Knowing what focal length is and what the features are is especially important when buying lenses. This lesson will give you information on how lenses with different focal lengths work, how to use them creatively and choose the ones that are right for you.

Step 1 - What does it really mean?

The focal length of your lens basically determines what zoom will be in your photos: what more number, the greater the zoom effect will be.

Focal length is often misunderstood, saying that it is measured from the front or back of the lens. It is really the distance from the convergence point to the sensor or film in the camera. Look at the diagram below where this is explained

Step 2 - Different focal lengths and how they are used

Ultra Wide Angle 12-24mm

These lenses are considered highly specialized and are not often included in the general photographer's lens kit. They create such a wide viewing angle that the image may look distorted because our eyes are not used to this kind of range. They are often used in event and architectural photography, for shooting in confined spaces. Wide-angle lenses, as it were, put the photographer in the center of events, making him no longer an observer, but a participant, creating the effect of presence. They are not very suitable for portrait photography, as they increase the perspective so much that facial features can be distorted and look unnatural.

Wide angle 24-35mm

You'll find a lot of kit lenses here for full frame cameras, they start at 24mm when the angle is wide but the distortion isn't as pronounced yet. These lenses are widely used for reportage photography by documentary photojournalists because they have a wide enough angle to capture a large number of objects, and the distortion is not so significant.

Standard 35-70mm

It is in this range of focal lengths of 45-50 mm that the angle of view of the lens will roughly correspond to how our eyes see (excluding peripheral vision). I personally would like to use this range when shooting outdoors or when meeting friends in a pub or at a dinner table. A standard lens such as the 50mm f/1.8 is a great value lens and gives excellent results. A fixed focal length lens will always give best quality images than zoom. This is because it is built with a single purpose in mind. He does one job well and several jobs poorly.

Initial telephoto 70-105 mm

This range is usually the extreme range for kit lenses. It starts with telephoto and prime lenses for portraiture (about 85 mm). This a good choice for portrait shooting, as it can shoot close-up portraits without distortion, as well as get separation of the subject from the background.

Tele 105-300 mm

Lenses in this range are often used for distant scenes such as buildings and mountains. They are not suitable for landscapes, as they compress the perspective. Longer lenses are mainly used for sports or wildlife photography.

Step 3 - How does focal length affect perspective?

I already talked about this in the previous section, but to give you a better idea of ​​the effect of focal length on perspective, I took 4 photos of the same objects at different focal lengths and compared them. Three objects (soup cans) were in the same position 10 cm apart in each photograph. It is worth noting that the pictures were taken on a crop camera, so the focal length will be slightly larger.

Now let's talk about what the crop factor is. In essence, this means that if any lens for a full frame (EF, FX, etc.) is put on a carcass with a crop factor, then part of the image will be cut off. The crop factor will be approximately 1.6. In real terms, this means that if you shoot with a 35mm lens, you will get the same result as if you were shooting with a 50mm lens.

How it works is shown in the pictures below. This is actually a zoomed image, narrowing the angle of view of the lens.

Even lenses that are designed for crop cameras (EF-S, DX) will experience a similar effect, as focal lengths are always specified for full frame. It's just that these lenses at full frame will give a strong vignetting effect, since the image is not projected over the entire frame area.

That's all! And two completely different shots taken at different focal lengths. The first is at 24mm, the second is at 300mm (both on a camera with a crop sensor).

First of all, when choosing a video camera, you should pay attention to viewing angle, since it defines the area of ​​observation. In video surveillance, the viewing angle plays an important, fundamental role. It depends on camera lens focal length and the size of its sensor. A camcorder with a larger sensor, even at the same focal length, will have a large field of view. High detail images can be obtained with a narrow viewing angle, not only by increasing the resolution of the system. If the viewing angle of the camcorder is wider, then the detailing of objects in the frame will be worse.

The purpose of the experiment: to clearly show the dependence of the viewing angles of the video camera on the lenses used.

Consider examples for video cameras performing "survey" functions, which are positioned to capture " general form».

Outdoor video cameras with different lens focal lengths and a fixed sensor size. The cameras are positioned in such a way as to demonstrate the "general view" of the parking lot in front of the building.

For comparison, let's take the following camera models with fixed (non-adjustable) lenses that have different focal lengths:

3.6mm lens,

2.8mm lens,

With 1.9mm lens,

Matrix size: 1/2.9 inch - Sony Exmor

For a correct comparison process, we used all cameras of the same resolution of 2 Mp on the same 1/2.9-inch matrix - Sony Exmor CMOS (IMX323).

The height of all three chambers in the experiment is the same. This is the 3rd floor of an office building, about 10 meters from the asphalt. In order to more clearly view the width of the camera's viewing angles, it was aligned to the lower right corner. And from the left edge, with the help of the screenshots taken, you can compare the wide or narrow vision of the video camera horizontally. As a result of the experiment, three screenshots were taken.

Angle of view with 3.6mm lens

On the first screenshot taken with the PN-IP2-B3.6 v. 2.6.3 with a focal length of 3.6mm, on the left side of the resulting image we can see a truck parked in a parking lot and a fence to its left. The viewing angle is approximately 72 degrees.

Angle of view with 2.8mm lens

On the screenshot made with a video camera with a focal length of 2.8mm, model PN-IP2-B2.8 v.2.6.3, about 15-20m of the fence is visible on the left, and part of the parking lot behind the truck. The viewing angle when using the camera PN-IP2-B2.8 v.2.6.3 with a focal length of 2.8mm is already about 87 degrees.

Angle of view with 1.9mm lens

The third screenshot was taken using a PNL-IP2-B1.9MPA v.5.5.2 video camera with a wide-angle lens with a focal length of 1.9mm. In the image, you can see not only the parking lot behind the parked truck, but also the exit of another truck from the parking lot. The viewing angle of this camera is approximately 112 degrees.

It should be understood that the wider the camera sees, the lower the pixel density and, accordingly, the worse the detail of each section of the resulting image.

Cameras with not the widest viewing angles have the right to life and are relevant in use, the main thing is to choose the right video surveillance camera that meets the requirements of the observed object and satisfies desired result by picture quality.

Calculation of viewing angles of video cameras for all 3 cases

a = 2arctg(d/2f),

a - viewing angle of the video camera, in metric degrees;
arctg- trigonometric function(arct tangent);
d - matrix width in millimeters;
f is the effective focal length of the lens in millimeters;

For PN-IP2-B3.6v. 2.6.3

a1=2*arctg*5.376mm/2*3.6mm = 73.4 degrees

For PN-IP2-B2.8 v.2.6.3

a2=2*arctg*5.376mm/2*2.8mm=87 degree

For PNL-IP2-B1.9MPA v.5.5.2

a3=2*arctg*5.376mm/2*1.9mm=109 degree

It can be visualized like this:

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It is rare that a photographer does not dream of a new lens. The reasons for this are individual. But here's how the focal length correlates with the compression of space in the frame and distortion, and why exactly this ratio should be put at the forefront when planning to buy a new lens or choosing from available ones, not everyone remembers and knows. Let's get acquainted with the opinion of a professional photographer. M.d. Welch is a special guest writer for Lensrentals.

Only after a few days of working on the article, I realized that when discussing lens models in detail and carefully, we completely forget about their character and behavior in general. Like many photographers, I have already lost count of the time I wasted reading and looking at reviews. I was wasting time saving up money for the "same" lens, but did not ask the main question - what will bring such a focal length to my photo?

As it turns out, I'm not alone. At Shooting the West in Nevada, I got to speak to a large group of photographers about differences in focal lengths and lens behavior. It turned out that many photographers, both beginners and experienced craftsmen, do not always realize why they are in different situations use one lens or another and don't understand that the choice shouldn't be based solely on the distance to the subject or the quality of the background blur.

In this article, I will not waste your time comparing the bokeh of different lenses and looking at frames pixel by pixel. I will try to outline some criteria for the focal length of the lens, see how the focal length correlates with the compression of space in the frame and distortion, and why this particular ratio should be put at the forefront when buying a new lens or choosing from available ones.

For me, the first criterion for choosing a lens is the compression of space in the frame, in other words - how much background should be present in the frame behind the subject. To clearly demonstrate the compression of space when portrait photography, I asked my good friend and fashion model Travis Stewart to work and not move until I took a few shots. I shot at different focal lengths, trying to get Travis to occupy the same part of each frame.

I started with wide angle lenses, gradually increasing the focal length. Focal lengths of 16mm, 24mm, and 35mm are rarely used for portraits, but pay attention to how much background gets into the frame in this focal range.

Travis, of course, is present, but the frame is not only about him, and such focal lengths are suitable when it is important to show not only the hero, but at the same time his environment, the place where he lives or works. Distortion or perspective distortion on these focal lengths is expectedly present (we will talk about it a little later), but even at 24 mm the distortion is not so strong as to ruin the picture. You can simply change the composition and, for example, shoot a full-length portrait.

Focal 50mm and 70mm are perfectly balanced: Travis is no longer lost in the frame, but stands out - he is "torn off" from the background, at the same time there is a considerable part of the landscape surrounding him. These focal lengths are also suitable for cases where you need to show the hero in the environment.

At 100mm, the background is compressed so that the mountain range disappears from the frame, and only the hills directly behind Travis remain visible. At 135mm and 200mm the hills seem to get closer. At these focal lengths, the hills appear to be directly behind Travis, although they are actually 800 meters away, if not more.

Distortion is another criterion by which you need to evaluate focal lengths. On the shots taken at focal lengths of 16 and 24 mm, you can see how much she changes the face of the model. For greater clarity, I made a series of facial portraits - the distortion will be more noticeable on them. At wide angle, the distortions make Travis' nose look bigger and his body and face appear to shrink and shrink. At focal lengths of 50 and 70 mm, distortion is reduced, the nose returns to normal size, and the body confirms that the owner spends a lot of time in gym.

It is because of distortion that most portrait photographers refuse wide-angle lenses. But here is an example for you when distortion can help and work for your idea.

I asked Travis to hold a bottle of water in front of him and took a series of shots. At a focal length of 16mm, the water bottle looks huge, it becomes the main object and the center of attention of the frame. At a focal length of 200 mm, the size of the bottle is not at all large and does not attract much attention. Imagine that you have two orders: one from sports team, the second - from the manufacturer of sports equipment. An image of an athlete holding the ball with his arm extended towards the camera is required. By choosing the wrong focal length, you can completely misplace the accents in the picture. A wide-angle or close-to-wide-angle lens will make the ball bigger and draw attention to it - the ball manufacturer will be satisfied. The telephoto lens focuses on the athlete, albeit with the ball in his hand.

Of course, you should not forget about the ratio of the depth of field and the focal length of the lens. Look at the examples - the depth of field decreases as the focal length of the lens increases. All shots were taken at f/10. The distance from the camera to the subject has a significant effect on the depth of field. In our case, even at 16mm, the background is blurred due to the distance from the camera to Travis.

It is unlikely that I discovered something new, but it was useful to experimentally check how the focal length of the lens affects not only distortion and depth of field, but also the space in the frame. As a result of this exercise, I now use two lenses with a fixed focal length as portrait lenses - 35 mm and 100 mm.

It is these criteria that should be used when choosing or buying a lens. If you are working in a small studio or indoor environment, a telephoto lens will not only help reduce distortion and provide good background blur, but will also compress the space around the subject. When photographing the owner of the enterprise against the background of the assembly line, it would be wiser to use a lens with a focal length of 35-70 mm to show the object in his surroundings.

Looking at test charts and comparing the bokeh of different lenses is, of course, interesting, but if we are talking about work, then make sure that you place the accents correctly.

M.d. Welch,special guest writer Lensrentals

One of the most important quantities that characterize a lens is the focal length. Therefore, understanding this quantity plays important role when choosing a lens and getting the desired result when taking a photo.

First, let's define what a lens is. Lens- This is an optical system consisting of several elements (lenses) that forms an image. falling on the sensor (film) of the camera.

Optical center of the lens is a value that is equivalent to the sum of the optical centers of each lens included in the lens. It can be located both inside the lens and outside it.

Focal length is the distance from the optical center of the lens to the camera sensor.

Focal length is indicated in millimeters. Those. if your lens says, say, 35mm, it means that the distance from the optical center of this lens to the camera's matrix is ​​35 mm. Also, on old lenses produced before about the 50-60s, the focal length was marked in centimeters.

Attention: do not confuse the focal length with the rear segment (the distance from the sensor to the rear lens), these are completely different values.

Let's take a look at how focal length practically affects the composition of a shot.

Focal length affects several aspects:
- image scale (zooming in of shooting objects);
- viewing angle of the image;
- image perspective;
- background.

Let's consider each item in more detail. but before proceeding to consideration, I want to mention one important quantity, without which there will not be sufficient clarity in this matter, this sensor area(its geometric dimensions).

We know that different cameras have sensors with different geometric dimensions, these can be full-frame sensors 36x24 mm, ASP-C sensors 23.7 × 15.6 mm, and there may be very small sensors 5.8 × 4.3 mm or less, which are installed in soap dishes and smartphones.

With the same lens focal length, sensors of different sizes will have a completely different composition with different scale, angle of view and perspective. This issue is considered in more detail in the article about the crop factor.

Why is this happening? Let's illustrate:

The illustration schematically shows how the lens projects a real image onto the matrix, but what we get in the frame depends on the sensor area.

For example, on a full-frame sensor, we get a wider field of view than on an APS-C sensor, whose area is 1.5 times smaller.

This is where the concept of effective focal length comes from - the focal length in terms of the 35mm equivalent, i.e. at which the composition in the frame will be the same as when using a lens with a focal length for a full-frame sensor. This is for ease of understanding as there are many different sizes of sensors.

Focal length and zoom

The longer the focal length of the lens, the greater magnification of the object being shot, it gives and, accordingly, a larger image scale is obtained in the photograph.

For example, when shooting a tree with a wide-angle lens, we can capture it completely in the frame, and if we shoot the same tree with a telephoto lens, then only its fragment will fit into the frame. This is where the proximity effect comes from.

Focal length and viewing angle

The angle of view in the frame also depends on the scale of the image. The shorter the focal length of the lens, the greater the angle of view.

For example, if we shoot landscapes and panoramas, then a wide-angle lens is more suitable for these purposes, since it captures a larger viewing angle. And if we shoot wild animals, then a telephoto lens is more suitable for us, which will allow us to maintain a certain distance from the subject.

Let's look at examples of the dependence of the viewing angle on the focal length.

The angle of view is especially noticeable when shooting in a confined space, such as indoors. So even the difference between 17 mm and 20 mm is significant.

Focal length and image perspective

In addition to the angle of view, the focal length also affects the perspective of the image. human eye sees our world in a perspective that corresponds to a focal length of approximately 50 mm. Therefore, photographs taken with a 50 mm lens form an image that is more familiar to the human eye.

A wide-angle lens conveys perspective more clearly, since the scale of objects in the foreground and in the background will differ more from what a person is used to.

Telephoto lenses, on the contrary, tend to compress space. The scale of objects in the foreground and background differs less.

For clarity, consider the examples below:

Perspective is noticeable not only in landscapes. When shooting portraits, for example, it is also important to observe the perspective so that there are no perspective distortions on the person’s face, the nose does not seem larger than it really is, etc. Therefore, the classic portrait focal length for 35mm cameras is considered to be 85mm.

Focal length and image background

The dependence of the focal length on the background in the photograph is relevant for those who shoot portraits.

The shorter the focal length, and therefore the wider the viewing angle, the more details fall into the background of the composition. And with the same scale of the object being shot, which depends on the shooting distance, we will get a completely different composition, since the background will be different.

Also, the smaller the focal length, the closer you need to approach the object and vice versa. Note my shadow on the toy in the examples below, this is the result of me getting too close to it when shooting at short focal lengths.

Publication date: 19.01.2015

How does the size of the camera's matrix affect the angle of view of the lens?

This is the third part of the lesson about camera lenses. In the first and second parts, we got acquainted with the device and the main characteristics of the lenses. We talked about the fact that the viewing angle and focal length of the lens are the main characteristics in previous lessons. We already know that these characteristics are interrelated:

The shorter the focal length of the lens, the wider its field of view.

The longer the focal length of the lens, the narrower its field of view.

When a person uses his own camera, he eventually gets used to the fact that at certain focal lengths, his lens gives one or another viewing angle: “brings” the scene being shot stronger or weaker. Will these ratios between focal length and viewing angle remain the same or change if the camera is changed? Today we will find out. Often, when discussing pictures, photographers say: “this picture was taken at such and such a focal length,” thereby characterizing the angle of view at which the image was taken. Even under photo examples in our articles, the focal length of the lens on which these images were taken is often indicated. How do you know what focal length on your camera corresponds to the same viewing angle? How to take a photo with your camera?

We have to figure out how the angle of view of the lens will depend on the model of your camera, get acquainted with the concepts of “crop factor” and “equivalent focal length”.

Excursion into history

Earlier, in the film era, 35 mm film was the most widely used - an ordinary photographic film familiar to every person. It was used everywhere, from the simplest compact cameras (probably everyone had a film “soap box”), ending with serious professional equipment. Since all devices had the same area of ​​the photosensitive element (film frame), lenses with the same focal length on all devices gave the same viewing angle. For example, on any camera working with 35mm film, a lens with a focal length of 50mm had a 45° angle of view. Recall that modern full-frame digital cameras also use a sensor that is equal in size to a film frame - 24x36 mm.

Lens viewing angle and sensor size

Today the situation has changed. matrices in digital cameras are of different sizes.

Therefore, with the same focal lengths of the lens on different cameras, the viewing angle will also depend on the size of the camera's matrix. Let's look at the diagram:

It turns out that if on a full-frame matrix (or on a film frame) a lens with a focal length of 50 mm provides a viewing angle of 45 °, then on an APS-C format matrix it is already 35 °. On a Nikon 1 system camera with an even more compact 1” sensor, the same lens will give a field of view of just 15°. The smaller the matrix in the camera, the stronger the lens with the same focal length will “zoom in”. The same lens, when mounted on different cameras, will give completely different picture. This must be taken into account when choosing optics.

Since sensors of completely different sizes are installed in various cameras today, it is easy to get confused with what angle of view a lens with a particular focal length will give on a particular camera.

Photographers of the old school, accustomed to working with film photographic equipment and classical meanings focal lengths, clearly associate them with specific viewing angles. To understand what focal length corresponds to a particular lens viewing angle on modern devices, two concepts were introduced: crop factor and equivalent focal length.

Equivalent focal length (EFF)

This characteristic is not needed for beginners, those who bought their first camera - the numbers of the equivalent focal length will not tell him anything. But for experienced photographers who are accustomed to film photography, this feature will be useful. It will also be useful to those who are thinking about buying a new camera with a matrix of a different size and want to choose the right optics for it, to find out how their old lenses will work on the new camera.

The equivalent focal length lets you know what focal length a lens with the same angle of view would have on a full-frame (or film) camera. This characteristic allows you to compare lenses of all types of cameras, including compact ones. In the specifications of a lens that is not designed for a full-frame camera, you can often find the item “equivalent focal length” or “35mm equivalent focal length”. This item is needed so that the photographer can figure out what angle of view this lens will give. For example, for a 50mm lens mounted on an APS-C sensor camera, the equivalent focal length would be 75mm. The tiny focal length of 4.3mm used in a compact camera lens matches the angle of view of a 24mm lens at full frame.

How to calculate the most equivalent focal length? To do this, you need to know the crop factor. This is a conditional factor that reflects the change in the angle of view of the lens when it is used with smaller sensors. This multiplier is derived when comparing the diagonals of digital camera matrices with a 24x36 mm film frame. The word "crop factor" comes from English words crop - "crop" and factor - "multiplier".

For example, the diagonal of an APS-C format matrix is ​​approximately 1.5 times smaller than a full-frame one. So the crop factor for the APS-C matrix will be 1.5. But the diagonal of the Nikon CX format matrix is ​​\u200b\u200bless than full-frame by 2.7 times. Therefore, its crop factor will be 2.7. Now, knowing the crop factor, we can calculate the equivalent focal length for the lens. To do this, you need to multiply the actual focal length of the lens by the crop factor. Let's say we need to know the equivalent focal length for a 35mm lens if it is mounted on an APS-C sensor camera. 35x1.5=50mm. So, the equivalent focal length of such a lens would be 50mm. That is, on an amateur DSLR, a 35mm lens will behave in the same way as a classic “fifty kopeck” on a full frame.

In further lessons, we will study what lenses are used when shooting various scenes, we will indicate their focal lengths both for cameras with an APS-C sensor and for full-frame cameras.

Sensor sizes and crop factor for Nikon photography

Nikon's modern system SLR and mirrorless cameras use only three standards of matrices of different sizes. They are easy to understand.

Full frame matrices(Nikon FX). They have a physical size of 36x24 mm, that is, they are equal in size to a frame from 35 mm film. Most modern lenses are designed for such cameras. And on them they can reveal their full potential. Among modern Nikon devices, full-frame matrices are equipped with: Nikon D610, Nikon D750, Nikon D800 / D800E, Nikon D810, Nikon D4 / D4s, Nikon Df. Since the matrix of such cameras is equal in size to a film frame, the concept of crop factor and EGF is not needed for such devices.

APS-C format matrices(Nikon DX). They have a physical size of 25.1x16.7 mm and a crop factor of 1.5. Such a matrix is ​​slightly smaller than a full-frame one, but it is much cheaper. Such matrices are sometimes called "cropped" (cropped). Almost all manufacturers of digital SLR cameras use this sensor size. Among modern Nikon devices, APS-C matrices have cameras Nikon D3300, Nikon D5300, Nikon D5500, Nikon D7100. You can still use full-frame optics with them, however, all lenses will “zoom in” much stronger, which is not always convenient, because some lenses are designed for a strictly specific type of shooting and the loss of the desired viewing angle prevents them from being used for their intended purpose. First of all, this applies to wide-angle, portrait and reportage optics. Full-frame wide-angle optics lose their main advantage - a large viewing angle; portrait full-frame lenses on the “crop” start to get too close, and it becomes difficult to shoot on them, you have to move very far. For example, setting the classic portrait lens with a focal length of 85 mm on a cropped camera, you will have to move away from the person being photographed by 5-7 meters in order to shoot at least a waist-length portrait. Full-frame reportage optics (primarily zoom lenses with a focal length of 24-70 mm) get uncomfortable viewing angles on the crop, which are not very suitable in practice for fast, dynamic reportage shooting.

To create lenses suitable for these tasks, specially designed lenses are produced for crop. In the Nikon system, such lenses are marked with the letters “DX” in the name. Since these lenses are designed to be used on a smaller sensor, they themselves become smaller and cheaper than their full-frame counterparts.

For the same reason, they will not be able to work correctly on full-frame mothers. What happens if you put a cropped lens on a full frame camera? Unlike Canon cameras, Nikon has such an opportunity. In this case, you will get a very strong darkening at the edges of the frame. By the way, modern full-frame Nikon cameras can recognize “cropped” optics if installed, they automatically crop the frame to the size of the APS-C matrix. This setting can be turned on or off in the camera menu.