Types of lenses. Lens field of view

Field of view (field of view)   called the part of the space of objects, which is visible or depicted using this optical system. The field of view of optical systems is usually characterized in the angular measure. So, considering any subject, we judge its size by the angle under which it is visible. The angle of view of the lens is understood as the solid angle (conic) angle formed by the lines connecting the front main point of the lens with the edges of the imaged space. Express the angle of view of the magnitude of the flat angle, the rotation of which forms this conical angle.

The image given by the lens does not have the same quality across the entire field; the sharpness and brightness of the image are most pronounced in the center of the field. As the distance from the center increases, the sharpness and illumination are noticeably reduced, and at the borders of the field the image is very vague and dull. So on the image obtained using a simple lens, the boundaries of the field of view cannot even be set due to a significant loss of sharpness and lightness to the edges of the field.

The central part of the field of view of the lens, within which the image has a degree of sharpness sufficient for photographic purposes and which is actually used in the photo system to obtain an image on a photosensitive material, is called image field   lens. The size of the image field determines the frame size. The diagonal of the frame is equal to the diameter of the image field.

The angle formed by the rays connecting the extreme points of the image field with the rear main point of the lens is called image angle   Lens β:

where d   - diagonal frame f    - focal length.

The field of view is limited by the field diaphragm, which usually has the shape of a circle in observation devices (binoculars) and a rectangular shape in cameras. The size of the field diaphragm is determined by the size of the sharp and sufficiently illuminated image, which is noticeably undegraded by aberrations, suitable for practical purposes.

Fig. Field of view

Fig. Angle of view and image circle 24 * 36 mm

Lens classification bycorner image

Depending on the ratio of the diagonal of the frame and the focal length of the lens, the following main types of lenses are distinguished:

normal-angle lens, whose focal length is approximately equal to the diagonal of the frame;

narrow-angle - the lens, whose focal length significantly exceeds the diagonal of the frame, has a small angle of image and is intended for shooting distant objects;

wide-angle lens, in which the focal length is noticeably shorter than the diagonal of the frame; designed for shooting in a limited space;

ultra wide angle lens (“fisheye”) - a lens whose image angle is more than 140 ° or even 180 °. It has very large geometric distortions and is mainly used for artistic photography.

variable focal length lens, the so-called zoom lens (sometimes also called zoom lens, or simply zoom).

5. The resolution of the lens.

Resolution is the ability of the optical system to represent two lines or points separately, characterized by the maximum number of transparent and opaque strokes equal in width, distinguishable by 1 mm of the image length. Determined by special bar tests:

visually - by examining the optical image of the line world constructed by the lens on an optical bench into a microscope, without photographing it on film, the value obtained is called resolving powerlens.

photographically - photographing the dough. When analyzing the resulting image, use the term " photographic resolution".

The magnitude of the resolving power is determined by a number of factors: 1) light diffractionon the round holes of the frames in which lenses and other components of the lens are mounted; 2) residual aberration   errorsoptical lens system; 3) lens scattering; 4) worlds contrast.

The resolution power of the lenses is not uniform over the image field,the central beams, reaching near the main optical axis perpendicular to the film plane, provide the highest resolution. The image at the edges of the image is built with oblique rays and has a lower resolution due to the presence of lens aberrations, which are always greater at the edges than in the center.

Time decisive force is maximumat a certain value of the relative aperture (diaphragm).

A standard or conventional lens is a lens whose viewing angle coincides with the viewing angle of the human eye without lateral vision. The focal length of such a lens is approximately equal to the diagonal of the frame. Almost always, such lenses have a high aperture ratio (this is characterized by value), which allows taking photographs with relatively short shutter speeds in low light conditions.

Wide angle lens

Wide-angle lenses cover more than the standard angle. The smaller the focal length of the lens, the greater its viewing angle. A lens with a focal length of 20 millimeters (for a 35-millimeter camera) “sees” diagonally about 90 degrees of space. All lenses with focal lengths from 20 to 50 mm can be called wide-angle.

Super Wide Angle Lens

Super wide-angle lenses are focal lenses from 14 to 20 millimeters. They can be divided into two groups. These are direct lenses that allow you to get images either without distortion, or with an acceptable level of perspective distortion, and distortion, giving barrel distortion. Distortion lenses are called “fisheye” (the name originated from the visual similarity of the front lens of the lens and the fish eye).

Fisheye lenses are of two types: with a field of view of 180 degrees on the diagonal of the frame (16 mm) and 180 degrees on the vertical frame (8 mm). With the help of "fish eye" you can get the original effect and a kind of expressiveness. Ultra wide lenses are used in reportage, architectural, interior and landscape photography.

Long lens

Long-focus lenses “bring closer” to the photographer's subject. They can also be divided into two types: telephoto and telephoto lenses. They differ structurally. In telephoto lenses a negative lens has been added, thanks to which manufacturers have achieved a significant reduction in overall dimensions. If we compare two lenses of the same focal length, the telephoto lens will be significantly smaller in size and weight. But it was the custom that telephones (telephoto lenses) called all approximating lenses.

Extra long focus lens

These are lenses with a focal length of 500 millimeters and more. There are lenses with a focal length of 2000 mm, but this is already a rarity. The weight of such lenses is more than 6 kilograms and shooting on them without a tripod is almost impossible. Almost all of them are equipped with a special tripod mount. Constructive type of super long focus lenses - mirror-lens. In this design, spherical mirrors perform part of the optical structure. This design significantly reduces the weight and size of the lens, but not without its drawbacks. Unfortunately, in such lenses it is impossible to install a changing aperture, which means that the exposure will have to be adjusted only by shutter speed and photosensitivity. The light-tonal pattern of such lenses is extraordinarily beautiful, it is almost impossible to repeat it with any other lens. Also, this design is found in many amateur telescopes.

Zoom lens

So called lenses with variable focal length. Modern manufacturers can please you with a huge assortment of lenses of this type. Such lenses are really convenient: one such lens can replace several. You can more accurately build a composition, significantly increase the efficiency of work, for example, in wedding photography or sports photography. But not everything is as good as it seems at first glance.

Zoom lenses have flaws. Short-focus zoom lenses suffer from distortion, and the shorter the focal length (the larger the field of view), the greater the distortion. By the luminosity of such lenses are divided into two categories: with a constant and variable aperture. In the case of a variable aperture, the aperture varies with the change in focal length. For example, the lens 28-70 with a focal length of 28 mm aperture value (aperture) - 2.8, and at 70 mm - 4. This degrades usability. In such lenses, the aperture is smaller, the greater the focal length. Lens with constant aperture do not have such flaws. As they say, you have to pay for everything in the world, and for the constant aperture of zoom lenses. They, as a rule, are 1.5-2 times more expensive than with a variable aperture.

Soft lens

A soft focus lens or soft lens is usually available with a set of removable apertures. In such a diaphragm, the central opening (equal to a non-specific working diaphragm) is surrounded by many smaller openings. The central hole creates a sharp image, while the outer, smaller ones dissipate it. The dispersion level can be adjusted by replacing the insertion diaphragm. This makes it possible to significantly change the effect of soft focus and the degree of dispersion. In some models, spherical aberration is not specially corrected.

Macro lens

A lens that allows you to shoot without special devices on a 1: 1 scale. Such lenses, unlike all the others, are corrected when shooting at a finite distance aberration.

Shift lens

The name comes from the English word Shift (“Shift”), with the help of such a lens, you can get rid of perspective distortions by shifting the lens unit parallel to the film or matrix plane. This is the main lens for those who want to shoot, cityscapes or still lifes without distorting the perspective. When shooting, the camera is positioned so that the optical axis of the lens is parallel to the ground. When shooting from the bottom up, it is necessary, moving the lens unit, to make sure that the upper parts of the objects enter the frame. Accordingly, when shooting from top to bottom - on the contrary.

Of course, there is a constructive limit for such a shift. And not always, for example, because of the height of buildings, it is possible to get rid of distortions. At the very least, perspective distortions will be minimal. The cost of shift lenses is higher than that of conventional wide-angle lenses of the same focal length. In image processing programs (for example, in Photoshop) there are possibilities to simulate correction of perspective distortions. Why imitation, because in a real shoot a different perspective effect is created. Sometimes this fix is ​​noticeable. It is important to remember that with computer-aided correction of the distortions, interpolation occurs, which means that if there are many small details in the frame, the quality will be inevitable. If most of the image is occupied by the sky, the interpolation will not be noticeable.

Teleconverter

Constructively teleconverter can not be attributed to the lenses. But with it you can increase the focal length, which means that it will approach the subject. The small size and low weight are the main advantages of the teleconverter. The advantages include a relatively low cost. Converters produce with different magnification of the focal length. But for winning in the focal length you have to pay the loss of luminosity. If the converter has a multiplicity of 1.5, then the luminosity falls by one degree, if the multiplicity is 2 - by 2 steps. If you rarely use long focal length, it makes sense to purchase a teleconverter. But if you are shooting a sport, concerts or other subjects that require a large approximation, then you should get a good telephoto lens.

In practice, it is important to the concept of the angle of view of the lens associated with the focal length. I will introduce a new concept with the help of two examples.

The longer the focal length, the farther from me the object I can capture. For example, taking a lens with a focal length equal to 18 mm, I can capture a bird sitting on a tree branch a few meters away from me. However, it will turn out in the photo small. If I use a lens with a focal length of 180 mm, then the size of the bird in the photo will be 10 times larger. At the same time I will take pictures in the same place. Thus, lenses with long focal lengths allow you to shoot an object that is distant from the photographer for a long distance. This is relevant in the reporting shooting of sports events, such as football matches, in wildlife photography, where I will not have the opportunity to come close to a cautious animal. Now give another example.

I photograph in a small room a group of 10 people. When shooting with a lens with a focal length of 180 mm, I will have to move away from the group so far that all people “fall” into the frame. But indoors it is not always feasible - the walls are limited. In this case, I need to use a lens with a shorter focal length equal to, for example, 18 mm. Being located close to the portrayed, I can photograph the entire group as a whole. This is true when shooting in a confined space, interior photography.

Thus, the focal length of the lens affects the shooting distance. Namely, the closer I want to go to the object being shot, the lens with a smaller focal length I need. Why is that? Because, the smaller the focal length of the lens, the greater the angle of view.

The lens field of view is the portion of the scene being imaged by the lens.. The field of view can be given the following definition. The double (multiplied by 2) angle between the optical axis of the lens and the line connecting the most extreme displayed point of the scene to be shot with the optical center of the lens is called the angle of view of the lens.

Also, I will introduce the concept of field angle through the construction. Imagine a rectangular image frame. Draw a diagonal between opposite vertices of the frame. The angle between two lines, one of which passes through one vertex and the optical center of the lens, the other through the other vertex and optical center of the lens, can be designated as the angle of view.

Angle of view is measured in degrees.

Comment. For the angle of view of the lens, there is a strict definition, but it requires a more developed conceptual base. You can “plunge” into it in a book from the list of references cited at the end of the article, and get acquainted with a strict definition on page 50. It may be easy for you to understand and understand the definition from the book given on page 196 (“Angle view ").

Figure 4 shows the dependence of the field of view angle on the focal length. 7. The point of shooting, view, shooting parameters remain unchanged for all 9 shots, only the focal length of the lens changes. In the picture, taken with a focal length of 24 mm, on the left is a gray door. With a focal length of 35 mm, it is not in the frame: the angle of the field of view has decreased and the lens no longer “covers” some part of the scene. Review narrowed. In the last 3 pictures taken with focal lengths equal to 105 mm and above, it is difficult to say which environment surrounds the photographer.

Fig. 7. Dependence of the field of view angle on the focal length of the lens.

Note that with increasing focal length, not only does the angle of the field of view decrease, but the size of the imaged object also increases (the image of the object is scaled). The size of the white card and the distance to it remained unchanged in all pictures. However, the dimensions of the depicted object relative to the frame size increased with increasing focal length.

The field of view angle is not indicated on the lens. It can be found in the instructions for the lens or its specifications. Knowing the angle of the field of view helps me in preparing for the staged shooting, when I plan a frame in advance. Here is how.

In some studios, because of their small area, I cannot use a lens with a long focal length. And for reasons that I will discuss further in the third part of the “fundamentals”, this is desirable. Having calculated the minimum shooting distance for a full-length portrait, I choose one or more lenses with suitable focal lengths.

Perspective distortion

Lenses create a perspective image. In other words, the three-dimensional space is projected by the lens onto a flat photosensitive layer according to the laws of a central perspective.

Perspective is a way of representing three-dimensional space, three-dimensional bodies on a plane.The central perspective implies a projection center. The center of the projection, conventionally, coincides with the optical center of the lens.

The perspective remains unchanged at any focal length, respectively, it does not depend on the angle of the field of view. However, her feeling as an observer depends on the focal length of the lens, the size of the photosensitive layer, the size of the photo and the distance from which the viewer views the photo.

If you want to emphasize the realism of the plot, then you can choose a focal length at which the perspective will be felt natural, undistorted, natural. In addition to the focal length, you need to know at what distance your photo will be viewed, and what format it will be.

And vice versa. You can deliberately distort the viewer's perception of the object being shot, reduce or increase the apparent depth of space. Usually, at small focal lengths, the depth of space “increases”, the background “moves away”, at large focal lengths the depth “decreases”, the space “flattens”, the background “approaches”.

Example. If you look at the portrait (Fig. 8) at a distance of about 35 cm from the monitor, then the perspective will be felt undistorted by you (as if you are in the photographer's place). This is true provided that the resolution of your monitor is 1366 x 768

points and image scale is 100%. If the resolution of your monitor is 1920 x 1080 pixels, then the viewing distance at which the perspective feels natural is 25 cm.

Fig. 8. Facial portrait, photographed on a lens with a focal length of 50 mm.

Similarly, the portrait in Fig. 8 will not appear distorted if you approach the screen at an inconvenient distance - 16 cm.

Fig. 9. Facial portrait, photographed on a lens with a focal length of 24 mm.

The effect of the "big nose", which at large ("comfortable") distances from the screen you can see in Fig. 8, is called distortion. This is a geometric distortion. It is characteristic of lenses with small focal lengths. The effect arises because the center of perspective is close to the person’s face. The tip of the nose of the model is located closer than its eyelids and eyebrows to the center of the perspective, so the latter seem smaller in size than the nose.

Summarize the above. Like the field of view of the lens, thanks to which you can build a frame (place or exclude objects from the frame), there is another means of expression in your hands. By changing the focal length and shooting distance, you can control the viewer's sense of perspective, “zoom in” or “move away” the background in the scene being shot.

Some lenses distort the central perspective due to a specific optical design. An example of the distortion is shown in Fig. 10. The picture was taken using a lens, which for a special image called "fisheye" (eng. Fisheye). Angle of view of such a lens

close to the angle of view of a fish's eye - 180 degrees. The focal length of the lens with which the photo in fig. 10 is equal to 10.5 mm.

Fig. 10. Distortion of perspective fisheye lens (from the English. "Fisheye").

Also, the distortion of the shapes of the depicted objects occurs when the optical axis is directed to the object at an angle different from the direct one. For example, the frontal part of a building is usually impressed distorted (the “rectangle” of the facade turns into a trapeze, tapering to the top),

because, usually, the point of shooting is at the level of the first floor of the building. To put the whole building in the frame, I lift the lens up. The optical axis ceases to be perpendicular to the facade of the building.

Such a distortion causes difficulties in architectural photography. It can be corrected by raising the point of shooting, for example, I can take a position in the building opposite. Or you can tilt the plane of sharpness, which in a normal lens is perpendicular to its optical axis. The tilt of the focusing plane can be done, for example, with the help of a special lens, called a tilt lens (from the English. Tilt - “tilt”).

You can learn more about the perspective effects of the lens, for example, from the book on pages 275-277.

Before you enter the next parameter of the lens - luminosity - I will do an intermediate summary.

Focal length - the main parameter of the lens. Despite the fact that it has a specific value and a unit of measurement - a millimeter - it will not be easy to evaluate it with the help of a ruler, because the optical center of the lens is often located outside of the tube. This need not be done. In practice, the parameters associated with the focal length are important: field angles and perspective distortion.

The first parameter is more technical.. Will my field of view be enough to “cover” the entire room in a frame, or is the model in full growth? The second parameter is more artistic. What will the viewer feel if I show the incredibly long legs of a model sitting in a chair? How obvious will the effect be? Or. How can I show a model surrounded by a shady forest and a river winding around a rocky landscape in the background? (“Zoom” in the background).

Discussing both the technical and artistic aspects of photography, we traditionally devote almost more attention to optics than to all the other components of the photo-process. And this is not surprising, because the quality of the lens used largely determines the technical quality of the resulting image, and the ability of the photographer to express his creative ideas and feelings in the form of a photo directly depends on the parameters of the lens. With the massive transition of photographers and amateur photographers from film to digital cameras, the relevance of issues related to the choice and proper use of lenses has not only not diminished, but on the contrary increased. After all, all the flaws of optics, even a little noticeable in the photo, are more than clearly visible on the screen of a quality monitor. In addition, the wide distribution of digital cameras with matrices of a wide variety of sizes resulted in the emergence of new questions and associated with them are not always clear, ambiguously interpreted and often incorrectly used terms and concepts, such as "equivalent focal length", "Crop factor", " equivalent increase "and so on.

   Therefore, we decided to return to the topic of optics again, devoting this article to the main parameters and characteristics of lenses, the features of using lenses on modern digital cameras and the features of choosing appropriate optics for digital SLR cameras.

BASIC PARAMETERS OF OBJECTIVES

The most demanded and actively used in photographic practice lens parameters are its focal length, angle of view and relative aperture. We examined the physical meaning of these optical characteristics using illustrative examples, with diagrams and formulas in the article “Objectively about lenses” of the winter issue (No. 34 (19) / 2004) of the “Consumer. Photographic equipment and video cameras ”, therefore in this article we will not repeat once again. But on the details of the use of these terms we will dwell once more, in more detail.

FOCUS DISTANCE LENS   - one of its most important characteristics. By the magnitude of the focal length (of course, taking into account the size of the matrix of a digital or frame film apparatus), one can judge the “size” of the image of the subject in the resulting photograph. The longer the focal length of the lens, the larger and closer will be the image of the subject in the photograph. Conversely, as the focal length decreases, the angle captured by the lens increases, and a wider panorama can be accommodated in the frame. In accordance with the focal length of the lens (more precisely, from the angle of the lens) in photographic practice it is customary to distinguish the following categories of optics.

Normal (standard) lens   - This is a lens that has an average (of the order of 40-50 degrees diagonal frame) when used on a camera with an appropriate frame or matrix size. In photographic systems designed to use the usual 35 mm perforated film “type 135” (frame size 24x36 mm), a lens with a focal length of approximately 40 to 55 mm will be considered normal. The most common standard lenses for such systems are lenses with a focal length of 50-52 mm. Such a lens in most cases reproduces the perspective in the picture most naturally and habitually for our vision. In other words, a normal lens transmits a relatively wide panorama, while the large-scale correlation of the objects of the survey remains as our eye sees them. When shooting with a lens with a normal (for frame size) focal length, it is easy enough to achieve the impression of naturalness and habitual perception of perspective. This approach allows the audience to focus as much as possible on the natural, optimal balance of the subject and the surrounding space, while not distracting attention with either a distorted perspective or unnecessary separation of the foreground from the rear.

Lenses with a smaller than normal focal length and angle of view diagonally 60 degrees or more are called wide angle . For example, in systems of film cameras with a frame of 24x36 mm in size “wide-angles” are called lenses with a focal length of 35 mm or less. A wide-angle lens fully justifies its name, since a wider than normal angle of view of such a lens allows to fit a much larger space into the frame, to capture a much wider and impressive panorama. In this case, of course, there is a significant change in the nature of the transfer of perspective in comparison with standard optics. Objects in the background become smaller in size compared to the foreground. In addition, the depth of field is subjectively increased (firstly, due to the fact that objects in the background are depicted visually clearer, and secondly, due to the design features of most wide-angle lenses). Wide-angle optics are indispensable when shooting in a limited space (for example, in interior shooting). She is also more than demanded in everyday amateur photography. The most common amateur scenes like "we are all together at the holiday table" and "I and the mountains" simply cannot work without a wide-angle.

Long focal (or telephoto) called lenses with a larger than standard focal length (more than 80 mm for cameras with a frame size of 24mm x 36mm). Such lenses have a smaller angle of view (no more than 30 degrees diagonal frame) and allow you to “zoom in” the subject, giving a much larger, magnified image at the same shooting distance. Therefore, one of the important applications of long-focus optics is portrait shooting. After all, to avoid distortion of the proportions of a person’s face is possible only if the shooting distance is about one and a half to two meters. And at this distance a standard and, especially, a wide-angle lens will give a fairly small image. And only the use of long-focus optics makes it possible to simultaneously obtain the correct, natural proportions of the face and figures of a person, and to achieve the most expressive and balanced composition of the frame. Details in the background when shooting with a long-focus lens are depicted on a larger scale, and therefore the drop in clarity and detail of the background image becomes much more noticeable. A long-focus lens is an excellent tool when it’s impossible (or difficult) to get closer to a subject to take a picture of it on a fairly large scale, or when it becomes necessary to focus on some small details and close-ups of the subject, cutting off and erosion beyond recognition an unnecessary background. In addition, telephoto lenses convey a perspective in a very special way, “flattening” it and reducing the distance between the foreground and background. Closest to our perception, the road blocked by cars, the path lost in the haze, the rails stretching into the distance, or the even row of house facades are best and easiest to convey with the help of long-focus optics. The longer the focal length of the long-focus lens differs from the standard one, the more noticeable will be the enlargement of the main subject in a future photo, and the more compressed the perspective in the image will be perceived.

The second important characteristic of the lens (more precisely, a couple of characteristics), on the detailed description of which we would like to stop, is the angle of the lens image field and the angle of view of the lens on the film (or matrix) of the camera.

ANGLE OF VIEW LENS   - this value is determined by the ratio of the focal length of the lens and the size of the matrix (or film frame) of the camera.

The smaller the focal length of the lens, and the larger the frame size of the film or matrix, the wider the panorama can fit within the frame. Conversely, with increasing the focal length of the lens and reducing the size of the matrix (film frame), the image in the photo will be a narrower, bounded frame "look" at the surrounding reality. The angle of view of a pair of lens-matrix (or lens-frame film) depends solely on the size of the matrix (frame) of the camera and the focal length of the lens. (This rule does not work only in one single case - for a super wide-angle lens of a special fish-eye design, designed to produce a special “inverted” image.) The angle of view of each lens, given in most tables and reference books, is usually indicated based on the size diagonal frame film (or matrix), to work with which the lens is designed. For example, the angle of view of lenses for 35 mm system film mirror devices is calculated based on the diagonal size of the standard (24x36 mm) film frame and is about 43 mm. However, if the same lens is installed on the corresponding digital system DSLR with a matrix of reduced size, then the angle of view of the same lens will already be noticeably smaller. In other words, the same lens when working with a smaller frame will become like a “long focus”.

It would be logical to continue our reasoning in the "opposite" direction. That is, suppose that increasing the size of the matrix (film frame), the angle of view of the lens will increase accordingly. However, this can only be assumed in the case of the “ideal” lens. In real life, of course, there are no perfect lenses. And for each real lens, one of the important optical characteristics is the angle of the image field (and the associated field size of the lens image). These parameters describe the maximum image size that a lens can build on a film or matrix. If the size of the matrix (or film frame) at least slightly exceeds the size of the lens image field, then a noticeable drop in sharpness will be observed in the corners of the photo. A significant discrepancy between the size of the image field and the frame size can even lead to the so-called "vignetting", that is, darkening the edges of the frame. Therefore, in order to prevent such problems, it is necessary to observe an important rule - use only lenses whose image field size is larger than the diagonal of the frame.

For a clear illustration of this effect, we give an example of three lenses with the same focal length, but constructed according to different optical schemes and designed for use on cameras with different frame sizes — Flektogon 50 mm f / 4 (wide-angle lens for medium format cameras with a frame size of 6x6cm), Canon EF 50mm f / 1.8 (standard lens for 35mm cameras with a frame size of 24x36 mm) and Zuiko Digital ED 50mm f / 2.0 Macro (long focal macro lens for Four Thirds digital cameras with a frame size of 13.5x18 mm). Despite the same focal length of all three lenses, only the Flektogon 50mm f / 4 lens, designed as a wide-angle (image angle of about 80 degrees), can create an image about 9 centimeters in diameter, sufficient to cover a 6x6 cm frame. - standard Canon EF 50 mm f / 1.8 (angle of view about 50 degrees) and long-focus Zuiko Digital ED 50 mm f / 2.0 Macro (angle of view about 30 degrees) is not able to perform the functions of a 50-mm wide angle in the system of medium format cameras, because their image The diameter has a diameter of only slightly more than 50 mm / 25 mm, respectively (instead of the 90 mm required for this). On the other hand, the functions of a standard 50 mm lens in a system of 35 mm film cameras with a frame size of 24x35 mm can be performed not only by specially designed for this purpose Canon EF 50 mm f / 1.8, but also by the wide-film wide angle Flektogon 50 mm f / 4. And the functions of a long-focus lens in the “four thirds” digital SLR camera system can be performed by any 50 mm lens from the three presented by us - any of them cover the 13.5x18 mm matrix without vignetting and any other problems.

Naturally, the use of a huge, heavy and less high-aperture medium-size lens instead of the same in function, but noticeably lighter, compact and high-aperture lens, specially designed to work in the “four thirds” system, is more a theoretical idea than a practical necessity (the moreover, the adapters used in this case significantly degrade the functionality of the camera). In addition, the difference in the method of attaching the lens to the apparatus makes such experiments more difficult. And putting a lens from a digital 4/3 DSLR on a 35mm or a medium format DSLR is an impossible task, because in this case the mirror will prevent the lens from sharpening this lens to infinity.

So why did we dwell on this problem in such detail, which was previously known only to photographers working with large-format cardan and field cameras?

The reason for this is the wide distribution of relatively inexpensive system digital SLR cameras Canon, Nikon, Pentax, Sigma and Minolta, compatible in optics with 35 mm film mirror devices of the same companies. The reduced (compared to the 24x36 mm frame) matrix dimensions of these digital devices led over time to the need to develop wide-angle and standard zoom lenses optimized for use with the APS-C matrix, since any lens from a film SLR when used on a digital SLR has noticeably smaller angle of view. For telephoto lenses, of course, this is convenient. But wide-angle optics immediately lose their remarkable properties. Therefore, when the number of manufactured digital cameras with a “half-frame” matrix (15.6x23.7 mm or 15x22.5 mm) became significant, and their prices became quite democratic, special lenses designed to work with such a matrix appeared on the market. The first "half-frame" optics released by Nikon (DX lens series - AF-S DX 12-24 / 4 IF ED, AF-S DX 18-70 / 3.5-4.5G IF ED, AF-S DX 17-55 / 2.8 G IF ED and AF DX Fisheye 10.5 / 2.8D ED) and Canon (EF-S lens series - EF-S 18-55 / 3.5-5.6, EF-S 10-22 / 3.5-4.5 USM and EF- S 17-85 / 4-5.6 IS USM). And now most manufacturers of optics already have whole lines of special “half-frame” lenses - for example, the Pentax “DA” lens series (DA 14 / 2.8, DA 16-45 / 4 ED AL, DA 18-55 / 3.5-5.6 , DA 50-200 / 4-5.6 ED) and the DC series of the Sigma (10-20 / 4.0-5.6 EX DC HSM, 18-50 / 2.8 EX DC, 18-50 / 3.5-5.6 DC, 18-125 /3.5-5.6 DC, 18-200 / 3.5-6.3 DC, 55-200 / 4-5.6 DC, 30 / F1.4 EX DC HSM). Special “digital” lenses are most often, figuratively speaking, “reduced analogs” of standard and wide-angle “full-frame” zoom due to the fact that they are designed to cover a “half-frame” matrix (and not a full frame of 24x36 mm), and the focal length range is proportional to shifted downwards. For example, the Canon EF-S 17-85 / 4-5.6 IS USM lens when used on Canon EOS 300D, EOS 350D and EOS 20D digital SLRs is almost completely identical to the Canon EF 28-135 / 3.5-5.6 IS USM full lens. functionally (when using the latter on film mirrors), and in size and even in appearance!

However, with the release of relatively inexpensive “half-frame” digital SLR devices, the film technique did not go to scrap. Quite a few photographers use both digital and film devices at the same time. Moreover, for some of them, the main criterion for choosing a digital device was compatibility with optics and accessories with the film system on hand. And if you can use almost any lens from a film device on a digital SLR, then you can install a “digital” lens on a film SLR in most cases (since the bayonet of digital lenses Nikon, Pentax, Minolta and Sigma is fully compatible with the bayonet of the corresponding film devices ). But when trying to photograph, it turns out that a special “digital” lens is able to cover with an image of only about two-thirds of the film frame area. Alas, such a lens cannot work with a “free wide-angle”, and the place is for it exclusively on digital devices with a “half-frame” matrix. However, Canon alone decided to install a kind of fuse prohibiting the use of “half-frame” optics on full-frame digital and film devices, having developed a special EF-S bayonet for their “half-frame” digital lenses, mechanically incompatible with the standard EF bayonet. At the same time, the response bayonet EF-S of “half-frame” digital DSLRs EOS 300D, EOS 20D and EOS 350D is designed in such a way that it allows you to install and use any lens with no restrictions with either the new EF-S bayonet or the standard EF bayonet.

Let us pay attention to the second reason, for which the use of specially designed lenses is desirable as a normal and wide-angle optics on a digital camera. Light-receiving sensors of digital cameras (CMOS and CCD arrays), unlike film, are much more critical for the angle of incidence of light rays. And if the rays hit the surface of the matrix not perpendicular to its surface, but at a sharper angle, then some of the light no longer falls on the photosensitive surface of the photodetector due to partitions between the cells. This feature of the matrix operation leads to the fact that when used on digital SLRs of some lenses that were designed to work on film devices, the image at the edges of the frame noticeably loses clarity, becomes somewhat darker, and in some cases color artifacts may even appear. To prevent this unpleasant phenomenon, lenses for digital devices must have the properties of so-called "telecentric" optics. The main advantage of telecentric optics is that it ensures that the rays of light hit the camera matrix almost perpendicular to the surface not only in the center of the frame, but also at its edges. Due to the optimum angle of incidence of light rays on the matrix, a properly calculated lens allows for better clarity, uniform brightness and correct color rendition throughout the image field.

The term “telecentric optics” was first introduced by Olympus Optical into a wide circle, introducing the “four thirds” digital camera system developed by it. In this case, of course, the company promised that the newly calculated Zuiko Digital optics for the new system will have telecentric properties, which means the pictures will be bright and sharp from edge to edge.

Modern lenses from other companies, designed for use on both film and digital technology, are also being developed taking into account the specifics of using them on digital SLRs, or (at least) undergo mandatory testing for the absence of obvious problems when working in a “digital” version. As an example of such universal optics, we can take Canon EF 24-70 / 2.8 L and Canon EF 17-40 / 4 L lenses. Another example is Sigma, which has “taken inventory” of a considerable number of its lenses for compatibility with digital devices. As a result of this work, more than half a dozen lenses have been replaced by analogs that have the abbreviation “DG” (Digital Grade) in their name, that is, recommended for use on digital devices as well.

We see that there are more and more lenses, both designed for use with “half-frame” digital SLRs and equally suitable for use on digital and film SLR cameras. Therefore, we hope that due to the wide distribution of lenses specially designed for the use of digital devices, problems with image quality (even with the growth of “megapixels” of this class of photoequipment in the future) will not be observed.

NEW TERMS

In appearance, digital mirror devices differ very little from film ones; they use practically the same flashes and lenses. And according to the control concept, film and digital cameras differ little from each other. However, the combination of external and functional similarity of digital and film mirror devices with the difference in film and matrix frame sizes (due to technical and economic reasons) led to a number of questions concerning the use and classification of interchangeable optics.

Before the era of amateur digital DSLRs with a classification of lenses was all much easier. The bulk of amateur, semi-professional and professional SLR cameras with interchangeable optics, as well as the main part of the “soap cases”, combined the format of the 35 mm perforated “type 135” film used in them and the frame size of the film 24x36 mm.

Less common photographic materials of other sizes were used either in openly amateur systems (“type 110”, “type 126”, “disc”, APS), or in serious professional work (60 mm roller film “type 120” and “type 220”, flat format film). Photographic equipment using the “type 135” film dominated the photographic equipment market for many decades, not giving up its position even now. Therefore, photographers and amateur photographers for several generations have become accustomed to the fact that the properties of the interchangeable lens is quite correct and most convenient to describe it with a focal length. For example, a lens with a focal length of 50 mm was clearly perceived as a normal (standard) lens. The focal length of 35 mm or 28 mm uniquely characterized the lens as wide-angle. And only a portrait long focus lens could be 85 mm or 135 mm. That is, of course, everyone understood that "normal" is a lens from an angle of about 40-50 degrees. But since the frame size of most devices is the same (24x36 mm), then the angle of view of the lens depends only on the focal length. Especially since the focal length is always written on the rim of any lens, and the angle of view can only be learned from the lens or ID of the passport. Apparently, it is for this reason that the steady habit of characterizing by the magnitude of the focal length the lens designation as normal, wide-angle or long-focus, has taken root among photographers and amateur photographers.

Equivalent focal length

With the advent of the digital apparatus era on this habit that has been cultivated for decades, there was almost a fat cross. The variety of matrix sizes of digital devices is simply amazing - from “full-frame” (24x36 mm), “half-frame” (APS-C format, approximately 16x24 mm) and “quarter-frame” (“type 4/3”, size 13.5x18 mm) to in compact and miniature digital devices "type 2/3", "type 1 / 1.8" and "type 1 / 2.5" (the largest of which do not exceed the size of the nail of the little finger of the hand). And such a characteristic of a digital camera zoom lens, as the "focal length range

7.2-50.8 mm ”practically doesn’t say anything to the modern amateur photographer, even with the knowledge of the real size of the matrix 2/3” - 6.6x8.8 mm. Therefore, in order to achieve some clarity and convenience in this case, it is necessary to find the corresponding formulas in the photo reference book, calculate the appropriate lens angle taking into account the matrix size, and then compare these data with the parameters of the usual lenses calculated for a 24x36 mm frame. As a result, it turns out that a lens with a focal length of 7.2 mm on a 2/3 ”matrix has about the same diagonal as the wide-angle lens with a focal length of 28 mm on a frame of 24x36 mm. And at the 50.8 mm position, the same lens sees the world just as a 200mm long-focus lens mounted on a 35mm camera. That is, the above-mentioned lens with a focal length range of 7.2-50.8 mm, mounted on a digital device, can be used in the same way as a zoom with a focal length range of 28-200 mm on a conventional 35-mm SLR. This is already valuable and understandable information, which is convenient and pleasant to use! Therefore, the step of the manufacturers, who indicated in the camera’s characteristics not only real numbers of the lens’s focal length, but also calculated in the same way as we did above, the numbers, which were called the “equivalent focal length”, became quite logical. Based on the values ​​of the equivalent focal length, we can easily imagine the parameters and capabilities of the lens mounted on the camera.

Some manufacturers even went further. For example, on the Konica Minolta DiMAGE A200 on the lens zoom control ring, the numbers are not the real, but the equivalent focal length. And this decision is the right one - after all, for conscious control of the perspective, it is important to know first of all the angle of view of the lens (which we are most accustomed to perceive in the form of numbers of equivalent focal length). But the numbers of real focal length, indicated on the front panel of the lens mount, the user of such a camera, most likely, will never need.

Crop Factor

Users of system digital SLR cameras found themselves in a somewhat more complicated situation. On the one hand, it is clear that due to the smaller size of the matrix in comparison with the 24x36 mm film frame, all lenses become as if “long focus”. For example, the Canon EF 50 / 1.8 used on a film camera as a standard lens when mounted on a Canon EOS 350D digital camera immediately acquires an angle of vision, typical of a portrait lens. On the other hand, there is no point in remarking all lenses, since they can be used not only on a digital SLR with a “half-frame” matrix, but also on devices with other frame sizes - film, full-frame (for example, Canon EOS 1Ds mkII) and almost full-frame ( for example, Canon EOS 1D mkII) digital devices. Therefore, for users of digital SLR cameras with a smaller film frame than a matrix, a more convenient method for calculating the equivalent focal length was the use of a lens angle of view reduction factor (other names for this factor are “crop factor” or “magnification factor of equivalent focal length” ). Crop factor numerically represents the ratio between the size of the diagonal of a frame 24x36 mm and the size of the diagonal of the matrix. In this case, the approximate equivalent focal length of the lens can be obtained by multiplying the real focal length of the lens by the conversion factor (crop factor).

For each matrix size, the lens angle reduction factor has its specific values. For example, for Nikon, Dynax and Pentax digital mirror devices the magnification ratio of the equivalent focal length is 1.5, for Canon EOS 1D and EOS 1D mkII - 1.3, for Canon EOS 10D, 20D, 300D, 350D, D60 and D30 - 1.6, for Sigma SD-9 and SD-10 - 1.7, and for the devices of the 4/3 system - 2.

Finishing the topic of recalculation of the real focal length to the equivalent, let us dwell on a very important point. The figure of the equivalent focal length (that is, the product of the real focal length by the crop factor) is intended only to be used in terms of 35 mm film photographic to describe the angle of view of the lens. The actual focal length of a lens mounted on a digital camera does not change. Accordingly, all other calculations (for example, the calculation of the depth of field and the determination of the optimal degree of aperture) should be carried out on the basis of the actual, rather than the equivalent value of the focal length. For example, on a Nikon D70 digital “half-frame” device (crop factor 1.5), you can use a 35 mm f / 2 D wide-angle AF Nikkor lens as a standard one, since the equivalent focal length will be around 50 mm. However, visually, the depth of field at the same aperture values ​​will be noticeably larger than when using a lens with a focal length of 50 mm on a film SLR (although the angle of view will be the same in both cases). In this case, it is possible to achieve the same depth of field for the separation of the foreground and background by opening the aperture at least one - two steps additionally.

The same roots have noticeable “flatness” and “uniformity” of the image, inherent in compact digital cameras with a matrix of 2/3 ’’ or less. After all, the real focal length of the lenses of such devices is at least 4-5 times (!) Less than the equivalent. Therefore, even with a diaphragm of 2.8, the depth of field of a compact digital device’s lens turns out to be quite comparable with the depth of field of a corresponding lens of a 35-mm film SLR when shooting a similar plot on a diaphragm of at least 8-11.

Equivalent increase

“Zoom” is another conventional and conventional value to which photographers and amateur photographers have been accustomed to prolonged use of 35 mm film photographic equipment with a frame size of 24x36 mm. Based on the magnification of the maximum magnification (or the maximum image scale, which is the same), we judge the applicability of such a lens for shooting on a large scale or even for using it in macro photography. For photographers and amateur photographers accustomed to the use of 35-mm film photographic equipment, it is not difficult to classify the macro-properties of the lens according to the maximum image scale. For example, a lens that can focus up to a 1: 1 scale (“one to one”) is a full-fledged modern macro lens. The maximum scale of 1: 2 ("one to two") can boast of either relatively inexpensive macro lenses or macro lenses of the old design. And if the maximum image scale of a lens is 1: 5 or even less, then such a lens is considered practically unsuitable for shooting small objects close up.

(By definition, the scale is the ratio of the linear dimensions of the image on the film (matrix) to the size of the subject. If the subject is twice as large as its image on the film, then this ratio is otherwise called “1: 2 scale.” the same dimensions as the subject, in this case the scale is 1: 1. Consequently, the larger the maximum scale, the smaller object can be photographed “for the whole frame.”)

We now turn to digital devices with a matrix of reduced size. In this case, in order to photograph an object of the same size in the whole frame, a smaller increase is quite sufficient (after all, the matrix size is smaller!). For example, a lens that provides a 1: 1 shooting scale is necessary for photographing a full-size brand with a size of 24x36 mm film-making apparatus. If we use a digital device with a “half-frame” matrix (15.6 x 23.7 mm, the diagonal size is 1.5 times smaller than that of a 24x36 mm frame) for such a shooting, then it turns out that already with a smaller magnification ratio (1: 1.5, “one to one and a half”) image of the brand occupies the entire area of ​​the frame. An even smaller increase for such a survey would be required for devices with an even smaller matrix size - approximately 1: 2 for a 4/3 system “quad-frame” device (the matrix diagonal size is 2 times smaller), 1: 4 for devices with 2/3 'matrix '(the size of the diagonal of the matrix is ​​4 times smaller) and so on. However, despite the different zoom ratio when shooting, the result can be considered the same - the image of the brand takes up almost the entire field of the frame. Therefore, it would be logical to simplify the transfer of “film” concepts to digital equipment to introduce one more “equivalent” parameter - “equivalent increase”. The meaning of the equivalent magnification, in general, is about the same as in the case with an equivalent focal length - the sameness of the effect when shooting with a film and digital camera. And the coefficient of conversion of real magnification into equivalent is numerically equal to the ratio of real and equivalent focal length.

We give a real example. The macro lens for the 4/3 camera system (crop factor 2) Zuiko Digital ED 50 mm / f2 has a real focal length of 50 mm and can be focused up to a maximum magnification of 0.52x (i.e. approximately 1: 2). At the same time, the equivalent focal length of such a lens will be 100 mm, and the equivalent magnification - 1.04x (that is, approximately 1: 1). Accordingly, this lens on 4/3 system cameras will be functionally similar to a 100 mm macro lens with a maximum 1: 1 image scale in a 35 mm film camera system with a frame size of 24x36 mm. On the other hand, the Nikkor AF Micro 105 mm f / 2.8D lens, which has a maximum zoom ratio of 1: 1 when working with Nikon film cameras, when installed on a Nikon digital reflex camera (Crop Factor 1.5) will not only have an increased one and a half times the equivalent focal length, but will also be able to produce more coarse shots (to an equivalent scale of 1.5: 1).

Aperture and relative aperture

Aperture is another extremely important lens specification. As the name suggests, the aperture characterizes the brightness of an image that a lens is capable of building on a film (or matrix). The brighter the lens, the brighter the image it can create. Conversely, a less fast lens creates a darker image. The aperture speed of a lens is characterized by the value of its relative aperture (that is, the ratio of the diameter of the effective aperture of the lens to its focal length) and is denoted as a fraction. For example, for a lens with a relative aperture of 1: 4 (often the f / 4 marking is common), the diameter of the effective aperture is four times smaller than the focal length value. In this case, we note that the size of the actual lens opening is a virtual value. It usually does not exactly match either the diameter of the front lens or the size of the diaphragm. Therefore, the size of the effective lens opening cannot be measured, it can only be calculated.

Typical values ​​of the relative aperture of the lens are usually directly dependent on the size of the image field, for covering which such a lens is designed. The smaller the size of the matrix (film frame), which the lens is designed to service, the more high-aperture it can be made at comparable (and even less!) Costs and complexity of the design. For example, the zoom lenses of modern compact digital video cameras, designed to work with a 1/6 ″ matrix, can have a relative aperture of up to 1: 1.2 (JVC GR-DV3000), and values ​​of 1: 1.6-1: 1.8 became standard in this class. For interchangeable lenses, the 35 mm DSLRs of the “aperture” aperture ratio are noticeably lower - the relative aperture 1: 2.8 has only some professional zoom, and for other zoom lenses the maximum aperture ratio is 1: 3.5–1: 4.5 and even . In this case, we note that lenses with a fixed focal length, as a rule, have a significantly higher aperture ratio than optics with a variable focal length. For example, for the same 35 mm DSLRs, there are quite a lot of lenses with a fixed focal length and relative aperture of f / 1.4-f / 1.8, while lenses with aperture of less than f / 2.8 practically do not occur (except among super-telephoto lenses). In addition, optics with a variable focal length often to simplify the design has not a constant, but a variable value of luminosity, depending on the focal length. For example, a zoom lens 18-70 / 3.5-4.5 with a focal length of 18 mm has a relative aperture of f / 3.5, with a focal length of 25-50 mm - f / 4, and at a maximum focal length (70 mm) the value of the relative aperture falls to f / 4.5. Taking into account the highly developed automation of modern cameras equipped with light metering through the lens, the variable aperture of optics practically does not cause any inconvenience.

Diaphragm and depth of field

At the maximum relative aperture, photographic lenses are used quite rarely. A large luminosity of the lens usually acts as a margin that the pocket doesn’t pull and can be used if necessary (a small amount of light, the need for a minimum depth of field, etc.). The bulk of the shooting requires a much smaller relative aperture of the lens. Therefore, each photographic lens is equipped with a device for operative regulation of the relative aperture - a diaphragm. The process of reducing the lens aperture with the help of the diaphragm is called “diaphragmization”, and the reciprocal of the relative aperture value of the lens is called the “diaphragm number” (or simply “diaphragm”). In the process of diaphragm, the effective aperture of the lens is reduced, and the brightness of the image created by the lens is directly proportional to the area of ​​the active aperture of the lens. By reducing the diameter of the effective lens opening by 2 times, it is possible to reduce by 4 times the amount of light passing through it. Accordingly, the brightness of the image becomes smaller as the f-number increases. The values ​​on the lens aperture scale are now made to choose from the standard range - 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, and so on. Such a step of the aperture values ​​is chosen primarily for convenience, because the transition to the next in the row aperture value, the amount of light passing through the lens doubles. Therefore, the lens aperture of 1 degree (for example, from 2.8 to 4) results in the same decrease in exposure as a shortening of the exposure by 2 times.

Of course, you should not identify the aperture only with the function of reducing the brightness of the image on the film (matrix). With diaphragmization, there are still a number of changes in the nature of the image created by the lens - the depth of field increases, the sharpness properties of the lens and its design change. So now, in the era of highly sensitive arrays and high-speed shutters, lens iris is used more often not as a means of controlling the amount of light, but as an artistic technique that allows you to place accents in the ratio of foreground and background by choosing the optimal depth of field.

The concept of depth of field and the formula for calculating the depth of field were discussed in detail in the article “Objectively about lenses” of the winter edition of the “Consumer. Photographic equipment and video cameras ”(№ 34 (19) / 2004). Therefore, we only repeat the conclusions of this article. So, the depth of the sharply depicted space (this is the most correct way to call this characteristic) is generally greater, the smaller the lens aperture, the smaller the focal length of the lens (a subjective increase in the depth of field), and the greater the distance to the subject. Also, the depth of the sharply depicted space strongly depends on the subject and on the sharpness parameters of the optics and film (matrix). The loss or apparent deterioration of the image detail quite clearly distinguishes between sharpness and unsharpness. Therefore, the use of sharp optics, high-quality large-format matrix (or fine-grained film) with high resolution and the presence of numerous small details on the subject make even a slight defocusing of the image well visible. And vice versa - if not very high-quality optics are used, if the camera matrix is ​​not very clear, if the subject is devoid of clear contours and fine details, the apparent depth of field becomes larger.

Considering the characteristics of modern compact digital cameras, it is easy to notice the following patterns. The focal length of camera lenses built on miniature (2/3 ’’ and less) matrices is quite small (4-6 times shorter than the optics of the same angle of view for 35-mm SLRs). And the matrices themselves, due to the peculiarities of their structure, do not cope well with the image of particularly fine image details (hair, wool, fine textures, and so on), the transmission of which most easily traces the boundary between the sharpness and blurring zones. In addition, the quality of transmission of small parts and textures further deteriorates as a result of image processing by the camera processor. After all, the miniature matrix of compact digital cameras "noisy" strongly even at low sensitivity. Therefore, noise suppression systems on such devices work, as a rule, rather aggressively, saving the image not only from noise, but also from small details. And the process of automatic enhancement of image clarity (the obligatory stage of processing) makes the transition between zones of sharpness and blurring even less noticeable, which is subjectively perceived as an additional increase in the depth of the sharply depicted space. Therefore, the depth of the sharply depicted space when using such cameras is quite large even at maximum values ​​of aperture of the lens. Well, on the “habitual” in film phototechnique values ​​of the aperture 5.6-8, the depth of the sharply depicted space that has increased beyond measure simply does not allow using this artistic technique, separating the foreground from the rear. It is also worth noting that the small focal length of the optics of such cameras also leads to the fact that the physical diameter of the diaphragm at a f-number of 8 or more becomes so small that it can lead to a significant drop in sharpness due to diffraction phenomena (see the article “Objectively about lenses ”,“ Consumer. Photographic equipment and video cameras ”No. 28/2002).

Digital cameras with a matrix of a much larger size (4/3 cameras and half-frame SLR cameras) provide much more possibilities in terms of the artistic use of the depth of the sharply depicted space. However, when working with these devices, it is necessary to remember that in order to achieve the necessary effect of separating the foreground and background, it is desirable to open the diaphragm at least 1-2 steps stronger compared to the usual 35 mm photo equipment figures.

On the other hand, scenes that require a large depth of sharply depicted space when shooting are much easier to “work out” with the help of digital devices. For example, in the case of catalog subject shooting, the ability to achieve the required depth of field with noticeably less deep diaphragm can significantly reduce the power requirements of studio lighting and make such shooting faster and more convenient.

ZOOM lenses

It is more correct to call them lenses with variable focal length (OPFR). This phrase exhaustively explains their essence. In such lenses, the focal length changes continuously, due to the smooth movement of the internal lenses along the optical axis. Zoom lenses of most compact cameras have a motor drive and, as a result, work slowly and require power. In advanced camera models, only manual zooming is used. The main advantages of OPFR: a smooth transition from a general plan to a large one without loss of quality (if quality were not important, one could simply increase the required fragment when printing); the ability to crop images; "Management" of perception of perspective. Zoom lenses can, like regular (fixed), belong to different groups - normal (for example, 35-70 mm (in 35 mm equivalent)), long-focus (70-300 mm, 80-200 mm, etc.). p.), wide-angle (17-35 mm, 24-50 mm, etc.). The most widely used in budget photography are universal zoom lenses with a range of 28-90 mm or 35-140 mm. They allow to conduct both landscape, and portrait shooting. Making a high-resolution multi-function zoom lens is expensive money, but the alternative is a bag of “wide-angle”, “staff” and “portrait” photos, which the photographer has to carry along for all occasions. Poorly productive OPFR is much simpler in the device, they are light in weight and low in price. Note that the ratio of the maximum focal length to the minimum is called the multiplicity of the lens. So a zoom lens of 35-140 mm has a multiplicity of 4 and can change the scale of shooting four times.

Lens are one of the basic elements in photography. To select and use the "correct" lens, you need to know their basic parameters: sharpness, viewing angle, depth of field and perspective.

Sharpness

Sharpness   - one of the most important characteristics of each lens! You can compensate for distortion (distortion), vignetting (vignetting), color and other optical distortion of the lens, but it is impossible to correct the sharpness - using the effects of “Smart Sharpen” or “Unsharp Mask” when processing a photo will help to visually improve slightly sharp images, but it will not help when processing images taken with a “bad” lens.

A perfectly clear result can only be expected from a “perfect” lens. In fact, only the best lenses (for example, the Canon “L” series) provide excellent sharpness in all aperture values, while most lenses blur the image to one degree or another when fully opened, this is improved by dimming the lens by one, two steps. For example, Canon 24-105 L IS and Canon 600 f4 L IS lenses are very clear even when fully opened, at f / 4, while the Sigma 180 Macro lens provides excellent sharpness at f / 8, but lubricates a little when opened with f / 3.5.

Sigma 180mm Macro, f / 3.5

Sigma 180mm Macro, f / 8

Darkening the lens with an aperture improves sharpness, since when using a small aperture only the light that passes through the central part of the lens is fixed. When buying a new lens, it is recommended to take several test shots at different aperture values ​​to evaluate its sharpness. If you need a wide aperture, it is advisable to choose the appropriate lens - it makes no sense to buy a standard or telephoto lens unsuitable for shooting with a wide aperture, while you can not worry about the performance of wide-angle and macro lenses, which are often used with a small aperture (f / 8 - f / sixteen).

After reading these lines, you might think that the more the lens are dimmed with a diaphragm, the better the result will be. This will be true until you reach f8 or f11, then the sharpness is significantly reduced. At minimum values, such as f / 32, all lenses lose sharpness to an unacceptable level. The reason for this is diffraction or refraction of light: this phenomenon affects absolutely all lenses, since it has a physical nature; it cannot be avoided; This is not an optical distortion. So what is it? At that moment, when a wave passes through a hole whose width is comparable to a long wave, it changes the angle of propagation. It is precisely because light is a wave, and the aperture is a hole, a lens, and is subject to diffraction. The magnitude of the refraction depends on the diameter of the aperture. With a large aperture, the refraction is insignificant, whereas with a small aperture diffraction becomes a serious problem: it is usually preferable to avoid an aperture smaller than f / 16.

Sigma 180mm Macro, f / 8

Sigma 180mm Macro, f / 32

Viewing angle

The viewing angle is determined by two variables: the focal length and the size of the sensor. Most camera systems are offered with a wide range of focal lengths from 12mm. up to 600mm. There are four formats of professional (SLR) cameras:

• 4/3 (sensor 18x13.5 mm.)
• APS-C (sensor 25x16.7 mm.)
• 35mm (sensor 24x3 mm.)
• digital medium format (sensor 36x48 mm.)

The formula for calculating the viewing angle is quite simple: angle = 2 * arctan (D / 2f)where D is the diagonal of the sensor, f is the focal length. In each format, the focal length gives a viewing angle of about 46 °, which is considered “standard”, as it has approximately the same viewing angle as the human eye. Lenses with less focus are called wide angle, since they give a greater viewing angle; large focus lenses are called telephoto   and give a narrower viewing angle.

The following table and images show the value of the viewing angle at different focal lengths in four different formats.

	7	12	14	16	21	24	2	35	50	70	105	200	300	400	500	600	1200
4/3	116.2	86.30	77.56	70.22	56.35	50.22	43.77	35.63	25.36	18.26	12.23	6.43	4.29	3.22	2.57	2.14	-
APS-C	-	102.8	94.14	86.49	71.25	64.18	56.51	46.53	33.50	24.26	16.31	8.60	5.74	4.30	3.44	2.87	1.43
35mm	-	122.0	114.2	107.1	91.74	84.10	75.42	63.47	46.82	34.37	23.30	12.35	8.25	6.19	4.95	4.13	2.06
Mf	-	-	-	-	-	-	93.94	81.20	61.92	46.39	31.89	17.06	11.42	8.57	6.86	5.72	-

  - one of the fundamental principles of photography. When you focus on an image, only a certain plane (distance) will be really focused. Everything that is before or behind this plane will gradually "blur"; areas near the focal plane that still have acceptable clarity constitute the depth of field.

There are three main factors that affect the depth of field. The first one is an aperture. The aperture width, such as f / 2.8 or f / 4, gives “shallow” depth, while small apertures (such as f / 16 and f / 22) give greater depth.

You must choose an aperture depending on the result you want to get. If it is necessary to separate the subject from the background, then it is necessary to use a wide aperture; In the case when it is necessary that the objects in the front and in the background be in focus (for example, shooting panoramas, landscapes), it is necessary to use a small aperture, for example f / 16.

The second factor is focal length   - Also associated with the depth of field and background. With the same object size, for different lenses, the depth of field will be the same. For example, we photograph a butterfly: with the same aperture, we get an identical depth of field at focal lengths of 50 mm. and 200 mm. The difference in the case of a focal length of 200 mm. in a narrower viewing angle, which gave a significantly cleaner background.

The size of the object is the third factor. If you shoot a large object, you will receive a proportionally greater depth of field. For example, when shooting a mountain at f / 5.6 we get a greater depth of field, while when shooting a butterfly, with the same aperture, the depth of field will be much smaller.

How to get the best result from the depth of field?

When photographing animals, focus on the eyes of the animal and choose an aperture that gives the correct depth of field for a particular image. For small animals, such as birds, it is better to use an aperture of f / 8 or f / 11, and for larger f / 4 or f / 5.6. When macro photography try to shoot the object at a right angle.

  When photographing nature, landscapes technique is slightly different. Some photographers are trying to calculate the depth of field and hyperfocal distance (the distance that gives the greatest depth of field at a given aperture) - a waste of time! It is preferable to use a simpler and more intuitive way to focus: with a wide angle and an aperture of f / 16, you will get the widest possible depth of field — the simplest way to get the entire image in focus. If the closest object in the composition is 2-3 meters, focus on 6-8 meters and use the f / 16 aperture - get a sharp shot from the nearest object to infinity; if the nearest element is a meter or less, focus on 1.5 - 2 meters with an aperture of f / 16 (or f / 22 if the closest element is very close). To check the focus, you can view the image later using the camera's display.

Perspective

In theory, if the camera-object is kept at a constant distance, then the perspective for all lenses should be the same, but in practice wide-angle lenses allow you to organically enter an object that is very close to the camera into the composition, while telephoto lenses allow you to occupy the entire frame space remote object.

As a result, wide-angle lenses tend to distort perspective, while telephoto lenses provide a “squeezed” or “flat” perspective. Perspective is the most important element of creativity, affecting the perception of the picture: when photographing landscapes, a wide viewing angle gives a sense of depth to the image, thanks to a peculiar perspective. On the other hand, if you want to focus on the details, a long focal length allows you to enhance the two-dimensional and detailed photos.

The following photos are a good example of a different wide-angle and telephoto photograph: The first shot was taken with a focal length of 17 mm. - perspective hypertrophied - gives a sense of depth. The second shot is taken with a focal length of 105 mm. the branches in the foreground and the tower appear to be on the same plane, although in reality they are at a sufficient distance.