitate the choice. Considering such original options as a cinema lens and a multifunctional.

— Architectural. Lenses designed primarily for shooting buildings. Most of these models are equipped with the Tilt-Shift system (see below). In this case, this function is intended to correct the perspective when shooting tall buildings. In a photograph taken with a normal lens, straight lines can turn out to be curved, which is unacceptable in cases where an accurate representation of the building in the picture is required. Using the Tilt-Shift system allows you to avoid this phenomenon and get a reliable image that does not require additional correction in a photo editor.

— Landscape. In this case, landscape lenses include short-focus (wide-angle) lenses, which, according to test results, provide good image sharpness. In other words, not all “wide-angles” are classified as landscapes, but only those that are actually capable of providing a clear, sharp image.

— Portrait. The hallmarks of a classic portrait lens are: first, the fixed focal le...ngth, which is usually over 50mm (35mm equiv.); secondly, high aperture (most often not lower than f / 2.8, although occasionally there are exceptions). This combination of characteristics allows you to shoot portraits with beautiful background blur, placing the camera at a fairly significant distance; the latter can be useful in studios where additional lighting equipment is used — it is advisable to install the camera behind lighting fixtures so that it does not give a shadow. Speaking of a fixed focal length, it is worth recalling that "fixes" are simpler, lighter and cheaper than zoom lenses, and the ability to adjust the magnification when shooting portraits is rarely required — most often you can completely get by with "zoom with your feet".

— Multifunctional. This direction includes lenses of a universal type (see above), offering the buyer a good value for money; in other words — multi-purpose models with good performance and at the same time relatively inexpensive (namely, "comparatively", the actual price can be quite high). When choosing models in this category, the quality of filming was evaluated according to the results of real tests.

— Film lens. The main feature of cinema lenses is the ability to fine-tune the aperture. The aperture can be closed / opened by 0.1 or even 0.01 mm, while in photo lenses the aperture setting step cannot be less than 1 mm. Additionally, in cinema lenses, aperture is expressed by a T-number, and in photographic lenses, an F-number is used. The operator can shoot multiple cinema lenses with the same aperture, without the need to change the lighting. And when using photo lenses with the same aperture, you often have to adjust the lighting for each optic separately. Cinema lenses are meant to be shot from a tripod, which is reflected in their design features and design — such models are usually larger and heavier than their counterparts for photography.

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.

Lens aperture is a characteristic that determines how much the lens attenuates the light flux passing through it. It depends on two main characteristics — the diameter of the active aperture of the lens and the focal length — and in the classical form is written as the ratio of the first to the second, while the diameter of the active aperture is taken as a unit: for example, 1 / 2.8. Often, when recording the characteristics of a lens, the unit is generally omitted, such a record looks, for example, like this: f / 1.8 or f/2.0. At the same time, the larger the number in the denominator, the smaller the aperture value: f / 4.0 lenses will produce a darker image than models with f / 1.4 aperture.

Zoom lenses usually have different aperture values for different focal lengths. In this case, the characteristics indicate two aperture values, for the minimum and maximum focal lengths, respectively, for example: f / 4.5-5.6

The larger the aperture of the lens, the shorter shutter speeds it allows you to use when shooting. This is especially important when shooting fast-moving subjects, shooting in low light, etc. And if necessary, the light stream transmitted by the lens can be weakened using a diaphragm (see below).

Another point that directly depends on this indicator is the depth o...f field (the depth of space that is in focus when shooting). The higher the aperture, the smaller the depth of field, and vice versa. Therefore, shooting with artistic background blur (bokeh) requires high-aperture optics, and for a large depth of field, you have to cover the aperture.

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").

Aperture is a design of several blades-curtains, which allows, if necessary, to reduce the diameter of the active aperture of the lens, actually reducing its aperture (for more details, see "Aperture"). In addition to reducing the light output (which can be relevant, for example, in bright sunlight), closing the aperture has another effect — it increases the depth of field. In other words, “in focus” is a larger volume of space than with an open aperture.

The values on the aperture scale are usually selected from a standard range. The numbers in it actually indicate what aperture the lens will have when the aperture is closed to a given value: for example, an aperture value of 5.6 will correspond to f / 5.6 aperture. The larger the number indicating the minimum aperture value, the more options the photographer has and, accordingly, the possibilities for setting the shooting mode (ceteris paribus).

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.

Lenses using the internal focus system. In such optics systems, focus is carried out only due to the movement of elements inside the lens body; the outer parts remain completely fixed and the size of the lens does not change. This provides additional convenience — in particular, it allows you to easily use petal hoods and those types of filters for which the correct position on the lens is important (in particular, gradient ones). In addition, the absence of moving elements from the outside has a positive effect on security and resistance to dust / precipitation (although the specific degree of dust and water protection may be different).

The presence in the lens of its own image stabilization system. Such a system includes gyroscopes and movable lenses that compensate for small tremors of the lens and prevent the appearance of “shake”. Stabilization is especially relevant when shooting handheld, especially at slow shutter speeds and/or at long distances with high magnification: it is in such conditions that “shake” affects the quality of the image the most. At the same time, it should be taken into account that the presence of a stabilizer significantly affects the weight, dimensions and, above all, the price of optics; at the same time, some modern cameras have their own stabilization systems (due to matrix shift). Therefore, it makes sense to choose a lens with this function in the case when maximum protection against “shake” is of fundamental importance.