The focal length of a lens is one of the most important characteristics of photo optics. Photography for dummies - what is the focal length of the lens

Lens - essential element any camera. And the focal length is the most important characteristic of the lens. However, for beginner amateur photographers with this characteristic, there is complete confusion. They cannot understand: for example, a lens with a focal length of 24-70 mm on a full-matrix camera is good or bad? And 15-44 mm on a "cropped" SLR - is this normal or not enough? And 7.1-28.4 mm on the "soap box" - is it very little or is it still possible to live? Well, let's figure out what the focal length of a lens is in general and what its various values ​​mean. A lens is a system consisting of several lenses. The image of the object being photographed enters the lens, is refracted there and reduced to one point at a certain distance from the back of the lens. This point is called focus(focus point), and the distance from the focus to the lens (lens system) is called focal length.

Now about what these or those values ​​of focal lengths purely practically mean. Initially, let's agree that we are now talking about a lens designed for shooting on a full-matrix camera (in this article we talked about what a "full matrix" is). Let's take a purely practical look at how the frames made with one or another focal length differ. We shoot from one point and change focal lengths from 24 to 200 mm. Focal length 24 mm.
Focal length 35 mm.
Focal length 50 mm.
Focal length 70 mm.
Focal length 100 mm.
Focal length 135 mm.
Focal length 200 mm.
Obviously, the smaller the focal length, the more fits into the frame, and the longer the focal length, the closer the lens brings distant objects closer. Short focal lengths are used for shooting all kinds of landscapes, architecture, large groups of people. Large focal lengths are used for shooting, for example, animals and birds, for sports shooting when you need to catch close-up some spectacular scene. The focal length of 50 mm is approximately the same as the field of view of the human eye (46°). Lenses with a focal length of less than 35mm are called wide angle lenses. With their help, it is convenient to shoot nature and architecture, but it should be borne in mind that the wider the angle (the smaller the focal length), the greater the distortion caused by the laws of optics will be present in the pictures. For example, if you shoot high-rise buildings with a lens with a focal length of 24 mm, then closer to the edges of the frame, the buildings on the right and left will look tilted - here's an example.
Lenses with a focal length of less than 20mm are called ultra-wide angle lenses and they distort the image a lot. (There are more separate view fisheye lenses). Here is an example photo (from here) taken with a wide-angle fisheye lens with a focal length of 8mm.
Lenses with a long focal length are called "long focal lengths", and those with very long focal lengths are called "telephoto lenses". In general, the classification there is approximately as follows: Lenses come with a fixed focal length (the so-called "fixes") and with a variable focal length (the so-called "zooms" from the word zoom, approximate). As a rule, lenses with a fixed focal length shoot better (and cost less) than a zoom set to the same focal length. That is, for example, in the general case, a 24 mm wide-angle will give better quality than a 24-70mm zoom set to 24mm. (There are exceptions, but we will not get into this jungle now.) And now we have come to a very important issue. And what about such a strange range of focal lengths on my Fujifilm X20, you may ask? It says 7.1-28.4 mm. Is it like a super mega extra wide-angle? No. The fact is that when we talk about cameras with a cropped matrix, the physical focal length of the lens does not change there (it cannot change), however, since it fits noticeably less in the frame on the crop, it turns out that the "angle of view" of the lens narrows, and accordingly, for a given matrix, the focal length will be different, as it were. It is "as if different", because if the lens has a focal length of 50 mm, physically it will remain so on any matrices. But the frames will be different. Now I will explain. Suppose we have a lens with a focal length of 50mm. It forms a round image, which, superimposed on a full-size matrix, gives us a full frame - there it is, marked in the illustration.
We put the same lens on a camera with a cropped matrix - for example, with a crop factor of 2. How will a frame taken with the same lens look like? It will appear within the bounds of the blue box in the illustration. That is less. And less - the object will be closer, so it turns out that when shooting with a lens with a focal length of 50 mm on a camera with a crop factor 2 matrix, the focal length will be equivalent to shooting with a lens of 100 mm (50 mm times the crop factor) on a camera with a full size matrix. The problem is that on the lenses of cropped cameras, it is usually the physical focal length of the lens that is indicated. And in order to understand what these numbers generally mean, you need to multiply the indicated focal length by the crop size - then you will get the focal length (zoom distance) numbers in the equivalent of a full-matrix camera (35mm matrix) and begin to understand what range of focal lengths is present in this camera. Example. Fujifilm Finepix X20 camera, zoom range - 7.1-28.4 mm. The crop factor of the matrix of this camera is 3.93. So we multiply 7.1 by 3.93 and 28.4 by 3.93 - we get a range (rounded up) of 28-112 mm in 35 mm equivalent. In general, the most common range for a digital camera. Second example. Amateur DSLR with kit lens. The lens has a range of 18-55mm. The crop factor of the matrix is ​​1.6. We multiply - we get 29-88 mm. The ranger is very so-so, but you can use it. Thus, in order to clearly imagine exactly what focal lengths are available in your camera (or in the camera that you are going to buy), you need to multiply the focal range numbers indicated on the lens by the crop factor - this way you will get data on focal lengths of 35- mm equivalent, which will be quite clear to you. It is clear that for full-length cameras with their "native" lenses, no recalculations are necessary. By the way, sometimes for the convenience of users, manufacturers write on non-replaceable camera lenses both their physical focal length and its equivalent for 35 mm - this is how, for example, the Sony RX10 camera, where the physical range is 8.8-73.3, and on the installed 2.7 crop produces an excellent range of 24-200 mm: from a good wide-angle to a very decent telephoto lens.

A camera lens is a system of lenses and one of its main characteristics is the focal length.

In order to deal with the question of what is the focal length of the lens and what it affects, you will have to remember a little physics.

So, the rays of light, reflected from objects, pass through the lens of the objective (not one, but several lenses are installed in the lenses, but for now we will not complicate it). Since the object being photographed is usually located at a considerable distance from the lens, the rays of reflected light can be considered parallel to each other.

When passing through the lens, the rays are refracted and at some distance from it they "gather" into a point. This point is called the focus, and the distance from the focus to the lens is called the focal length. The plane that is perpendicular to the main optical axis of the lens and passing through the focus is called the focal plane. An image is formed on it.

The figure shows an ideal situation, but nevertheless we will proceed from it.
In fact, the whole principle of “transferring” a real image to a camera matrix can be represented like this:

We can say that the focal length of the lens is the distance from its optical center to the camera matrix, that is, to the plane on which the image is projected.

This is what we have considered physical meaning the concept of “focal length”, but if you do not go into the details of optics and generally forget about physics, then the focal length determines how much the lens will be able to “zoom in” on the subject. Therefore, you can remember one simple rule:

the longer the focal length of the lens, the visually closer will be the object being photographed in the photo

Focal length is measured in millimeters and is usually indicated on the camera lens.

Various frame coverage angles

The field of the frame covered by the lens can be expressed as the angle of coverage of the field of the frame. Typically, for 35mm film, focal lengths of 40mm to 60mm generally correspond to the picture that the human naked eye perceives in perspective.

Lenses with shorter focal lengths than this standard range of focal lengths are called "wide-angle" lenses, while lenses with longer focal lengths than the standard range are called "telephoto" lenses. The shorter the focal length, the wider the frame coverage angle becomes (hence the name "wide-angle"), and the longer the focal length, the narrower the frame coverage angle (for "telescopic" lenses).

* The relationship between focal length and field of view angle is always constant, regardless of the lens focal lengths used. However, in exceptional cases, due to different design principles and distances from the camera to the object, the angles of coverage of the frame field may differ.

perspective

The lens displays nearby objects as larger, and distant objects as smaller. When using a wide-angle lens, the focal length is shorter, and this effect is enhanced, i.e. close-up objects are shown large, and distant objects very small (enhanced perspective).

When working with telescopic lenses, the opposite effect is observed, that is, distant parts of the plot are reproduced somewhat more, and close parts are somewhat smaller than is perceived by the naked human eye (flattened perspective).

Depth of field

When focusing the lens from a certain distance, there are areas in front of and behind the subject, which are also displayed sharply. This range is called the sharpened space range. If it is small, they say "shallow depth of field", and if it is large, they say "large depth of field".
The range of sharply displayed space becomes smaller as the set f-number decreases (i.e. when the f-stop opens!), and vice versa. In addition, with the same distance setting, the depth of field is the smaller, the longer the focal length of the lens.

Comparison of a zoom lens and a fixed focal length lens

The zoom lens is versatile

A variable (adjustable) focal length lens allows you to smoothly adjust the focal length without changing focus. In this case, the capabilities of a whole group of lenses with a constant focal length are combined in one single lens.

Lenses with fixed focal length and maximum image quality

A fixed focal length lens can be optimally applied to its specific area, combining compactness with exceptionally high image quality. Tamron offers a range of prime lenses that successfully take advantage of technologies originally developed for zoom lenses.

• Ultra wide angle lens (AF 14mm),
• Macro Lens (90mm F/2.8 1:1, 180mm F/3.5 1:1),
• Fast Telescopic Lens (300mm F/2.8),
• Reflex lens (500mm F/8) (supplied as a manual focus lens only).

Macro (close-up shots)

Dedicated macro lens

The macro lens (MACRO) is optimized for photographing small objects as large as possible. MACRO lenses correct for display errors that are more pronounced when shooting at close range.

Display scale

The display scale is expressed as the ratio of the original size of the displayed object (1) to the size of its reproduction on film (1/X) in numbers: 1:X.
How more number X, the smaller part of the original object is displayed on the film. The coin displayed on the film with the same size as in reality (life size) is reproduced in the display scale 1:1. A display scale of 1:2 means that it appears on film only at half its true size.

Close-up with a ZOOM lens

As mentioned above, macro photography is a method of displaying small objects in a photograph. Close-ups are possible not only with special lenses, but also with telescopic lenses that have a variable focal length (ZOOM lenses), provided that the telescopic lens has the appropriate setting. Tamron lenses with the designation "MACRO" on the barrel allow you to get a display magnification of at least 1:4.

solar hood

With the exception of a few models, most Tamron lenses come with a solar hood (also incorrectly referred to as "Back Light Hood"). These Tamron solar hoods are an essential component in optical rendering and are essential for suppressing unwanted stray light and loss of contrast. This applies not only to fixed focal length lenses, but also (to a greater extent) to zoom lenses, where the shortest focal length serves as the starting point for optical rendering of the image.

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Good afternoon friends! Gradually, we are approaching the key concepts in photography (we are talking about), without understanding which further advancement in teaching photography and generally conscious shooting is unthinkable, and this is what gives good stable results. Let me give you a quote about following the rules in photography:

Failure to comply with this rule - gives garbage.
The ability to follow this rule - gives a reliable crafting level.
The ability to break this rule - gives masterpieces.

So I think that beginners should strive to master the basic techniques and develop basic shooting skills (confidently shoot in manual mode, understand how to compose a frame, what to focus on in a frame, how to process pictures ...). And a confident base and experience will definitely bear fruit in the form of more interesting results, don’t even hesitate!)

The concept of lens focal length

Focal length is one of the most important characteristics of a lens. In short and simply, this parameter determines how close an image we can get. Choosing a lens should start with this, because your shooting style requires certain focal lengths.

I assume that you are already, which we considered earlier. Pay attention to the following diagram of a SLR camera:

Here, the red dotted line indicates the optical axis of the lens, in fact, its center. Here we are looking at a camera with a cut-away lens, top view. If you turn the lens with the front lens towards you, mark (mentally, of course!) The center of the circle, then, drawing a perpendicular down from it, you will get the optical axis. The object being filmed is marked green on the left. The red lines represent the passage of light through the lens.

Every lens has a lens that flips the image. The point of intersection of the rays in it is called the optical center of the lens. The figure is marked by the point of intersection of the lines.

Hold your attention on this diagram for a moment and take a closer look. There is nothing complicated in this, it is enough to delve into it once.

Focal length is distance from the optical center of the lens to the focal plane (matrix). See schematic drawing above.

The exact location of the optical center is known to the lens developers. And the point that corresponds to the focal plane, i.e. matrix, can be identified by the designation of a circle with a straight line intersecting it on the camera body to the right of the wheel that switches shooting modes (on Nikon).

Naming. In the speech of photographers, you can hear the following names:

• focal length;
• focal;
• FR (abbreviation);
• focal length (English equivalent);
• FL (abbreviation of the English equivalent).

What is focal length measured in?

Dimension in millimeters, mm. It's better to look at an example. Let's say we have the popular Nikon 35 mm f/1.8G AF-S DX Nikkor lens. The marking indicates 35 mm, i.е. its focal length is constant and is 35 millimeters. Don’t pay attention to the rest of the characteristics yet, we will consider them when we talk about lenses.

Another example is the standard Nikon 18-55 mm f 3.5-5.6 GII VR II AF-S DX Nikkor kit lens. It says 18-55 mm, the focal length is variable. That is, by turning the zoom ring on the lens, you can change it from 18 to 55 mm. Looking ahead, such lenses are called zoom lenses or zoom lenses.

Popular misconception. Sometimes you hear that the focal length depends on something. This is not true. As described above, the focal length is physical characteristic lens, which is incorporated by the designers. It does not change under any circumstances.

What does focal length affect?

Attention! We are approaching a critical part of our conversation for understanding. If you understand what will be discussed below, then you will make yourself an excellent reserve for understanding the composition, which is extremely important. If not... You can't help but understand! In which case, I am always at your service in the comments.

Parameters affected by focal length:

1. viewing angle;
2. Image scale;
3. The degree of blur and depth of field;
4. Perspective (indirectly).

Let's consider everything in detail. Small conventions - in the article on matrices, we considered . There we talked about the fact that the viewing angle is wider, the larger the matrix. Here we will take a certain size of the matrix and we will consider all changes in the parameters based on the fact that the matrix does not change. In order to avoid confusion in different focal lengths depending on the size of the matrix, we adopted the EGF (effective focal length), which recalculates the focal length in the equivalent of a full-frame camera. We will talk about this in the next article on the crop factor. All of the following examples are from a crop camera, i.e. if the same shots were taken with a full-frame camera, the angle of view would be wider.

Effect of focal length on viewing angle

As the focal length increases, the viewing angle decreases, and vice versa, the smaller the focal length, the wider the viewing angle. Look at the examples - shot from the same point at different focal lengths.

It can be concluded that:

• The more surrounding space we want to capture in the frame, the more wide-angle (with a smaller focal length) the lens should be.
• Conversely, if you need to shoot a relatively distant subject, then it is better to prefer a telephoto lens (with a long focal length).

Effect of focal length on image scale

In fact, it is related to the first point. The fact is that with a larger focal length in the final picture, the object being shot will turn out to be larger. It is said that such a lens will give more magnification or a larger image scale.

An example - we are standing on one point, not moving, and we are shooting a person at a distance of 10 m with a wide-angle lens with a 18 mm focal length. We get a photo of a person in full growth and a lot of space around the edges. By changing the lens to another, for example, with a 85 mm FR, we will also get a full-length image of a person, but now there will be less empty space around the edges, and the person himself will be larger. As a result, we will get an image on a larger scale.

Influence of focal length on the degree of blur

It is quite possible that you have already heard about this and know that the longer the focal length, the more blurred the background will be. This is why portraitists love telephoto (long focal length) lenses so much. Look at the example of the toy, how the blur changes:

It is worth mentioning that as the focal length increases, the depth of field (DOF) will become smaller, thereby forming a blur. Just keep this in mind, we will talk about IPIG a little later.

For some beginners, a DSLR (or mirrorless) is associated with the possibility of a strong blur of the background, which they do when they “grab” such a device. In fact, blurring the background "in the trash" is not always useful. Yes, so we have all the attention focused on the object being shot, but there is nothing else in the picture! In many cases, it is better that the details of the background still be traced. And an important role in this is played by the correct choice of focal length.

Effect of focal length on perspective

First of all, what is perspective? This is the nature of the transmission of the ratio of the size of the object being shot and other elements in the frame, its shape. Consider the following shot taken with a 17mm (wide angle) lens:

There are road barriers and houses in the distance. In the case of shooting with a wide-angle lens, we get interesting geometric relationships- the scale of the fence will be noticeably larger than the house on the horizon. This is unusual for the human eye, and allows you to build interesting compositional solutions.

In the second case, shot at 125 mm (tele-focal range), the difference in scale between the fence and the house will be less.

In general, when shooting objects from one place with different focal lengths perspective will not change.

The focal length only affects perspective if objects close or far are in the frame. In the example above (1st photo), you can see that there is a fence in the frame, located close to us. Being close to us, the fence is depicted in the frame large, and the houses in contrast seem small. Therefore, we see as if the perspective is stretched. Another example is if you shoot a distant object with a long-focus lens, and there is another object much further away from it, it will seem as if there is a minimum distance between them, and they are nearby. As they say, a compressed perspective. This is due to the fact that the photographer is very far away from the object being photographed, and the difference in the scale of the object being photographed and the very distant background is not so great. This is also seen in the example above (2nd photo). The fence is far away, the house is very far away, but it seems that the distance between them is not too great.

Wide-angle lenses with short focal lengths are great for landscape photography. But at the same time, they are not recommended for use when shooting portraits, because the shape of the face will be more elongated and look unnatural. It is said that wide-angle lenses (with a small focal length) stretch the perspective, while telephoto lenses (with a large focal length) compress it. But this happens primarily not because of a change in the focal length itself, but because of the need to change distance between subject and photographer.

Handheld shooting at long focal lengths

Problem.

It can be considered an additional activity for those who want to know more) I propose to move on to a small photo-reasoning and consider a simple situation. In fact, such thoughts should be “scrolled” in your head all the time, very quickly you will get used to doing it automatically.

Let's say you shoot a close-up portrait in the evening with an APS-C camera. There is no sunset yet, but it seems that there may already be problems with the lighting, it is not enough. The goal is to capture a beautiful portrait with strong background blur.

In fact, if you study photography from scratch and read my articles consistently (see), then you understand that your knowledge is not enough. But there is nothing wrong with that - we will reason with what we have and gradually expand the horizon of the unknown) Do not worry, very soon the puzzle of knowledge will form in your head. Just don't be lazy to think.

Recently we talked about the matrix, (ISO). So, at the same ISO on a camera with a smaller matrix (we compare cameras of approximately the same generation and manufacturer), the picture will be noisier. Usually, the noise level of full-frame cameras is taken as a reference. It follows that it is very likely that our camera will be able to register less light with the same quality. Let me explain - shooting on a full-frame camera at ISO 1600, we get an image of a certain noise. When shooting on a camera with an APS-C matrix, in order to get the same level of noise, we already need to shoot, for example, at ISO 400. This means that less light will enter, which is clearly not a good factor in our conditions.

We need to achieve a strong blur. This can only be done with a telephoto lens with a long focal length. The degree of blur depends on other factors (for example, distance from the subject, aperture), but more on that later. Let's say we chose 105 mm. This is a fairly large focal length, and ...

The longer the focal length, the faster the shutter speed should be chosen. This will compensate for trembling in the hands and get a clear, not blurry picture.

Excerpt? What? Again, we will soon consider in detail. In short, this is the exposure time of the matrix, i.e. the time during which light hits the matrix after pressing the shutter button. Get used to the word "exposure") Now we come directly to the problem of shooting handheld with a lens with a long focal length.

You can make a comparison - imagine that you are at school and you need to point to a small detail on the board. What will be easier to do - a short pen or a long pointer? Of course, with a pen. The reason is that when using a pointer, the slightest deflection of your hand will result in a significant deflection of the opposite side of the pointer. Using a pen, even with a significant deflection of the brush, its opposite edge will not deviate so much. That is, using a long object as a pointer, we need to clearly fix the position of the brush.

It's the same with photography, only harder. Where we point on the board is our subject. The lens acts as a pen or pointer. Well, the brush remains the drive of this whole mechanism) It is important to understand that our strong grip on the camera, a comfortable stand and a short shutter speed (we reduce the exposure time of the matrix) act as a fixative here. Even if our brush moves to a significant angle, the shutter will work faster, and the matrix will no longer “see” this.

Let's say we shoot at a long shutter speed for these conditions. What's happening? Light from a point on a person passes through the lens and hits the matrix, forming the same point. Our hand trembled a little, the camera shifted upwards, and the light from another point on the person falls on the same point of the matrix. And at this time the matrix continues to be exposed. As a result, we get a blurry image, in the common people “shake”. If the shutter speed were shorter, the result of the shift would not be fixed on the matrix, and we would get a clear photo.

So what's the answer? And it is very simple - you need to find a balance, the optimal ratio of all parameters. Minimize problems and achieve the maximum possible result. Something it reminds me of university times) We will learn this.

What you need to remember about focal length?

What it is and what it affects, I think you already understood. Now briefly to repeat the basic information:

1. Focal length - the distance between the optical center of the lens and the camera matrix.
2. Often referred to as FR for short.
3. Measured in mm.
4. The focal length is determined by the lens designers and does not depend on the camera on which the lens is mounted.
5. Affects the viewing angle and zoom level, allowing you to "zoom in" or "zoom in" on objects.
6. Affects the degree of blur and depth of field.
7. Affects the perspective of the image.
8. At longer focal lengths it is more difficult to shoot handheld.

The focal length greatly affects the final result, so it is important to learn how to “feel” it and choose the right one for specific purposes.

I suggest you go outside and try to shoot, for example, landscapes with different focal lengths, being at the same point. And observe how objects approach, how geometric relationships change. Shoot close objects, such as a tree branch. You can not even shoot, but simply change the focal length (if you have a zoom lens) and observe the changes in the viewfinder.

Over time, you will get so used to your camera and lens that you will offhand, without looking into the viewfinder, determine what approximately the result will be.

Good luck and see you soon!

4 comments on What is focal length? What does it affect?

Hello Vlad! I read your lessons on photography, I really liked the articles about the device of the camera, everything is consistent, understandable and intelligible. Thank you for such a presentation of the material, I will wait with interest for the continuation 🙂
Maybe you will make a brief announcement on what other topics to expect articles? And what materials do you think are useful for a beginner to learn? And then there are so many things, you won’t immediately understand what you need to deal with in the first place)

• Good evening, Catherine!
  Thank you very much for appreciating my work, it's always a pleasure to receive such feedback :) it looks like it was useful for someone!

  1. Regarding the announcements - on the horizon are materials about crop factor, aperture, shutter speed, ISO, exposure, dynamic range and ... Perhaps, I will not reveal the cards further)

  2. With regard to materials that would be useful for a beginner to study. First you need to understand at what point the person is, i.e. what he knows at the moment and where he wants to get (what results to achieve) and, based on this, plan the best steps to overcome this path. Tell in in general terms what you know at the moment and what you are striving for (what genre of photography attracts you the most and what works inspire you).

  Generally speaking, in my opinion, a beginner needs to conduct an educational program for himself on critical aspects. These include the triangle of aperture, shutter speed, ISO, have an understanding of exposure, focal length, depth of field, shooting modes (shutter / aperture priority or manual, it’s better not to shoot in “Auto”) + basic aspects of composition. In general, having a superficial understanding of all this, I would further advise to shoot-shoot-shoot as much as possible.

  At the same time, pay attention to the surrounding space from the position of the “viewfinder”. For example, go to work and, watching how the light falls on the flowers, think about what angle they would look best from, how you would crop them ... In parallel with the practice, close the gaps in the basic theory of photography, look at many photos of other people and reflect on how and under what conditions they were filmed. The last one is very important. Trying to shoot in RAW format, you can even start right away, especially if you have editing skills. RAW provides tremendous editing possibilities, "forgiving" many mistakes.

  You definitely need to learn how to process photos - I'm not a supporter of imposing a ton of processing on the original frame, but I think that doing basic things (exposure compensation, noise reduction, sharpening, working with shadows / lights, color correction, noise elimination, etc.) should be carried out, because. to. give a significantly better perception of the final photo. For my part, I can recommend Lightroom.

  And gradually move on to more advanced things, but by that time the “newbie” will already be able to tell and show a lot of interesting things and understanding what to do and where to move on will definitely be. For basic things, for example, I recommend reading the articles on Alexander Shapoval's website, he expounds perfectly. And don't forget that practice is everything.

  As far as my plans are concerned, this moment I have a desire to collect something like a textbook - a consistently written manual, after reading which a beginner in photography could get comfortable, learn how to get good results and critically approach the analysis of his/other people's photos, most importantly, learn to think. Plus, he knew how to process his pictures, easily understood them when there were a lot of them and just loved photography)

  It is difficult to paint it all at once, it takes a lot of time. But gradually, materials in chronological order for study will be added to the Lessons section (so far only technical ones, about processing later) + I periodically make collections of Friday Mood, where I present thematically the work of other photographers that inspire me and seem interesting.

  P.S. To keep abreast of emerging materials, if you wish, I recommend subscribing to email newsletter or the VK group in the upper right corner of the site. And, of course, if you have any questions, feel free to contact me in the comments or here. I will try to answer as much as possible.

Focal length

Focal length is the distance from the optical center of the lens to the focus point (in mm), i.e. to the film (matrix), where a sharp image of the object is formed. For example, focal length 50, or 120 mm. And what, exactly, is the difference? The difference lies in the choice of frame boundaries. Let's see what pictures can be taken from the same shooting point: the photographer does not move, but changes the focal length of the lens (or changes the lenses themselves on the camera).

focal length 24 mm, 30 mm, 50 mm, 120 mm, 180 mm, 300 mm

shooting was carried out from a distance of 15-17 meters (from the window of the 4th floor of an ordinary five-story building), 2 lenses were used: a wide-angle zoom from Pentax, and a long-focus Soviet lens Granit-11m

In general, everything is not difficult: the more we increase the focal length, the more we bring the subject of photography closer (or, conversely, reduce it). Even simpler: what is more than 50 mm, we increase, everything that is less than 50, we reduce. And, quite simply: a focal length of 100 mm is a 2-fold increase, 180 mm is an increase of 3.6 times. Easier nowhere. But why was 50 mm chosen as the reference point? It is generally accepted that such a focal length corresponds to the angle of view of the human eye (in fact, the peripheral vision of the eyes covers a much larger angle). They also consider that a standard lens has a focal length of 50 mm, since this is close to the diagonal of a film frame (43 mm). Do not look for difficulties in this. Sometimes they are created only in order to successfully overcome them later :)

How to find the focal length of a lens

This has already been discussed in the article "Lenses", we will repeat for those who came here from other pages. How to find the focal length? Very simple. The focal length is indicated on the barrel of the lens, next to it is indicated its aperture. In the photo on the left, we see the old Soviet Helios 44k-4, which has a focal length of 58 mm and f2 aperture (marked 1: 2). I indicated the focal length in the photo with a yellow arrow.

What else can you tell about the lens, looking at its designations? A little.

This model of Helios has a "K" bayonet mount (it will fit a Pentax DSLR without any adapters), multilayer coating, a fixed focal length of 58 mm, f2 aperture, a mounting thread for filters - M52x0.75, the lens itself was produced for Zenith cameras with a "K" mount "at the Krasnogorsk Mechanical Plant, the latter is indicated by the icon of a prism with a refracted beam ... You can, of course, tell much more about this optics than its designations say - but this is beyond the scope of the article about the focal length ...

What is zoom

I already mentioned in the article "How to choose a camera" that this characteristic is often mentioned in stores. Actually, what is zoom? A zoom is a lens with a variable focal length, it is also a "zoom", it is also a "vario lens" - there are many names, but the meaning is the same. To be more precise, the complete absence of such :) For example, we have a typical focal length of the lens 28-55 mm. Divide 55 by 28 and get approximately the number 2. This means a 2x zoom :) This figure is absolutely of no use, because, for example, a 100-200 mm zoom lens also has a 2x zoom, but these are completely different lenses , with a different angle of view and for completely different tasks. In this regard, only the focal length is a useful characteristic, so let's return to studying it, and forget the marketing word zoom, or we will use it not for meaningless calculations, but only to designate a zoom lens. That's why:

A zoom is a lens that has a variable focal length. And no more!

The zoom, of course, is convenient, but in the red at the long end of the zoom, the aperture ratio almost always drops (especially with cheap optics). For example, a compact lens says 5.8-24/2.8-4.8. The last two digits indicate the lens aperture, at the short end it will be 2.8, at the long end, respectively, less - 4.8. Those. as the focal length increases, the aperture will fall! Therefore, one small tip: do not chase a huge zoom! There are digital compacts (we read - a small matrix!), With a 20-30x (and even more) zoom. And here, when shooting at the long end of the zoom, the lens aperture closes abruptly, as a result, less light enters. This means that fast shutter speeds will become unavailable, and shooting at long shutter speeds (not using a tripod) will lead to shake and blurry shots; either automation (or you) in response increases the sensitivity of the matrix, i.e. increases the signal on it, and the small matrix of the camera makes noise, but what is the result? Disgusting pictures. Therefore, choose a 3-4x zoom, otherwise, if you are not going to work with a tripod, it will be money thrown away!

It's not a zoom lens, it's a fixed focal lens, it's a discrete lens ... did I miss anything? Yes! He is a lens with a fixed focal length :) You have already seen the fix in the Helios picture above. Once upon a time, all lenses were fixed, the first zooms appeared in the 60s of the last century, for example, the Rubin 1ts lens, focal length 37-80, aperture 2.8, was a standard lens for the Zenit-6 camera.

The zooms of that time had an interesting salient feature- they did not lose focus when changing the focal length! Modern lenses are deprived of this: alas, you need to focus every time after zooming ... And this disgusting thing was done in the name of reducing the cost of production. Autofocus, of course, helps, but if manual focusing is necessary (and it is sometimes necessary!), Then one can only envy the wonders of ancient mechanics (and most importantly, attitude).

Focal length in 35 mm equivalent (EGF)

There are two focal lengths - real, and equivalent to cameras of 35 mm format. The real is indicated on the lens, the equivalent does not exist in nature, it is calculated. Why such difficulties and why is it necessary? The fact is that film cameras (35 mm format) have the same frame size: 24 x 36 mm, and therefore it was easy to compare their lenses. If one camera had a lens focal length of 50 mm (standard fifty dollars), then the lens, say, at 28 mm was called wide-angle, 70-100 mm - portrait, and over 100-150 mm - telephoto (or telephoto lens). This division was conditional, but it was understandable and suited everyone - some had a wider angle of vision, others had a narrower one. Actually, we are talking about the angle of view of the lens, it’s just that “bad” photographers confuse a beginner with terrible terms: “focal length”, “equivalent focal length”, “EGF”, “Matrix crop factor”, just “crop”, and other rubbish that has only a side relationship to the angle of view of photography, and hence the composition of the frame :) In general, in the era of 35 mm film, it was easier to compare lenses and take pictures, and not nonsense :)

Photographers are generally strange people. If you ask them - in what units the aperture is measured, then instead of a definite answer, you can hear a rather lengthy speech about the ratio of the focal length to the diameter of the active aperture of the lens. They measure angles not in degrees, but in millimeters, the angle itself is called the focal length, and the film is called 35 mm (and even 135 mm), although its frame size is ... 36x24. Where the hell did those 35mms come from? It's simple, let's not invent new standards, but rather try to understand the old ones.

What is 35 mm format? 35 mm is the width of the film including the perforated part.

Sometimes 35 mm film is referred to as type 135. The index 1 before the number 35 was introduced by Kodak in 1934 to indicate perforation (before that, the film was unperforated). Then other formats were offered, but they did not take root: 35 mm film replaced everyone. And only a separate niche is occupied by cameras of medium and large formats.

However, with the advent of digital cameras, the situation has changed. If digital cameras had the same matrix size - 24 x 36 mm, then there would be no difficulties in comparing lenses. But only very expensive professional-grade DSLRs have this size from digital cameras. Amateur DSLRs have a matrix size 1.5-2 times smaller than "full-size", and digital compacts are even smaller than amateur ones. Such cameras are considered non-35 mm format and, depending on the size of the sensor, are designated APS-C, 4/3, and others. Naturally, the smaller the matrix, the smaller the angle of view of the lens. Therefore, it became impossible to compare the same focal length if the cameras have different sensor sizes. To avoid confusion, we decided to introduce the term "equivalent focal length" (EFF), i.e. focal length for cameras of 35 mm format - to compare with a photographic film having a width of 35 mm and a frame size of 36x24 mm. As a rule, the actual focal length is indicated on the lens, and in the user manual you can find out which EGF it corresponds to. Sometimes this can be found in short description cameras in the store.

The focal length of the same lens does not change when mounted on a camera with a smaller matrix - the angle of view changes. But, if you like, the focal length of the entire system (matrix + lens) has changed.

EGF is used only to compare camera lenses with different crop factor - comparisons in the angle of view. The terminology here is as follows: if a lens with a focal length of 50 mm is installed on a matrix 1.5 times smaller than a full-frame one, then they say that the EGF has become 75 mm - the angle of view has become the same as if the focal length were 75 mm. It turns out that's what. Yes, the focal length of the entire system has changed (the lenses themselves have not!), but the distortions within this lens have not changed, since they were "sharpened" for 50mm, not 75.

On a smaller matrix - at the same focal length - the frame will be cropped, and the angle of view is smaller

If the size of the matrix is ​​known, then the equivalent is easy to calculate. How many times the camera's matrix is ​​smaller than the film frame, then the real focal length must be multiplied by so much to find out the equivalent. This difference (more precisely, the multiplier) is usually called the crop factor of the matrix. For example, Nikon DSLRs have a matrix size of 23.7 x 15.6. If the wide side of the film frame (i.e. 36 mm) is divided by 23.7, then the crop factor (here by crop I mean the aspect ratio) will be approximately 1.5. You can also divide the other side: 24 by 15.6, there will be the same crop. This means that the actual focal length, which is indicated on the lens, must be multiplied by 1.5 to get the equivalent. For example, a kit lens (from the English KIT - kit) for Nikon has a real focal length of 18-55 mm. We multiply 18 by one and a half, and 55 by one and a half, as a result we get 27-82 in 35 mm equivalent. And what does it mean? Rejoice, this is a universal lens - there is a wide angle for landscapes, and on a long one you can at least shoot portraits! It’s a pity that the whale has a weak aperture, but that’s a completely different conversation.

The equivalent focal length is used to compare camera lenses with different crop factors.

Those. when the matrix of such cameras has an unequal size.

Table of crop factors for different camera formats

The Russian word "multiplier" has long been replaced by the expression "Crop factor", apparently to give your speech outlandish overseas shades, like, don't think that I'm from Russia, I'm like from the states :-) Let's look at the multiplier (or crop) for typical photosensitive sizes camera elements:

As for the compacts, they have matrices 4-8 times smaller than the size of a film frame! For example, a typical 1/2.5"" matrix has a size of 5.8 mm along the wide side, i.e. 6.2 times smaller than the 36 mm side of the film. The lens of such a camera with a focal length, for example, 5.6 - 17.7 mm, will correspond to 35 - 110 mm EGF. Let's take a SLR camera with a 1.5 crop and a lens marked with a focal length of 16 - 45 mm. After multiplying by 1.5, we get the equivalent focal length - it will be 24 - 67 mm. Now you can compare the lenses of these cameras - this compact has a longer focal length lens, and the DSLR has a wider angle. Whatever one may say, but all sizes will be compared with 35 mm film for a long time!

Focal length and lens types

More precisely, the equivalent focal length, types of photography and angle of view of lenses for 35 mm cameras. Here we clearly see how meaningless the word zoom, or rather the zoom ratio :) The focal length rules!

* macro photography depends more on the special properties of the lens than on the focal length.

For example, it’s good to shoot a landscape with a wide-angle lens: such optics have a higher depth of field, and more will fit at a wide shooting angle). wide angle important in a landscape, in an apartment, architecture, city, in any limited and unlimited space, and wherever it is required to emphasize the expressiveness or dynamics of the plot. And it is convenient to zoom in with a telephoto lens, i.e. zoom in on a hard-to-reach subject. For example, the muzzle of a lion in the wild and in the whole frame :) A wide-angle lens has a focal length of less than 35 mm, a standard 35-65 mm, a telephoto lens - from 65 to 300 mm and even higher.

A station wagon can have them all in one bottle, for example, 24-200, 35-105, 28-116 mm, etc., which is its main advantage. The disadvantage of all generalists is that they are inferior to a specialized one (for example, a telephoto lens), as a rule, in aperture ratio, or in maximum focal length, or in price (with the same aperture ratio, the price will be higher), or in quality.

A simple (nowhere easier!) The picture on the left will help you learn all of the above about the angle of view of various lenses. We clearly see how the focal length changes the angle of coverage of the frame, i.e. the scene or scene being filmed. This division is, of course, highly arbitrary. Landscapes are also shot with a long telephoto lens, and everything is shot with a wide-angle lens, even up to portraits.

It is clear that the choice of lens always depends on the tasks, creative preferences and even the mood of the photographer. Beginners can take a large zoom with a coverage of 28-200 mm (or 24-1000 mm, there is even such a one!), And end up with a huge choice of focal lengths, here you have wide-angle + standard + telephoto + very large telephoto, and all happiness in one vial.

Indeed, why bother with a selection of kilograms of additional optics! However, the disadvantage of this choice is a small aperture (especially at the maximum focal length), and optical distortion (aberration), alas, all large zooms have such disadvantages.

Focal length and aberrations

The greater the difference between wide angle and long angle, the greater the optical distortion of all kinds, called aberrations. Engineers minimize them by adding low dispersion and aspherical lenses to the optical design, but then the weight and price of the lens will be much higher. Moreover, aberrations are not eliminated until the end, they are simply made less noticeable, as much as possible. Therefore, a universal lens, solving some problems, gives rise to new ones :)

The best in this regard will be a fix - a lens that has a fixed focal length (it has only one). Distortion in this is easier to remove than in zoom. In addition, fixes are distinguished by greater aperture ratio, smaller dimensions, and the most worthy price / aperture ratio. And, nevertheless, the coverage of several focal lengths at once (which is what the station wagon does) attracts many ...

There are three main groups of aberrations: distortion (geometric distortion), chromatic aberration (color distortion) and, finally, diffraction (loss of sharpness at tightly clamped apertures). The most typical example for a wide-angle lens is distortion. The wider the angle and span of the zoom, the more the so-called. barrel distortion (if not corrected with additional lenses). To better understand this contraption, we look at the picture.

A very crooked photo at the edges is, of course, inherent in inexpensive lenses or fisheye optics, but not in crooked hands. Although ... how to say, cases are different. For example, crooked hands are not able to correct distortion either in Photoshop or in any other graphic editor!

Below is an example of geometric distortion (barrel distortion) of a very expensive Pentax DA 15mm f/4 AL Limited prime lens compared to a Pentax DA 16-45mm f/4 ED AL wide-angle zoom lens. A couple of test shots were taken from about two meters, with the same settings, and at the widest angle. The difference was only in the focal length: the fix has the only one - 15 mm, and this zoom has the widest - 16 mm, which is equal to 23 and 24 mm in the EGF, respectively. It is better to enlarge the pictures and see the distortion around the edges ...

focal length 15 mm (EGF 23 mm), Pentax 15mm f/4 Limited

Focal length 16 mm (EGF 24 mm), Pentax 16-45 mm f/4

The wider the angle, the more distortion. Since the Limited has a wider focal length, it was expected that there would be a little more distortion, or, in any case, a fight would flare up. But it did not work out: the fix won unconditionally! Its geometric distortions are minimal, while Pentax 16-45 has it, which is quite expected for any zoom (and quite acceptable for a zoom of this class).

Other things being equal, the most expensive lenses are those with a wide angle and, of course, telephoto lenses. But the most expensive of them will be fast, and, of course, dust and moisture-proof professional lenses with ultrasonic motors and reduced optical distortion. As a rule, such lenses are large and heavy, since they have more lenses in the optical scheme to eliminate aberrations.

Lenses with a focal length of a short range "around" 50 mm, they are also called "standard" or "normal" lenses, give less distortion. In addition to zooms, the standard ones also include some fixes, for example, "fifty kopecks" (focal length = 50 mm). The distortions of such fixes are the most minimal, and there is only one drawback (and very significant!) - there is no zoom. :)

One of the typical schemes of a fixed lens. Lenses of various shapes
designed to eliminate distortion.

It is worth mentioning that, in addition to the focal length, lenses can be divided into macro lenses and portrait lenses. Distortions of the first are removed in the minimum focusing distance, and the second in the "portrait" zone (in the region of 1.5-2 meters).

It must be remembered that on a cropped DSLR (APS-C format), the normal (or standard) focal length will not be 50, but 30-35 mm. Whoever doesn’t understand, we read again about the equivalent focal length :) If after that it’s not clear, then I advise you to choose a full-frame camera, where the real focal length is equal to the equivalent one, and you don’t have to recalculate one into another :)

The world's widest compact cameras.

What is the minimum focal length for digital cameras with fixed lenses (i.e. compacts)? In EGF, the wide angle of most models starts from 35-38 mm, i.e. it's not that wide. There are also those with a large viewing angle, for example, Nikon Coolpix 5400 - a minimum focal length of 28 mm, some Panasonic models have an even shorter focal length, for example, Panasonic Lumix DMC-FX37 - 25 mm. But you won't surprise anyone with such a wide angle.

But there are compacts with really wide-angle optics: a focal length of 24 mm (and even less!). Starting in 2010, I conducted a survey that looked like this:

"If anyone knows a compact camera with a wider angle (with a smaller focal length in EGF) - send the name of the model, I will indicate it on the site."

Here are the names of those who sent (as promised):

Yuriy Dzyubina from Ukraine, Sergey Baum from Moscow, Evgeniy Afonasenkov from Volgograd (he indicated 2 cameras), the author of this site (well, why not mention himself?), Roman Eltsov from Yaroslavl, who did not want to be called “shifted” and Andrey Andronov from the Volgograd region .

But since then, a lot of compacts have appeared that have a focal length of 24 mm, so I will not list all the models whose names were reported for the site by its readers. But I’ll still point out a couple of memorable cameras.

Samsung EX1, focal length 24 mm, 1/1.7" matrix, 10 MP, aperture f1.8 - f2.4, manual settings, weight 160 g. A camera with a very decent aperture and a rather big matrix for a compact! And the camera costs about 100 rubles per gram :)

KODAK EASYSHARE V570 with two built-in lenses(!). Wide-angle prime - focal length 23 mm, aperture f2.8. The second lens is a zoom lens with a focal length of 39-117 mm and a much weaker aperture: f3.9-f4.4. This double-headed digital camera also has 2 matrices, but it seems that there are no such settings as shutter speed and aperture ... But the solution is original. Weight 125 g. It could be even lighter and cheaper if you leave 1 wide-angle fix and remove the zoom - you would get an excellent landscape shot with an ideal price / quality ratio!

But there is an even shorter focal length.
An even wider angle was found: 21 mm!

02/26/2011 Casio TRYX camera. Focal length 21 mm EGF, matrix size 1/2.3", 12 MP, aperture - f2.8. Some shifted pointed out.

07/31/2011 Found 1 more compact with the same angle! Camera Samsung WB210. The focal length of the lens is 24-288 mm, but in special mode it produces 21 mm EGF. Matrix size 1 / 2.3", 14 MP, aperture - f2.9-f5.9 (and f3.4 in 21 mm mode). Andronov Andrey, Volgograd region pointed out the camera.

Aug 28, 2013 Found a compact with an even wider angle! Camera LUMIX DMC-FZ72. The focal length of the lens is 20-1200(!) mm, apparently the world's largest superzoom (60x). Matrix size 1/2.3", 16.1 Mp, aperture ratio - f2.8-f5.9, manual settings, weight: 606 g. Specified the camera as Victor, Kemerovo.

For 2013, the widest-angle focal length of the compacts
has LUMIX DMC-FZ72 - 20 mm in EGF!

So together we are looking for and find the widest angle!

5 years have passed, and a wider angle than 20 mm has not been found (perhaps this is the limit for compact cameras). However, I received a letter about another camera with EGF 20 mm.

04/04/2018 The focal length of the lens is 20 mm with a viewing angle of 94°. Camera FC330 as part of the DJI Phantom 4 quadrocopter. Matrix size 1/2.3", 12.4 MP, aperture - f2.8. Someone who wished to remain incognito pointed out the camera.

For 2018, the widest-angle focal length of 20 mm in EGF from compacts
have only 2 chambers mentioned above.

Have you ever wondered how the focal length of a lens affects the aesthetics of a photograph? Even when shooting the same scene, choosing a different lens can make a big difference in how the photo looks. The fact is that different focal lengths of the lens when shooting the same subject change the nature of the relationship between the subject and its background, and also affect the perception of the distance between them.

The illusion of reduced distance between the subject and the background is a property of telephoto lenses. They tend to flatten the image, while wide-angle lenses increase the effect of perspective. Do you know why 85mm lenses are so popular in portrait photography? These lenses have the effect of "flattening" the image plane, so that the nose and facial features do not appear larger in the picture than they really are.

While many people don't like using discrete lenses (fixed focal lengths), using this technique makes for great portraits. Personally, I shoot most portraits with 50mm or 85mm lenses. There are a number of reasons for this. First, such lenses flatten the image plane. With a telephoto lens, we can reduce or completely eliminate the geometric disproportions of facial features caused by the effect of perspective. The same applies to body parts of the subject.

The use of telephoto lenses also affects the depth of field. You may already know that depth of field is the range of distances from the camera where objects will be in sharp focus. Some people think that depth of field depends only on the aperture value of the lens, but the focal length of the lens has no less effect on it. A telephoto lens reduces the depth of field, helping to separate the subject from the background.

Often this is exactly what is required for portrait photography. By choosing a long lens, you take the background out of focus and draw the viewer's attention to the subject. And vice versa - the use of wide-angle lenses allows you to sharply convey not only the subject, but also its surroundings.

However, there is no perfect lens or focal length that fits all occasions. If you want to show how your subject relates to your surroundings, experiment with different focal lengths to see how they affect the relationship between subject and background.

To illustrate, I took a series of shots on the bridge near my house. Notice how the relationship between the bridge and the model changes in these shots.

I have used different focal lengths. The first lens was the Tokina 12-24mm f/4. The second is Nikon 35mm f/1.8. The last one is Nikon 80-200mm f/2.8 set to 100mm and 200mm. All shots were taken at f/2.8 to equalize the effect of depth of field (with the exception of Tokina set to f/4).

(Keep in mind that the pictures were taken on a Nikon D300 camera, so the focal length modifier must be taken into account since this is a DX format camera)

So let's take a look at the pictures. In each of them, I tried to keep the same composition, and the model occupied almost a full frame in height. Please note that the model takes up approximately the same space in the pictures, but the background is significantly different. Most striking is the difference in the size of the bridge in the background.

The first shot was taken at the widest angle (12mm focal length) with a Tokina 12-24mm lens. You can notice a strong perspective effect. The lines of the road lead the eye towards the bridge, which is barely visible in this picture. A wide angle also leads to a large depth of field - almost everything in the picture is in focus. As a result, everything is included in a single scene.

This shot was taken with a Nikon 35mm f/1.8 lens. 35mm is in the middle of the usual focal length range. The bridge now appears closer to us and the depth of field is shallower compared to shots taken at 12mm. Although the angle is still quite wide, and we have just begun to separate the object from the background.

Here we are in the region of ideal focal lengths for portraiture. The picture was taken with a Nikon 80-200mm f/2.8 lens set to 100mm. Note that the model image has become more "flat". The bridge now appears much closer to the model, and we've removed the effect of the road lines leading the viewer's eye away. In addition, we began to get rid of the large depth of field by isolating the subject from the background. This focal length is well suited for shooting faces and waist-length portraits.

In the last shot, the lens was set to 200mm. The distance compression effect has reached its maximum, and the model appears to be standing very close to the bridge. We also got a very shallow depth of field, almost completely separating the model from the background. Even though we were shooting the same person standing in the same spot, the different focal lengths resulted in completely different shots.

Conclusion

In this tutorial, I tried to show you the benefits of using different focal lengths. Test shots show that changing the focal length changes the scene.

Experimenting with focal length is a powerful creative tool. Choosing the right focal length is very important for getting the right composition for your shot. Wide-angle lenses allow you to include the background or create depth in your shot. Long lenses compress the distance between the subject and the background. In general, for each scene, you need to select the appropriate focal length of the lens.

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Translated from the site photo.tutsplus.com, the author of the translation is indicated at the beginning of the lesson.