Crop factor and equivalent focal length

Read also:

  • Lenses, part I. What is more important – a camera or a lens? Getting to know optics
  • Lenses, part II. Characteristics and properties of lenses
  • What are the lenses? Why take a portrait, and what a landscape?

How does the size of the camera matrix affect the viewing angle of the lens?

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

The smaller the focal length of the lens, the wider its viewing angle.

The larger the focal length of the lens, the narrower its viewing angle.

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: it “brings closer” the scene being shot stronger or weaker. Will these ratios between the focal length and the viewing angle be preserved or changed in case of a camera change? Today we will find out. Often when discussing pictures, photographers say: “this picture was taken with such a focal length”, thereby characterizing the viewing angle at which the picture was taken. Even under photo examples, our articles often indicate the focal length of the lens to which these images were shot. How do you know which focal length on your camera corresponds to the same viewing angle? How to take the same photo on your camera?

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

History tour

Previously, in the film era, 35 mm format film was the most widespread – an ordinary film film familiar to every person. It was used everywhere, starting from the simplest compact cameras (perhaps everyone had a film “soap box”), ending with serious professional equipment. Since all devices had the same area of ​​the photosensitive element (film frame), on all devices lenses with the same focal length gave the same viewing angle. For example, on any camera working with a 35 mm film, a lens with a focal length of 50 mm had a viewing angle of 45 °. Recall that in modern full-frame digital cameras, a sensor is used that is equal in size to the film frame – 24×36 mm.

Lens viewing angle and sensor size

Today the situation has changed. The matrices in digital cameras come in different sizes.

Modern camera sensor formats

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. Take a look at the diagram:

The smaller the camera’s matrix, the narrower the viewing angle of the lens at the same focal length

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 ”format matrix, the same lens will give a viewing angle of only 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 a completely different picture. This must be considered when choosing optics.

Crop factor and equivalent focal length

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

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

Equivalent Focal Length (EGF)

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

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

How to calculate the equivalent focal length for yourself? To do this, you need to know the crop factor . This is a conditional factor reflecting a change in the viewing angle of the lens when used with smaller matrices. This factor is derived by comparing the diagonals of the matrices of digital devices with a film frame of 24×36 mm. The word “crop factor” comes from the English words crop – “crop” and factor – “multiplier”.

For example, the diagonal of the APS-C format matrix is ​​approximately 1.5 times smaller than the 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 ​​2.7 times smaller than the full-frame one. 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. Suppose we need to know the equivalent focal length for a 35 mm lens if it is mounted on a camera with an APS-C sensor. 35×1.5 = 50mm. So, the equivalent focal length of such a lens will be 50 mm. That is, on an amateur DSLR, a 35-mm lens will behave the same as the classic “fifty dollars” in full frame.

Photo taken with a full-frame camera and a lens with a focal length of 20 mm. What happens if you install the same lens on a camera with an APS-C sensor or on a Nikon-1 device? The viewing angle will become narrower. Only the areas shown in the image will be included in the frame.

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

Matrix sizes and crop factor of Nikon photographic equipment

In Nikon’s current system SLR and mirrorless cameras, only three matrix standards of various sizes are used. They are easy to understand.

Full-frame matrices (Nikon FX). They have a physical size of 36×24 mm, that is, they are equal in size to a frame from a 35 mm film. Most modern lenses are designed for such cameras. And on them they can reveal their full potential. Among modern Nikon devices, the 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 the film frame, the concept of crop factor and EGF is not necessary for such devices.

APS-C format matrices(Nikon DX). They have a physical size of 25.1 x 16.7 mm and a crop factor of 1.5. Such a matrix is ​​slightly smaller than full-frame, but much cheaper. Such matrices are sometimes called “cropped” (trimmed). Almost all manufacturers of digital SLR cameras use this matrix size. Among modern Nikon devices, APS-C matrices have Nikon D3300, Nikon D5300, Nikon D5500, Nikon D7100 cameras. You can still use full-frame optics with them, however, all lenses will be much closer to “zoom in”, which is not always convenient, because some lenses are designed for a strictly defined type of shooting and their loss of the desired viewing angle does not allow them to be used for their intended purpose. First of all, it concerns wide-angle, portrait and reportage optics. Full-frame wide-angle optics lose their main advantage – a large viewing angle; full-frame portrait lenses on the crop begin to be brought too close, and it becomes difficult to shoot with them; you have to go very far. For example, installing a classic portrait lens with a focal length of 85 mm on a cropped camera, you will have to move 5-7 meters away from the person being photographed to take at least a portrait by waist. Full-frame reporting optics (primarily zoom lenses with a focal length of 24-70 mm) receive uncomfortable viewing angles on the crop, which are not very suitable in practice for fast, dynamic reporting. having installed a classic portrait lens with a focal length of 85 mm on a cropped camera, you will have to move 5-7 meters from the person being photographed to take at least a portrait waist-high. Full-frame reporting optics (primarily zoom lenses with a focal length of 24-70 mm) receive uncomfortable viewing angles on the crop, which are not very suitable in practice for fast, dynamic reporting. having installed a classic portrait lens with a focal length of 85 mm on a cropped camera, you will have to move 5-7 meters from the person being photographed to take at least a portrait waist-high. Full-frame reporting optics (primarily zoom lenses with a focal length of 24-70 mm) receive uncomfortable viewing angles on the crop, which are not very suitable in practice for fast, dynamic reporting.

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

It is important to keep in mind that on DX-lenses (designed for cameras with an APS-C sensor), the real, not equivalent focal length is indicated

For the same reason, they will not be able to work correctly on full-frame mattresses. What happens if you install a “cropped” lens on a full-frame camera? Unlike Canon cameras, Nikon has this capability. In this case, a very strong darkening at the edges of the frame will be obtained. By the way, modern full-frame Nikon devices 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.

The photo was taken on a full-frame camera with a lens with a focal length of 85mm.

NIKON D810 / 85.0 mm f / 1.4 Installations: ISO 80, F1.4, 1/1250 s, 85.0 mm equiv.

The photo was taken on a camera with an APS-C sensor with the same lens and from the same distance. As you can see, the lens on the crop gave a narrower viewing angle.

NIKON D5300 / 85.0 mm f / 1.4 Installations: ISO 100, F1.4, 1/1600 s

Photos are taken with the same lens from the same distance. As you can see, the option made for the “cropped” camera has a narrower viewing angle, less detail has entered the frame.

Nikon CX is a matrix format for mirrorless Nikon 1 family. Physical size – 13.2×8.8 mm. They have a crop factor of 2.7. Such a small matrix provides the entire system with compactness. It develops its own optics: it is compact and practical. Through a special adapter (Nikon FT-1) on Nikon 1 cameras, you can also use lenses for full-frame and APS-C devices.

Through the Nikon FT-1 adapter, you can mount lenses from DSLRs on cameras of the Nikon 1 family.

Other manufacturers have matrices of other sizes, and therefore with a different crop factor. For example, the micro 4/3 matrix standard, widely used by several manufacturers at once, is widely known. This standard has a crop factor of 2. These are not very large matrices, with all the ensuing pros and cons. Cameras equipped with such arrays are compact, as well as the optics developed for them. However, it is very difficult for devices with such a sensor to compete in the quality of the image with full-frame devices – the matrix area differs four times.

Summary

If you are going to buy a new camera or choose a new one to the old one and want to perform an approximate calculation of the viewing angle of the lens, find out the crop factor of the matrix installed in it. Based on this, choose the technique. If your camera has a crop factor of 1.5, be aware that you will need shorter-focus optics than for full-frame cameras. In the next lesson, we’ll talk about which lenses with which focal length are suitable for certain types of shooting, which lens is suitable for shooting portraits , and which lens is suitable for shooting landscapes .


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