The camera shutter is a special mechanism that is needed to transmit light to the camera matrix for the required period of time (shutter speed).
Gate designs are numerous and varied. The most common is a curtain shutter, consisting of two fabric or metal curtains, which at the time of shooting form between them a slit of different widths (depending on the shutter speed), which “runs” along the frame, allowing the required amount of light to enter the matrix.
Shutter speed is the time during which the camera's sensor is exposed to light passing through the lens.
Example of a camera shutter
Shutter speed is indicated in seconds, and they are indicated by a number with a double prime ("") instead of a decimal point, symbolizing the second (2""5, 0""8), or, much more often, in fractions of a second, and only the denominator is indicated, and the numerator is taken equal to 1, that is, a shutter speed of 60 means a time of 1/60 of a second. The symbol “B” (from English word“Bulb”) means that the camera’s sensor will be open to light for an unlimited time. When the photographer presses the shutter button, the shutter opens. When the button is pressed a second time, the shutter closes. Using this function, you can get a shutter speed of several hours, which can be useful when photographing the starry sky.
Electronic shutter
In the first film cameras, the shutter was a mechanical device. In modern digital cameras, the shutter is designed as an electronic circuit that controls the process of reading information from the matrix. For ease of understanding, an electronic shutter can be represented as a special electronic circuit that supplies voltage to the matrix for a certain time (dwell time), while the rest of the time the matrix is de-energized.
An electronically controlled mechanical shutter is often called electronic.
Depending on the method of reading information from the matrix, there are two types of electronic shutters: global shutter (global shutter, the image is completely formed) and rolling shutter (rolling shutter, line-by-line reading technology).
With a frame shutter, a digital image is formed instantly, just like when photographing, i.e. all pixels of the matrix allocated for operation transmit information simultaneously. The operating time of the sensor is equal to the shutter speed, which is set in the camera in advance.
With a rolling shutter, a digital image is created not by instantly reading information from the matrix, but by sequentially scanning it. Those. information from the sensor is not transmitted all at once, but line by line - from top to bottom, while the shutter seems to slide across the frame. Again, the concept of a shutter here is arbitrary and has nothing to do with mechanical implementation.
The operation of electronic shutters can be shown in a simplified manner in the following pictures:
Using an electronic shutter allows you to achieve fast shutter speeds without using expensive high-speed mechanical shutters.
Basics of Photography #5.8
In several previous articles I covered two type 1 designs of photographic shutters: curtain-slot and leaf. Both types are so different from each other that each of them has a diverse set of features that it is advisable for the photographer to take into account in his practice.
Despite significant differences, both curtain-slot and leaf shutters are external devices in relation to the photosensitive sensor and refer to mechanisms. In other words, the devices considered have dimensions commensurate with the dimensions of the sensor, include moving components and perform their function - blocking and “dosed” transmission of the flow of light rays - thanks to the movement of parts.
An electronic shutter (from the English electronic shutter) - I will address it in this and several subsequent articles - hardly has at least one of the listed properties. Here a new universe opens up with individual patterns and resulting features that it is advisable for a photographer using digital technologies to pay attention to if he wants to achieve high-quality results at optimal costs. I propose to smoothly move into the universe of the Electronic Shutter and figure out how “everything” works in it, and how its structure affects the creation of photographic images. I will say right away that this universe is not only interesting and promising, but already in the present tense it reveals to photographers of various directions possibilities that a few years earlier (about 5-25 years ago) existed only in the imagination. For example, capturing the collision of a rocket with an obstacle in natural light shooting conditions without an electronic shutter is hardly possible.
To make further presentation as effective as possible for you, I suggest you pause and remember the design and operating principle of the photosensitive sensor, as well as the types of sensors used in photography. Brush up on your knowledge with Part 2 of Part 4 of the Photography Basics series.
What is an electronic shutter?
I will approach the search for an answer from the other side. First, I will describe what the electronic shutter does not have, and what the latter is not.
It barely has any moving mechanical parts. Moreover, the electronic shutter is hardly a mechanism. I cannot touch it, see it, describe its component parts, their location relative to each other.
The electronic shutter, in fact, does not “shutter” the light, does not block the path of light rays on a par with its “big brothers”. In other words, the word “shutter” in the name is rather nominal. However, the electronic “shutter” successfully performs the same basic function that both the curtain-slot and leaf shutters perform. Let me formulate it as follows.
The main function of any photographic shutter is to provide the photographer with the ability to control the light that continuously irradiates the photosensitive layer over time. The diaphragm can change the illumination of the latter, in other words, regulate the number of light rays that reach the surface of the photosensitive layer. The shutter can interrupt the radiation. It makes it possible to make the continuous flow of light rays that reach the surface of the photosensitive layer finite in time.
Apart from the fact that an electronic shutter is not a mechanism, it is also not a device, a substance made up of atoms, or electromagnetic field, or even the interstellar medium.
Electronic shutter I will name the method by which the light-sensitive sensor takes into account the amount photons 2 that reached the surface of the latter.
The method is implemented simultaneously at several levels. At the level of atoms of physical substances (hence the name “electronic”, that is, “associated with electrons 3"), at the level of components that form the photosensitive sensor, and at the level of programs that control the physical processes occurring in sensor 4 .
The method is implemented in various ways, which, in particular, depend on the type of photosensitive sensor. The choice of method has a direct impact on the digital image created, as well as on both the technical and artistic capabilities of the photographer. Starting with the next article, I'll look at six ways, essentially six light sensor designs, that you may encounter when photographing digitally. cameras 5. To increase the efficiency of consideration and facilitate the perception of methods, I will carry out preliminary preparation.
I will describe several structural features, characteristic features of an electronic shutter.
Design engineers of modern photographic systems can implement it, by definition, in digital cameras. However, you are unlikely to find an electronic shutter in film cameras. In the latter, the image is obtained due to a weakly controlled chemical reaction, rather than controlled sequential operations with electrons performed microcircuits 6. Therefore, the electronic shutter naturally appeared along with CMOS sensors 7 and photosensitive sensors built on the principle CCD 8 (from now on I will simply call such sensors CCD). Thanks to both, modern photography exists, in particular.
An electronic shutter, unlike a curtain-slot or leaf shutter, which are separate and removable mechanisms, can hardly be located anywhere other than “inside” the light sensor. The electronic shutter can be considered as one of the sensor functions. If necessary, service center Your curtain-slot or leaf shutter may be replaced, and instead of replacing the electronic shutter, a qualified specialist will suggest that you replace the light sensor and/or, possibly, the control circuit of the camera and/or built into the latter software, the so-called “firmware” (in English firmware).
I gave a definition and designated “external” characteristic features electronic shutter. Now let me turn to the practical side.
Both a regular film camera and a modern digital camera have optical system lenses, aperture and shutter. We can say that from the point of view of the basic operating scheme of a photographic device, little has changed with the advent of digital photographic equipment: light rays are collected in the lens and then directed through an opening (diaphragm) to a light-sensitive element (sensor). In this scheme, the shutter and aperture are elements invisible to the photographer's eye, which, nevertheless, have a huge impact on the result of the shooting. Why were these elements, well known from film cameras, retained in modern digital photographic equipment? What are they for? How do the aperture and shutter work in a digital camera?
Digital cameras use several different types of mechanical shutters, but they all serve the same purpose. They block light from reaching the sensor when closed and move out of the way to allow light to accumulate on the sensor when it is open. Why is a shutter needed? Understanding that some cameras have all-electronic shutters while others have mechanical shutters, it's clear that there are pros and cons for both designs. The cameras, typically smaller spot cameras that do not use mechanical shutters, typically use an intermediate gear sensor.
The purpose of the shutter and aperture
Gate- this is one of the main mechanisms of a digital camera, which is responsible for transmitting light rays to the photosensitive element (matrix) for a given period of time when the photographer presses the shutter button. The main purpose of the shutter is to regulate the duration of passage luminous flux through the camera's optical system.
The interline sensor allocates a portion of each pixel to store charge for that pixel. The added electronics required to store charge for each pixel reduce the pixel's fill factor, in turn reducing its ability to capture light since a portion of each pixel is not sensitive to light. Microlenses can be used to compensate, but they are not 100% effective and they can add design costs. One obvious advantage is that this design eliminates the need for a potentially bulky mechanical shutter and can turn a wallet-sized camera into a pocket-sized shirt camera.
The time for which the camera shutter opens is called shutter speed or exposure time. If the shutter speed is less than a second, then it is indicated as the denominator of the fraction, indicating a fraction of a second. For example, 1/125 second or 1/30 second. Shutters installed in digital cameras are capable of closing and opening at high speed, thereby regulating the time the matrix is illuminated, that is, shutter speed, with high accuracy.
Digital cameras that use a mechanical shutter typically use a type of sensor called a full-frame sensor. Unlike the intermediate gear sensor, the sensor full frame has no circuitry on the pixel to store the charge that builds up when light contacts the array. Cameras that use a mechanical shutter typically discard any residual electrical charge when the shutter is closed, open the shutter, and close the shutter. Once the mechanical shutter is closed, circuitry is then used to shift charge from each pixel to the storage area.
The longer the shutter speed, the more light will hit the photosensitive element of the camera. From a photographer's point of view, the camera shutter must have high accuracy, reliability in various shooting conditions, and a wide range of shutter speeds. In modern digital cameras, the shutter is used not only to control shutter speed, but also to protect the sensor from light exposure while the image is being read or before exposure begins.
Mechanical blinds: bottom line
Because the pixels on the sensor remain "live" during readout, if the shutter remains open, light will continue to alter the charge stored by each pixel during the switching operation, which can result in blur or ghosting. In layman's terms, a mechanical shutter is used to control how long the pixels on the image sensor collect light. By using a mechanical shutter, a simpler, cheaper and more efficient sensor can be used: one that has a higher fill level. Of course, nothing is ever cut or dried out.
Diaphragm is a round, variable hole that is located inside the camera lens. The photographer can vary the diameter of the hole, thereby adjusting the flow of light entering the digital camera’s sensor. The size of this hole is determined by the f-number: the larger the aperture hole (small f-number), the more light falls on the matrix and vice versa.
Some cameras use both a mechanical and electronic shutter! This article aims to answer the question of why a digital camera, admittedly a "solid state" device that shouldn't logically need any moving parts other than a focusing mechanism, needs a mechanical shutter.
Basics of Photography #5.8
It won't cost you anything extra. In this video and article we'll cover what shutter speeds and shutter angles are, how shutter speed or shutter angle can be used to control motion and exposure, and what settings to use to get a "movie" look.
In digital cameras, the aperture number can be changed within a fairly wide range, for example, for the Tamron AF 18-270mm f/3.5-6.3 Di II VC lens, from f/3.5 to f/6.3. In addition, the aperture also affects the depth of field of the imaged space, allowing the photographer to control the creative process. As is already clear, shutter speed and aperture are interdependent parameters. Together they make up the so-called expo couple: Decreasing one of these parameters increases the other.
A camera shutter is a device that allows light to pass through for a short period of time. While the aperture controls the area through which light can pass, the shutter controls the period of time through which light can pass. This means that the longer the shutter is left open, the more light passes through.
Understanding Shutter Speed
A fast shutter speed means that the shutter opens and closes quickly, allowing only a small amount of light to pass through. A slow shutter speed means the shutter stays open longer, allowing more light to pass through. Traditionally, camera shutter speeds are expressed in seconds at fixed intervals. The difference between shutter speed and amount of light is linear; which means double the speed, double the light - or half the speed, half the light.
Photographic shutter: operating principle and types
At the moment when a photograph is taken, the camera shutter opens. Light rays pass through the lens, hit the diaphragm, which controls the amount of light, and ultimately reach the photosensitive element. After light hits the digital camera sensor directly, exposure of the frame begins. Then the shutter closes. In a moment, the camera will be ready to shoot the next frame. By opening and closing, the shutter, like the diaphragm, ensures a change in the amount of light falling on the matrix.
Here are the standard shutter speeds you'll find on most professional cameras. These aren't the only shutter speeds. Professional cameras allow you many values between them, for greater illumination. The only thing you have to remember is that every time you double or halve your shutter speed, you do the same to the amount of light it lets in.
There are many ways you can block light coming through your window, and shutter technology is no different. The most popular types of shutters are. When it comes to video, you only have to worry about electronic shutters and spinning platters. Electronic blinds follow the shutter system described above. Spinning discs have their own version.
Naturally, no matter how perfect the photographic shutter is, it requires, albeit short, a certain period of time to open. It also takes some time to close it. In this regard, three stages or phases can be distinguished in the operation of a photographic shutter.
The first phase is associated with opening the active lens aperture. The next one is the phase of complete opening of the existing hole. And finally, the last phase is the closing phase, that is, a certain period of time from the beginning of the reduction of the existing hole until its complete closure. From this we can understand that during this entire shutter cycle, the effective lens aperture remains fully open only a certain part of the time.
The simplest type of rotating disc gate is the semi-circular one, as shown above. It only has one shutter speed setting. Obviously you need some method of controlling the length of time. For this reason, rotating disks in video cameras can adjust the shape of the shutter, for example.
Photographic shutter: operating principle and types
Instead of shutter speeds in seconds, rotating butterfly valves use shutter angles. The wider the shutter angle, the more light passes through. The ratio is designed to be similar to shutter speed - halving or doubling the angle will reduce or double the light.
In this regard, one of the most important characteristics shutter is optical efficiency(efficiency), which determines the ratio of the amount of light passed during the operation of the shutter to the amount of light that could pass through an “ideal” shutter in the same period of time. The more the efficiency value approaches unity (that is, 100%), the more perfect the shutter operates. In other words, the less time during a given shutter speed it takes to open and close the shutter, the longer the lens aperture will be fully open, which means more light will pass through the lens. In this regard, we can say that a good photographic shutter can more fully reveal the aperture of the lens.
High frame rate
This corresponds to half the time each frame will take one second. Want a simple formula to find out the relationship between shutter angle, shutter speed, and frame rate? Why does high frame rate shooting require so much more light?
Now imagine shooting at 1 million frames per second. Only the sun can illuminate something like this on a budget. Should you stick to the "formula"? Factors influencing the choice of shutter speeds. Electrical Frequency Exposure Frame Rate Limitations of Electronic Camera Shutter Motion Blur. Once you can learn how to control your shutter speed, you'll be well on your way to cinematography mastery.
All digital camera shutters have special controls that allow you to set the shutter speed required for a given photograph. However, the appropriate shutter speed can be determined automatically by the camera. Many cameras provide a special mode for completely manual control of the shutter opening time (Bulb), through which the shutter can not only open, but also close strictly at the photographer’s command. This mode is very relevant when shooting at long exposures when the camera is mounted on a tripod.
Exclusive Bonus: Download my free blacksmith of the most important and useful focal lengths for film and video. The latter in particular hints at a future where cameras no longer require mechanical curtains. But what is an electronic shutter? Well, let's rewind a little.
Ethics Statement: We were not asked to write anything about these cameras and did not provide any compensation. There are affiliate links inside the article. Don't worry - prices remain the same for you. To learn more about our ethics, you can visit our.
According to their design and operating principle, shutters in digital cameras are divided into the following types:
- Electronic shutter
If in film cameras a mechanical shutter was installed, which opened and closed the curtains, limiting the exposure of light to the film, then in digital cameras its role is played by an electronic shutter. Almost all digital cameras are equipped with just such an electronic equivalent of a shutter, which is built directly into the camera sensor.
Mechanical vs electronic shutter
By default, when shooting with a mirrorless camera, there are two mechanical curtains that open and close in front of the digital sensor, exposing the pixels for the period you select. Below you can see a time-lapse video of the two cameras' mechanical shutters in action.
The electronic shutter simulates this movement by turning on the pixels on the digital sensor for the required amount of time. There are various types Electronic shutters: The global shutter used in high-end digital cameras can activate all pixels at the same time. Put different words, imagine a scanner analyzing a photograph: the sensor moves from one side to the other to capture the image. The electronic shutter works in a similar way, as it "scans" the light passing through the lens.
It is a kind of switch that turns on the sensor to receive the light flux at the right moment and turns it off at the command of the processor. The electronics and processor of the camera completely control the operation of such a shutter. The peculiarity of the electronic shutter is that light constantly enters the matrix, which allows, in particular, to transfer the image from the matrix to the camera’s LCD display. When the electronic shutter is triggered, the image from the camera matrix is read within a certain period of time. This interval between zeroing the matrix and the moment of reading electronic information from it constitutes the holding time in this case.
The electronic shutter scans the light entering the sensor. The electronic shutter has been around for many years. At first, it mainly proved useful to avoid vibrations caused by mechanical curtains and for silent shooting. I've had the opportunity to work with some of these cameras on contemporary dance shows where scenes where there was no music were common and, as you can imagine, silence was mandatory.
Then we started to see other improvements, such as the ability to go beyond the maximum shutter speed of the mechanical shutter.
However, the electronic shutter also introduced some limitations. Some of them are minor and vary from model to model.
The advantage of using electronic shutters in modern digital photography is that with their help it is possible to achieve very fast shutter speeds. Such a shutter, in particular, is capable of operating shutter speeds up to 1/8000 or 1/15000 s. In addition, the electronic shutter is silent and vibration-free.
However, it also has its drawbacks. This is, first of all, low quality associated with various image distortions, which are caused by sequential reading of matrix cells. Due to constant exposure to light, the electronic shutter is prone to ghosting, blooming and other unpleasant effects. That is why in advanced compact cameras In professional digital devices, in addition to the electronic shutter, there is always a traditional mechanical shutter. Cheap digital camera models use only an electronic shutter.
On the latest models, many of these issues have either been fixed or improved. Then we have more important issues like distortion and binding. They are also common for video recording, as the camera also uses an electronic shutter for video.
Distortion occurs because the camera cannot "scan" the sensor fast enough when fast movements are involved.
Banding can occur using high-frequency artificial lighting. It creates different brightness intensities and color bands in your image. In some cases, another problem may be resolved, but not always.
Despite the advent of digital photographic equipment with electronic shutters controlled by powerful processors, the mechanical shutter is not a thing of the past. It's still used in decent digital cameras, only now it's paired with an electronic camera. The synchronized operation of these two shutters makes it possible to achieve fast shutter speeds and at the same time avoid the appearance of halo around contrasting images. In professional SLR cameras and advanced compacts, the electronic shutter is used only for ultra-short shutter speeds, while the mechanical shutter mainly works.
Olympus and the evolution of speed
Is the electronic shutter the future of DSLR cameras? Let's try to answer this question by analyzing these two cameras a little closer. The question arises: why choose an electronic shutter over a mechanical shutter? In this case, the answer is speed.
Speeds of up to 60 frames per second may seem excessive, but in certain situations they can be useful for capturing certain types of action, such as an arrow hitting a balloon in the example below. Some photographers have also emphasized its use for certain types of studio work, such as throwing colored dust or water onto a model. When you press the shutter button halfway, the camera begins to load images into its virtual memory, so that by the time you press the button all the way down and start shooting, up to 14 images can already be recorded on the memory card.
In addition to the fact that the mechanical shutter doses the light falling on the photosensitive element of the camera, it also serves to additionally protect the matrix from dust and dirt. After all, the matrix is the most expensive element of a digital camera, especially when it comes to a professional camera. The mechanical shutter itself has a certain service life and eventually fails.
According to their design, mechanical shutters are traditionally divided into two types - central and curtain (curtain-slit) shutters. The central shutter is usually installed between the objective lenses. It uses shutters in the form of thin petals that open the light opening of the lens from the optical axis to the edges and close in the opposite direction. This ensures an even distribution of illumination across the entire field of the frame. The highest efficiency is achieved by the central shutter whose light-protective shutters operate at the highest speed.
The central shutter has quite a lot of advantages: no image distortion as a result of operation, uniform light distribution and good resistance to temperature fluctuations. However, compared to curtain shutters, central shutters have a lower efficiency and a lower minimum speed, that is, a shorter instantaneous shutter speed.
As for the curtain or curtain-slit shutter, it uses a light-proof curtain consisting of two parts separated by a transverse slit. The light coming from the lens penetrates into this gap. When the shutter is released, the curtains move one after another: the first light curtain opens the frame window, and the other, accordingly, closes it. The shutter speed here depends on the width of the slit.
The main advantages of the curtain shutter are its high efficiency (can reach 95%) and the ability to handle short shutter speeds (up to 1/1250 s in some models). But when shooting fast-moving objects, using a curtain-slit shutter often leads to displacement and distortion of individual image elements. Curtain shutters are also characterized by the fact that they are more susceptible to temperature fluctuations.
- Electron-optical shutter
Along with the electronic shutter, some models of digital cameras use an electro-optical shutter rather than a mechanical one. This is a liquid crystal that is located between two parallel polarized plates. Through it, the light flux passes to the electron-optical converter of the camera. When a voltage is applied to the thin electrically conductive coating on the inner surface of the plates, an electric field arises that changes the plane of polarization of the liquid crystal by 90 degrees. As a result, maximum opacity of the crystal is ensured and, as a result, the liquid crystal shutter closes. In the absence of voltage, light enters the matrix through the liquid crystal. Since there are no mechanical elements, the electro-optical shutter is quite reliable and simple.
Digital camera aperture
The diaphragm in its classic form is designed as a light-proof shutter formed by thin metal petals moving towards the center of the lens. This is the so-called iris diaphragm. Thin blades, placed in a circle along the rim of the lens, rotate and thereby increase or decrease the opening through which light enters. The more open the aperture blades are, the more light passes to the photosensitive element. Aperture control in digital cameras can be carried out in manual or automatic modes.
Manual control The aperture is usually implemented in the form of a ring on the outer surface of the lens frame, on which the aperture number scale is marked. When the aperture ring rotates, the blades move. Moreover, each transition from one aperture value to an adjacent value ensures that the amount of light passing through the lens changes exactly twice. Aperture priority mode is very convenient, when you can set the aperture yourself, and the camera will set all other shooting parameters automatically. Controlling the aperture in automatic mode carried out through the electronics of the camera based on the analysis of specific photographic conditions.
Changing the aperture immediately affects two key properties of the image - aperture and depth of field. Aperture refers to the maximum amount of light that a given lens is capable of transmitting. In daylight conditions, adjusting and controlling the aperture of a digital camera is not particularly difficult. But in low-light conditions, such as when shooting in a dark room, the photographer has to shoot with a large aperture to prevent the photo from coming out dark. This requires flexible control of the aperture to compensate for the lack of light.
The size of the aperture also determines the area that will look sharp in the photograph. In other words, the aperture determines whether the background in the photo will be blurry or sharp. For example, a small aperture is used to blur the background and perspective. Depth of field extends from the center to the edge of the image, so the closer to the edge of the image, the blurrier the object will be. On the contrary, a large aperture is used in cases where everything in the photo needs to look sharp. In general, aperture control provides the photographer with complete freedom of action and a wide field for creative experiments.
Speaking about the shutter and aperture of a digital camera, it should be noted that in some modern cameras the aperture can be combined with a central leaf shutter. In this case, the aperture mechanism operates exactly at the moment the shutter is released, and at the same time the shutter blades diverge to a distance that corresponds to the set aperture value. But such combined shutter-diaphragms with regulation of the size and duration of opening of the light hole are installed mainly in entry-level cameras. Although they provide greater compactness of photographic equipment.
The problem is that, due to its design, the combined shutter-diaphragm mechanism is only capable of working with exposure pairs such as long shutter speed - minimum relative aperture or short shutter speed - maximum relative aperture. This linearity of exposure parameters results in the fact that, for example, in low light conditions, the camera will use long shutter speeds with an open aperture, which, naturally, will negatively affect the quality of the photographic image. In addition, aperture shutters are not capable of providing a wide range of shutter speeds and aperture values.
The shutter and aperture remain the main mechanisms of a photographic camera in the digital era. Along with the characteristics of the lens, the shutter and aperture largely determine the quality of the photographic image. Opportunity manual settings aperture and shutter speed provides the photographer with space for creative experiments and fine-tuning his digital camera for specific shooting conditions.
One of the main mechanisms of digital cameras is the shutter; its functional purpose is to let light rays through to the matrix, which is a photosensitive element, when you press the button. Light rays are passed through for a certain period of time. This period of time during which the shutter opens is called " excerpt" A special feature of digital devices is the installation of shutters that can close and open at very high speeds, thanks to which the exposure time (matrix illumination) is adjusted with high precision. It is very important for specialists that photographic equipment has such accuracy, as well as a large range. With a long shutter speed, more light enters the matrix. The shutter of modern digital cameras, especially for professional use, can effectively control shutter speed. At the same time, this element protects the matrix from flare, which can occur when reading an image at the very beginning of the exposure.
Types of valves
Gates may differ in their design, as well as in the principle of closure. Based on these features, these elements are divided into electronic and mechanical. Various models of digital photographic equipment have an electronic shutter that is built directly into the camera sensor.
Electronic shutter
At the right moment, it turns on the sensor to receive the light flux, and then turns it off at the command of the processor. The operation of such a shutter is controlled by the camera processor and its electronic equipment. When using this electronic element The light flux hits the matrix constantly, thanks to which the image from the matrix is transmitted to the LCD display of the digital device. Such an image is read in a certain time, which lasts between zeroing the matrix and the moment when the electronic information is read. This time is the shutter speed that characterizes the camera. Thanks to electronic shutters, the photographer can use fast shutter speeds, even up to 1/15000s. The electronic shutter operates without noise or vibration. The only thing is that when using such a shutter, you can observe low image quality, since the reading of the matrix cells occurs sequentially. In order to avoid image distortion and unpleasant effects such as halo and blooming, professional photographic equipment is also provided with a mechanical shutter.
Mechanical shutter
Provides additional protection of the matrix from fine dirt and dust. He also does this important function, as the dosage of light hitting the photosensitive element of the camera, that is, the matrix. Thanks to the mechanical shutter, the expensive matrix retains its high technical qualities. This type of shutter has a certain service life.
Mechanical valves are also divided into two groups - curtain and central.
Central shutter
It is a structure made of thin plates ( petals), opening towards the edges and closing in the opposite direction, so the light flux is distributed evenly. It is installed between the objective lenses. The valves in which the valves open very quickly are of greatest value to professionals.
Curtain shutters
Possess more high speed and greater instant endurance. The design of a curtain shutter uses two parts (curtains), which are separated from each other by a gap. The light flux from the lens penetrates into it. When the slit shutter is triggered, its first curtain opens the frame window, the second closes it. The shutter speed depends on the width of the gap that forms between the curtains. The principle of the curtain shutter, in which the curtains move, can lead to distortion of some objects in the photo. But this shutter handles short shutter speeds and has a high efficiency.
Electron-optical shutter
Digital cameras can also use an electro-optical shutter, which is a liquid crystal located between two polarized plates. A light flux flows through this crystal, then it hits an optical converter.
The shutter is important element operation of any photographic equipment. The basic operating principle of any type of shutter is to open during photography and allow light rays to pass through. When the light flux hits the photosensitive element, the frame is exposed. The next step is closing the shutter, which allows you to move on to the next shot. The shutter plays a very important role in the design of a camera. .
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Types of camera shutters
One of the main mechanisms of digital cameras is the shutter; its functional purpose is to let light rays through to the matrix, which is a photosensitive element, when you press the button. Light rays are passed through for a certain period of time. This period of time
One of the main mechanisms of digital cameras is the shutter; its functional purpose is to allow, when the button is pressed, light rays to the matrix, which is a photosensitive element. Light rays are passed through for a certain period of time. This period of time during which the shutter opens is called " excerpt" A special feature of digital devices is the installation of shutters that can close and open at very high speeds, thanks to which the exposure time (matrix illumination) is adjusted with high precision. It is very important for specialists that photographic equipment has such accuracy, as well as a large range. With a long shutter speed, more light enters the matrix. The shutter of modern digital cameras, especially for professional use, can effectively control shutter speed. At the same time, this element protects the matrix from flare, which can occur when reading an image at the very beginning of the exposure.
Types of valves
Gates may differ in their design, as well as in the principle of closure. Based on these features, these elements are divided into electronic and mechanical. Various models of digital photographic equipment have an electronic shutter that is built directly into the camera sensor.
Electronic shutter
At the right moment, it turns on the sensor to receive the light flux, and then turns it off at the command of the processor. The operation of such a shutter is controlled by the camera processor and its electronic equipment. When using such an electronic element, the light flux constantly enters the matrix, thanks to which the image from the matrix is transmitted to the LCD display of a digital device. Such an image is read in a certain time, which lasts between zeroing the matrix and the moment when the electronic information is read. This time is the shutter speed that characterizes the camera. Thanks to electronic shutters, the photographer can use fast shutter speeds, even up to 1/15000s. The electronic shutter operates without noise or vibration. The only thing is that when using such a shutter, you can observe low image quality, since the reading of the matrix cells occurs sequentially. In order to avoid image distortion and unpleasant effects such as halo and blooming, professional photographic equipment is also provided with a mechanical shutter.
Mechanical shutter
Provides additional protection of the matrix from fine dirt and dust. It also performs such an important function as dosing light onto the photosensitive element of the camera, that is, onto the matrix. Thanks to the mechanical shutter, the expensive matrix retains its high technical qualities. This type of shutter has a certain service life.
Mechanical shutters are also divided into two groups - curtain and central.
Central shutter
It is a structure made of thin plates ( petals), opening towards the edges and closing in the opposite direction, so the light flux is distributed evenly. It is installed between the objective lenses. The valves in which the valves open very quickly are of greatest value to professionals.
Curtain shutters
They have higher speed and greater instantaneous endurance. The design of a curtain shutter uses two parts (curtains), which are separated from each other by a gap. The light flux from the lens penetrates into it. When the slit shutter is triggered, its first curtain opens the frame window, the second closes it. The shutter speed depends on the width of the gap that forms between the curtains. The principle of the curtain shutter, in which the curtains move, can lead to distortion of some objects in the photo. But this shutter handles short shutter speeds and has a high efficiency.
Electron-optical shutter
Digital cameras can also use an electro-optical shutter, which is a liquid crystal located between two polarized plates. A light flux flows through this crystal, then it hits an optical converter.
The shutter is an important element in the operation of any photographic equipment. The basic operating principle of any type of shutter is to open during photography and allow light rays to pass through. When the light flux hits the photosensitive element, the frame is exposed. The next step is closing the shutter, which allows you to move on to the next shot. The shutter plays a very important role in the design of a camera.
Vendors now offer a huge selection of video surveillance cameras. Models differ not only in parameters common to all cameras - focal length, viewing angle, light sensitivity, etc. - but also in various proprietary features that each manufacturer strives to equip their devices with.
Therefore, often brief description characteristics of a video surveillance camera is a frightening list of incomprehensible terms, for example: 1/2.8" 2.4MP CMOS, 25/30fps, OSD Menu, DWDR, ICR, AWB, AGC, BLC, 3DNR, Smart IR, IP67, 0.05 Lux and that's not all.
In the previous article, we focused on video standards and the classification of cameras depending on them. Today we will look at the main characteristics of video surveillance cameras and decoding the symbols of special technologies used to improve the quality of the video signal:
- Focal length and viewing angle
- Aperture (F number) or lens aperture
- Adjusting the iris (auto iris)
- Electronic shutter (AES, shutter speed, shutter speed)
- Sensitivity (light sensitivity, minimum illumination)
- Protection classes IK (Vandal-proof, anti-vandal) and IP (from moisture and dust)
Matrix type (CCD CCD, CMOS CMOS)
There are 2 types of CCTV camera matrices: CCD (in Russian - CCD) and CMOS (in Russian - CMOS). They differ both in design and principle of operation.
| CCD | CMOS |
| Sequential reading from all matrix cells | Random reading from matrix cells, which reduces the risk of smearing - the appearance of vertical smearing of point light sources (lamps, lanterns) |
| Low noise level | High noise level due to so-called tempo currents |
| High dynamic sensitivity (more suitable for shooting moving objects) | “Rolling shutter” effect - when shooting fast moving objects, horizontal stripes and image distortion may occur |
| The crystal is used only to accommodate photosensitive elements; the remaining microcircuits must be placed separately, which increases the size and cost of the camera | All chips can be located on a single chip, making production of CMOS cameras simple and inexpensive |
| By using the matrix area only for photosensitive elements, the efficiency of its use increases - it approaches 100% | Low power consumption (almost 100 times less than CCD matrices) |
| Expensive and complex production | Performance |
For a long time it was believed that the CCD matrix produces much higher quality images than CMOS. However, modern CMOS matrices are often practically in no way inferior to CCDs, especially if the requirements for the video surveillance system are not too high.
Matrix size
Indicates the diagonal size of the matrix in inches and is written as a fraction: 1/3", 1/2", 1/4", etc.
It is generally believed that the larger the matrix size, the better: less noise, clearer picture, larger viewing angle. However, in fact, the best image quality is provided not by the size of the matrix, but by the size of its individual cell or pixel - the larger it is, the better. Therefore, when choosing a video surveillance camera, you need to consider the matrix size along with the number of pixels.
If matrices with sizes 1/3" and 1/4" have the same number of pixels, then in this case a 1/3" matrix will naturally give a better image. But if it has more pixels, then you need to pick up a calculator and calculate the approximate pixel size.
For example, from the matrix cell size calculations below, you can see that in many cases the pixel size on a 1/4" matrix turns out to be larger than on a 1/3" matrix, which means a video image with 1/4", although it is smaller in size, it will be better.
| Matrix size | Number of pixels (millions) | Cell size (µm) |
| 1/6 | 0.8 | 2,30 |
| 1/3 | 3,1 | 2,35 |
| 1/3,4 | 2,2 | 2,30 |
| 1/3,6 | 2,1 | 2,40 |
| 1/3,4 | 2,23 | 2,45 |
| 1/4 | 1,55 | 2,50 |
| 1 / 4,7 | 1,07 | 2,50 |
| 1/4 | 1,33 | 2,70 |
| 1/4 | 1,2 | 2,80 |
| 1/6 | 0,54 | 2,84 |
| 1 / 3,6 | 1,33 | 3,00 |
| 1/3,8 | 1,02 | 3,30 |
| 1/4 | 0,8 | 3,50 |
| 1/4 | 0,45 | 4,60 |
Focal length and viewing angle
These parameters are of great importance when choosing a video surveillance camera, and they are closely related to each other. In fact, the focal length of a lens (often denoted f) is the distance between the lens and the sensor.
In practice, the focal length determines the camera's viewing angle and range:
- the shorter the focal length, the wider the viewing angle and the less detail can be seen on objects located in the distance;
- The longer the focal length, the narrower the viewing angle of the video camera and the more detailed the image of distant objects.
If you need a general overview of an area and want to use as many fewer cameras- buy a camera with a short focal length and, accordingly, a wide viewing angle.
But in those areas where detailed observation of a relatively small area is required, it is better to install a camera with an increased focal length, pointing it at the object of observation. This is often used at the checkout counters of supermarkets and banks, where you need to see the denomination of banknotes and other payment details, as well as at the entrance to parking lots and other areas where it is necessary to distinguish a license plate number over a long distance.
The most common focal length is 3.6 mm. It roughly corresponds to the viewing angle of the human eye. Cameras with this focal length are used for video surveillance in small spaces.
The table below provides information and relationships focal length, viewing angle, recognition distance, etc. for the most common focuses. The numbers are approximate, as they depend not only on the focal length, but also on other parameters of the camera optics.
Depending on the width of the viewing angle, video surveillance cameras are usually divided into:
- conventional (viewing angle 30°-70°);
- wide-angle (viewing angle from approximately 70°);
- long-focus (viewing angle less than 30°).
The letter F, only usually capitalized, also denotes the lens aperture - therefore, when reading the characteristics, pay attention to the context in which the parameter is used.
Lens type
Fixed (monofocal) lens- the simplest and most inexpensive. The focal length is fixed and cannot be changed.
IN varifocal (variofocal) lenses you can change the focal length. Its setting is done manually, usually once when the camera is installed at the shooting location, and then as needed.
Transfactor or zoom lenses They also provide the ability to change the focal length, but remotely, at any time. The focal length is changed using an electric drive, which is why they are also called motorized lenses.
"Fisheye" (fisheye, fisheye) or panoramic lens allows you to install just one camera and achieve a 360° view.
Of course, the resulting image has a “bubble” effect - straight lines are curved, but in most cases, cameras with such lenses allow you to divide one general panoramic image into several separate ones, with adjustments for the perception familiar to the human eye.
Pinhole lenses allow for covert video surveillance due to its miniature size. In fact, a pinhole camera does not have a lens, but only a miniature hole instead. In Ukraine, the use of covert video surveillance is seriously limited, as is the sale of devices for it.
These are the most common lens types. But if we go deeper, lenses are also divided according to other parameters:
Aperture (F number) or lens aperture
Determines the camera's ability to capture high-quality images in low-light conditions. The higher the F number, the less open the aperture and the more light the camera needs. The smaller the aperture, the wider the aperture is, and the camcorder can produce clear images even in low light.
The letter f (usually lowercase) also denotes the focal length, so when reading the characteristics, pay attention to the context in which the parameter is used. For example, in the picture above, the aperture is indicated by a small f.
Lens mount
There are 3 types of mounts for attaching a lens to a video camera: C, CS, M12.
- The C mount is rarely used anymore. C lenses can be mounted on a CS mount camera using a special ring.
- The CS mount is the most common type. CS lenses are not compatible with C cameras.
- The M12 mount is used for small lenses.
Iris adjustment (auto iris), ARD, ARD
The diaphragm is responsible for the flow of light onto the matrix: with an increased flow of light, it narrows, thus preventing the image from being overexposed, and in low light, on the contrary, it opens so that more light falls on the matrix.
There are two large groups of cameras: fixed aperture(this also includes cameras without it at all) and with adjustable.
The aperture can be adjusted in various models of video surveillance cameras:
- Manually.
- Automatically video camera using direct current, based on the amount of light hitting the sensor. This automatic iris adjustment (ADA) is referred to as DD (Direct Drive) or DD/DC.
- Automatically a special module built into the lens and tracking the light flux passing through the relative aperture. This method of ARD in the specifications of video cameras is designated as VD (Video Drive). It is effective even when hitting the lens directly sun rays, but surveillance cameras with it are more expensive.
Electronic shutter (AES, shutter speed, shutter speed, shutter)
Different manufacturers may refer to this parameter as an automatic electronic shutter, shutter speed or shutter speed, but essentially it means the same thing - the time during which light is exposed to the matrix. It is usually expressed as 1/50-1/100000s.
The action of the electronic shutter is somewhat similar to automatic iris adjustment - it adjusts the light sensitivity of the matrix to adjust it to the light level of the room. In the picture below you can see the image quality in low light conditions at different shutter speeds (the picture shows the manual setting, while AES does it automatically).
Unlike ARD, adjustment occurs not by adjusting the light flux entering the matrix, but by adjusting the shutter speed, the duration of the accumulation of electrical charge on the matrix.
However the capabilities of the electronic shutter are much weaker than automatic iris adjustment, Therefore, in open spaces where the lighting level varies from twilight to bright sunlight, it is better to use cameras with ADS. Video cameras with an electronic shutter are optimal for rooms where the light level changes little over time.
The characteristics of the electronic shutter differ little between different models. A useful feature is the ability to manually adjust the shutter speed (shutter speed), since in low light conditions low values are automatically set, and this leads to blurred images of moving objects.
Sens-UP (or DSS)
This is a function of accumulating the charge of the matrix depending on the level of illumination, i.e. increasing its sensitivity at the expense of speed. Necessary for shooting high-quality images in low-light conditions, when tracking high-speed events is not critical (there are no fast-moving objects at the object of observation).
It is closely related to the shutter speed (shutter speed) described above. But if the shutter speed is expressed in time units, then Sens-UP is expressed in terms of the shutter speed increase factor (xN): the charge accumulation time (shutter speed) increases by N times.
Permission
We touched on the topic of CCTV camera permissions a little in the last article. Camera resolution is, in fact, the size of the resulting image. It is measured either in TVL (television lines) or in pixels. The higher the resolution, the more detail you will be able to see in the video.
Video camera resolution in TVL- this is the number of vertical lines (brightness transitions) placed horizontally in the picture. It is considered more accurate because it gives an idea of the size of the output image. While the resolution in megapixels indicated in the manufacturer's documentation can mislead the buyer - it often refers not to the size of the final image, but to the number of pixels on the matrix. In this case, you need to pay attention to such a parameter as “Effective number of pixels”
Resolution in pixels- this is the horizontal and vertical size of the picture (if it is specified as 1280x960) or the total number of pixels in the picture (if it is specified as 1 MP (megapixel), 2 MP, etc.). Actually, getting the resolution in megapixels is very simple: you need to multiply the number of horizontal pixels (1280) by the number of vertical pixels (960) and divide by 1,000,000. Total 1280×960 = 1.23 MP.
How to convert TVL to pixels and vice versa? There is no exact conversion formula. To determine the video resolution in TVL, you need to use special test tables for video cameras. For an approximate representation of the ratio, you can use the table:
Effective pixels
As we said above, often the size in megapixels indicated in the characteristics of video cameras does not give an accurate idea of the resolution of the resulting image. The manufacturer indicates the number of pixels on the camera matrix (sensor), but not all of them are involved in creating the picture.
Therefore, the parameter “Number (number) of effective pixels” was introduced, which shows exactly how many pixels form the final image. Most often it corresponds to the real resolution of the resulting image, although there are exceptions.
IR (infrared) illumination, IR
Allows shooting at night. The capabilities of the matrix (sensor) of a video surveillance camera are much higher than those of the human eye - for example, the camera can “see” in infrared radiation. This property began to be used for filming at night and in unlit/dimly lit rooms. When a certain minimum illumination is reached, the video camera switches to shooting mode in the infrared range and turns on the infrared illumination (IR).
IR LEDs are built into the camera in such a way that the light from them does not fall into the camera lens, but illuminates its viewing angle.
Image captured in low light conditions using infrared illumination, always black and white. Color cameras that support night photography also switch to black and white mode.
IR illumination values in video cameras are usually given in meters - that is, how many meters from the camera the illumination allows you to get a clear image. Long range IR illumination is called IR illuminator.
What is Smart IR, Smart IR?
Smart IR illumination (Smart IR) allows you to increase or decrease the power of infrared radiation depending on the distance to the object. This is done to ensure that objects that are close to the camera are not overexposed in the video.
IR filter (ICR), day/night mode
The use of infrared illumination for filming at night has one peculiarity: the matrix of such cameras is produced with increased sensitivity to the infrared range. This creates a problem for shooting in the daytime, since the matrix registers the infrared spectrum during the day, which disrupts the normal color of the resulting image.
Therefore, such cameras operate in two modes - day and night. During the day, the matrix is covered by a mechanical infrared filter (ICR), which cuts off infrared radiation. At night, the filter moves, allowing the rays of the infrared spectrum to freely enter the matrix.
Sometimes switching the day/night mode is implemented in software, but this solution produces lower-quality images.
The ICR filter can also be installed in cameras without infrared illumination - to cut off the infrared spectrum in the daytime and improve video color rendition.
If your camera doesn't have an IGR filter because it wasn't originally designed for night photography, you can't add night shooting functionality to it simply by purchasing a separate IR module. In this case, the color of daytime video will be significantly distorted.
Sensitivity (light sensitivity, minimum illumination)
Unlike cameras, where light sensitivity is expressed by the ISO parameter, the light sensitivity of video surveillance cameras is most often expressed in lux (Lux) and means the minimum illumination in which the camera is capable of producing a video image good quality- clear and noise-free. The lower the value of this parameter, the higher the sensitivity.
Video surveillance cameras are selected in accordance with the conditions in which they are planned to be used: for example, if the minimum sensitivity of the camera is 1 lux, then it will not be possible to obtain a clear image at night without additional infrared illumination.
| Terms | Light level |
| Natural light outside on a cloudless sunny day | over 100,000 lux |
| Natural light outside on a sunny day with light clouds | 70,000 lux |
| Natural light outside in cloudy weather | 20,000 lux |
| Shops, supermarkets: | 750-1500 lux |
| Office or store: | 50-500 lux |
| Hotel halls: | 100-200 lux |
| Vehicle parking, warehouses | 75-30 lux |
| Twilight | 4 lux |
| Well-lit highway at night | 10 lux |
| Spectator seats in the theater: | 3-5 lux |
| Hospital at night, deep twilight | 1 suite |
| Full moon | 0.1 - 0.3 lux |
| Moonlight night (quarter moon) | 0.05 lux |
| Clear moonless night | 0.001 lux |
| Cloudy moonless night | 0.0001 lux |
The signal to noise ratio (S/N) determines the quality of the video signal. Noise in video images is caused by poor lighting and appears as colored or black and white snow or grain.
The parameter is measured in decibels. The picture below shows quite good image quality already at 30 dB, but in modern cameras, to obtain high-quality video, S/N should be at least 40 dB.
DNR Noise Reduction (3D-DNR, 2D-DNR)
Naturally, the problem of noise in video did not go unnoticed by manufacturers. On at the moment There are two technologies for reducing noise in the picture and correspondingly improving the image:
- 2-DNR. Older and less advanced technology. Basically, only noise from the near background is removed; in addition, sometimes the image is slightly blurred due to cleaning.
- 3-DNR. Latest technology, which works according to a complex algorithm and removes not only near noise, but also snow and grain in the distant background.
Frame rate, fps (stream rate)
The frame rate affects the smoothness of the video image - the higher it is, the better. To achieve a smooth picture, a frequency of at least 16-17 frames per second is required. The PAL and SECAM standards support frame rates at 25 fps, and the NTSC standard supports 30 fps. For professional cameras, frame rates can reach up to 120 fps and higher.
However, it must be taken into account that the higher the frame rate, the more space will be required to store video and the more the transmission channel will be loaded.
Light compensation (HLC, BLC, WDR, DWDR)
Common video surveillance problems are:
- individual bright objects falling into the frame (headlights, lamps, lanterns), which illuminate part of the image, and because of which it is impossible to see important details;
- too much bright lighting in the background (a sunny street behind the doors of a room or outside a window, etc.), against which nearby objects appear too dark.
To solve them, there are several functions (technologies) used in surveillance cameras.
HLC - bright light compensation. Compare:
BLC - backlight compensation. This is achieved by increasing the exposure of the entire image, causing objects in the foreground to become lighter, but background It turns out too light, it is impossible to see the details.
WDR (sometimes also called HDR) - wide dynamic range. Also used for backlight compensation, but more effectively than BLC. When using WDR, all objects in the video have approximately the same brightness and clarity, which allows you to see in detail not only the foreground, but also the background. This is achieved due to the fact that the camera takes pictures with different exposures, and then combines them to obtain a frame with optimal brightness of all objects.
D-WDR - software implementation of wide dynamic range, which is slightly worse than full-fledged WDR.
Protection classes IK (Vandal-proof, anti-vandal) and IP (from moisture and dust)
This parameter is important if you are choosing a camera for outdoor video surveillance or in a room with high humidity, dust, etc.
IP classes- this is protection against the ingress of foreign objects of various diameters, including dust particles, as well as protection from moisture. ClassesIK- this is anti-vandal protection, i.e. from mechanical impact.
The most common protection classes among outdoor CCTV cameras are IP66, IP67 and IK10.
- Protection class IP66: The camera is completely dustproof and protected from strong water jets (or sea waves). Water gets inside in small quantities and does not interfere with the operation of the video camera.
- Protection class IP67: The camera is completely dustproof and can withstand short-term complete immersion under water or long periods of time under snow.
- Anti-vandal protection class IK10: The camera body will withstand a 5 kg load from a 40 cm height (impact energy 20 J).
Hidden areas (Privacy Mask)
Sometimes it becomes necessary to hide from observation and recording some areas that fall within the camera's field of view. Most often this is due to the protection of integrity privacy. Some camera models allow you to adjust the settings of several of these zones, covering a certain part or parts of the image.
For example, in the picture below, the windows of a neighboring house are hidden in the camera image.
Other functions of CCTV cameras (DIS, AGC, AWB, etc.)
OSD menu- the ability to manually adjust many camera parameters: exposure, brightness, focal length (if there is such an option), etc.
- shooting in low light conditions without infrared illumination.
DIS- camera image stabilization function when shooting in vibration or motion conditions
EXIR Technology- infrared illumination technology developed by Hikvision. Thanks to it, greater backlight efficiency is achieved: greater range with less power consumption, dispersion, etc.
AWB- automatic balance adjustment white in the image, so that the color rendition is as close as possible to the natural one visible to the human eye. Particularly relevant for rooms with artificial lighting and various light sources.
AGC (AGC)- automatic gain control. It is used to ensure that the output video stream from cameras is always stable, regardless of the strength of the input video stream. Most often, amplification of the video signal is required in low light conditions, and a decrease - on the contrary, when the lighting is too strong.
Motion detector- thanks to this function, the camera can turn on and record only when movement occurs on the object being monitored, and also transmit an alarm signal when the detector is triggered. This helps save space for storing video on the DVR, relieves the load on the video stream transmission channel, and organizes notification of personnel about a violation that has occurred.
Camera alarm input- this is the ability to turn on the camera and start recording video when any event occurs: the activation of a connected motion sensor or another sensor connected to it.
Alarm output allows you to trigger a reaction to an alarm event recorded by the camera, for example, turn on the siren, send an alert by mail or SMS, etc.
Didn't find the feature you were looking for?
We tried to collect all the frequently encountered characteristics of video surveillance cameras. If you did not find an explanation of some parameter here that is unclear to you, write in the comments, we will try to add this information to the article.
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