One of the first concepts that a person learns when he begins to take a more serious approach to the process of photographing is. The device in the lens through which the light passes is called the diaphragm. Depending on its size, we can get a certain depth of field. A large aperture creates a shallow depth of field, and a narrow one, respectively, is responsible for a larger one. Let's take a closer look at this fundamental concept in photography, so that we never get confused and know exactly what can be achieved as a result of applying certain diaphragm size values in practice.
1. Double effect
Aperture is measured using the "f-number"Sometimes referred to as “f-stop”, it shows the diameter of the hole. It must be remembered that a smaller f-number corresponds to a larger open aperture, in which more light falls on the photosensitive element, while a higher f-number means a narrower aperture (less light).
The base number of aperture is one. Although there are not so many lenses in the world, in which the aperture can open up to 1, nevertheless, they exist. Multiplying by 1.4, we get the standard diaphragm row: 1; 1.4; 2; 2.8; 4, etc. each subsequent number indicates that the amount of light passing through the lens has almost doubled or decreased. That is, a shot at 2.8 with a shutter speed of 1/60 second will be illuminated as well as a shot at 4 with a shutter speed of 1/30. The greater the number of apertures, the stronger it closes and the image is displayed with less light.
The full range of aperture values is as follows: f / 1.4; f / 2; f / 2.8; f / 4; f / 5.6; f / 8; f / 11; f / 16; f / 22 and f / 32. Most modern cameras allow you to control the diaphragm in 1/3 stop increments, so when adjusting the aperture on a modern camera between the numbers 2.8 and 4.0, you can find such intermediate values as 3.2 and 3.5.
Understanding how double throughput works when the aperture number changes by 1 stop useful when adjusting exposure and choosing shutter speed and / or sensitivity settings. The difference in the exposure of the frame when opening the aperture from f / 8 to f / 5.6 as when changing the sensitivity of ISO 100 to 200 will be the same - i.e. one foot lighter in both cases. Similarly, you can get a picture one foot lighter if the sensitivity is kept the same, and the exposure is adjusted with a shutter speed, changing 1/125 to 1/60 s. And it will be the same result, as if changing the aperture from f / 8 to f / 5.6.
2. F-number
Many novice photographers are confused by the fact that a small aperture has a larger f (or f / number) value, while large aperture values have small f-numbers. The thing is that the aperture value is the ratio of the diameter of the exit pupil of the lens to its focal length, expressed by a fraction with a numerator equal to one. In the photo, instead of a unit, the Latin letter f is often used, which specifies the purpose of the fraction: for example, the relative aperture 1 / 5.6 is indicated by f / 5.6. From this it can be seen that for different lenses the same aperture value will denote a different diameter. For example, the f / 11 aperture on a 100 mm (100/11) lens will be 9.09 mm. For a 50mm lens, the same aperture will already be (50/11) equal to 4.54 mm.
Now it is clear that they cannot pass through the same amount of light through an opening of 9.09 mm and 4.54 mm.
3. Diffraction
Diffraction is the curvature of light rays when they pass along the edge of the diaphragm's petals. When the diaphragm is closed, to increase the depth of field, diffraction increases, which softens the image, since the rays do not converge at one point on the sensor surface, but are refracted and, therefore, give a soft image. To obtain a fundamentally clear image over the entire area of the picture, they usually do not use the smallest possible aperture value when shooting.
4. Optimum aperture
For most lenses, it is characteristic that at the maximum open aperture it is difficult to achieve maximum sharpness in the frame. As a rule, the diaphragm is slightly covered. The optimal aperture value for each lens is obtained experimentally. It is necessary to follow the diffraction - at what values of f it will be the minimum acceptable for the photographer, the aperture value can be considered optimal for work.
To test the lens the important point is to use a strong tripod for the camera. The need for this is dictated by the fact that it is necessary to focus on the same place. After the test shots are taken, view them at 100% magnification on the monitor screen. You can choose the sharpest and, by checking the EXIF data, determine at what aperture one photo was taken. This will be the optimal aperture value for this lens.
by Helena Kuchynková
5. Sharpness of the lens and bokeh - feel the difference
Bokeh (boke) is a Japanese word and means artistic background blur. A good side is considered to be one that, as it were, rounds out the main points of the image, rather than leaving the sides of objects that are out of focus sharply outlined, for example, forming a clear hexagon. Bokeh should be attributed to the properties of the lens, the result of the work of its optical elements and aperture, and not to the capabilities of the camera with which the photo was taken.
by Tillmann van de Maan
The best bokeh is obtained from those lenses that have a greater number of petals and rounded edges.
6. AF and aperture
For a start, it will be enough to know that the wider the angle of the rays of light, the more accurate the autofocus will be. In the above diagram, the angle of the rays received from the f / 2.8 lens (blue lines) will be greater than from the f / 4 lens (red lines), which in turn is greater than from the f / 5.6 lens (yellow lines ). When using a lens with a maximum f / 8 aperture, only the most accurate sensors are able to work, but the focus will be slower and less accurate. It is for this reason that f / 5.6 lenses stop autofocusing when a photographer tries to use a teleconverter, which reduces their maximum aperture ratio to f / 8 or f / 11.
This, of course, is not all the knowledge that an experienced user needs; nevertheless, for the beginning it should be very well oriented in these technical intricacies. We will continue to give lessons on the fundamental theory of photography - stay with us, share lessons with friends and enjoy your creativity.
Along with the camera, the lens is an essential part of a video surveillance system. The angle of view of the camera, the sensitivity and resolution of the entire system depends on the choice of lens.It often happens that in pursuit of a cheap economy, the consumer installs a lens with poor optical characteristics on a high-end camera, and as a result the image loses crucial details that, alas, cannot be subsequently restored by any digital signal processing.
Lens specifications
Objectives can be classified according to the diameter of the bore, according to the presence and method of adjusting the aperture and (or) focal length, according to luminosity, resolution, the presence of aspherical lenses and some other features.
Luminosity
The aperture ratio of the lens determines its F-number, which characterizes the brightness of the resulting image. It is equal to the ratio of the focal length to the maximum diameter of the aperture (aperture). The smaller the value of the F-number, the more high-aperture is the lens. The return value is called the relative aperture. It is clear that with a comparable aperture size, the aperture and the relative aperture of long-focus lenses are always smaller (and the F-number is correspondingly larger) than that of short-focus lenses.
Resolution
The resolution of the lens characterizes its ability to create separate images of two closely spaced points or lines of the measuring world projected or viewed through this lens. Since the limiting resolution of the lens is limited by diffraction on it, the empirical Rayleigh criterion for the diffraction resolution was introduced in order to exclude subjectivity. In it, a minimum between them with a level of 0.8 is considered sufficient for distinguishing two maxima, that is, the minimum image contrast at which points (or lines) are considered resolvable is 20%.
The resolution of the lens is measured in lines per millimeter and is determined by the ratio of the maximum possible number of white stripes alternating with black, which this lens can project to the working area of the CCD with a contrast of 20% to the width of this zone. The resolution of most lenses for security television ranges from 50 to 150 lines / mm. For megapixel IP cameras, high-resolution lenses are available. However, the resolution of cheap mini lenses can be significantly less than 50 lines / mm. When using optics of this kind, the overall resolution of the system will most likely be limited to just the lens, which is unacceptable in most cases. Lens resolution is uneven across the field. The maximum and declared value is provided at the center of the aperture. Along the edges for good quality lenses, the resolution is reduced by 15-20%.
Types of fastening
According to the diameter of the mounting hole (mounting thread), the lenses can be divided into three large groups: C / CS-mount, with mounting thread M12 and with other thread sizes.
C-mount
The type of mount C-mount was the first standard, which appeared before the era of CCD cameras. It is characterized by a 1 inch (25.4 mm) thread diameter, 1/32 inch (0.79375 mm) pitch and the distance of the locking plane of the lens rim to the image plane on the CCD matrix (working length or back focus) - 0.69 in. (17,526 mm). With the beginning of widespread use in video surveillance of small-format CCD matrices, it became possible to significantly reduce the apertures of lenses and the dimensions of cameras, and therefore the new mounting standard CS (Small, Small C) was adopted. It differs from the old standard only in the reduced distance from the lens to the CCD sensor. Now it is exactly 12.5 mm. Thus, the camera with the lens has become shorter by more than 5 mm. Given that the thread has remained exactly the same, you can install old C-lenses on new CS cameras using a 5 mm thick adapter ring (photo 1) and thus moving the lens back to properly adjust the back focus.
Use the new CS-lens with the old C-camera is impossible. True, now the compatibility of standards is not too important - the vast majority of optics and almost all full-size cameras on the CCTV market are made according to the CS standard. For conventional spherical CS optics, the typical values of the number F are 1.2, 1.4, 1.6. High-quality aspherical lenses usually have an F equal to 0.8-1.0, and the most high-aperture - up to 0.5.
Photo 1. Adapter ring for installing a C-lens on a CS-camera
M12 thread
The second most common are lenses with mounting threads M12 and with a step of 0.5 mm (less often 1 mm). This standard became popular at the same time as the mass appearance in the second half of the 1990s. miniature unpacked cameras, for which the dimensions (first of all, the diameter) and the price of CS lenses already seemed too large. Then came the small-sized case square, cylindrical and dome cameras, and the number of M12 lenses, usually supplied with cameras, almost exceeded the number of CS lenses. Ml2 lenses are basically very simple (and therefore cheap) lenses without any adjustments. The typical F-number of the standard focal length series (2.45-16 mm) of these lenses is 2.0. Over time, the range of optics with a landing size M12 expanded - not only ordinary board and pin-hole, but also more complex lenses with an automatic diaphragm and variable focal length are produced. Of course, the luminosity and resolution of such lenses are usually worse than that of the "full-size" counterparts, therefore, where the dimensions do not matter much, it is better not to use them. Pin-hole lenses are characterized by F-numbers from 2.0 (for multi-lens) to 3.5-5.0 (for single-lens).
M7 thread
With the beginning of the new century, the miniaturization trend continued, some CCD cameras decreased to the size of 20x20 mm, in addition, single-crystal CMOS cameras with sizes up to 8x8 mm appeared. Of course, optics manufacturers immediately made suitable lenses for them. One of the new standards was the M7 thread, and, very likely, in 3-5 years another technological breakthrough will require even smaller sizes.
Aperture Adjustment Types
By the method of adjusting the aperture lenses can be divided into three groups: fixed, manual and automatic aperture.
The diaphragm is a hole (window) that regulates the diameter of the light beam passing through the lens. Obviously, the larger the diameter of such an aperture, the more light will fall on the CCD camera array and the lower the illumination this camera will be able to “show” normally. Fixed aperture The simplest lens is a fixed aperture lens (see photo 2). Sometimes they say about him - “without a diaphragm”, which, of course, is wrong, because any optical device has an aperture (aperture), but there is such a design that there is no possibility of changing it. Such a lens usually has no adjustments, it has no moving parts, which means it is very cheap (from the manufacturer’s tens of cents to a few dollars - in Moscow for a regular M12 lens), reliable (provided the manufacturer observes the technology) and is extremely simple. installation and maintenance. If we are talking about optics with an installation thread of M12 and less, then in most cases it comes with the camera and does not need to be set up at all. In the case of replacement of such a lens, you just need to achieve a clear image on the monitor, screwing and twisting it in the camera holder.
Photo 2. Fixed aperture lenses
Manual adjustment
Consider lenses with manual adjustment of the aperture (see photo 3). The mechanism usually consists of several petals that can move when the diaphragm ring is rotated on the lens barrel.
With an open diaphragm, the typical values of the F-number are 1.2,1.4,1.6. At the opposite extreme position of the adjustment ring for many lenses, the aperture closes completely and the image is not formed. Lens lenses remain motionless. This allows you to set the desired value of the aperture when you install the camera directly on the object, and, if necessary, change it during operation without changing the lens and usually even without dismantling the camera. Such lenses, of course, are much more convenient than those with a fixed aperture, as they allow you to fine-tune the lens, achieving an acceptable compromise between depth of field (minimum aperture) and camera sensitivity (maximum aperture) directly at the camera installation site, under specific conditions. Of course, when the illumination level changes, such a lens cannot automatically “move or open the blinds”, therefore the main place of application for optics with a manual diaphragm is rooms, moreover, with a small window area and preferably not located on the south side. The electronic shutter may well “cope” with relatively small differences in illumination in such rooms by changing the exposure time of the CCD array.
Photo 3. Manual iris lens
Auto iris
Auto-iris lenses are best suited for outdoor, outdoor use (photo 4). The diaphragm petals are moved in such lenses using a microdrive controlled by an electronic circuit located inside the lens or camera. In fact, the autodiaphragm mechanism is a negative electron-mechanical feedback. At the same time, the main task is to “keep” the video signal level of the camera at the nominal level. The typical stated range of relative aperture changes is usually from 1 / 1.2 or 1 / 1.4 (fully open diaphragm) to 1/360 (fully closed diaphragm). This gives a change in the illumination on the matrix of more than 30,000 times. Such a range of change of the diaphragm cannot be ensured only due to its decrease as a result of diffraction and technological limitations. To ensure the required range, an absorbing coating with a variable density increasing towards the center of the aperture (the so-called ND filter) is applied to the central part of the lens.
Photo 4. Lens with automatic aperture
Diaphragm control. VD and DD lenses
If the electronic "stuffing" is placed in the lens housing, then the power supply and the video signal without a sync mixture are supplied from the camera to the lens. When the video signal level drops below the nominal, a control voltage is formed to open the aperture blades. If the video signal increases, the aperture closes.
The LEVEL control allows you to change the opening of the aperture at the nominal level, that is, it actually sets the brightness of the image. The ALC controller on the lens allows you to change or set the average value of the illumination at which the nominal level of the video signal is provided. This scheme is the most flexible and efficient diaphragm, it was called Video Drive (VD). If the electronic control circuit of the diaphragm is located inside the camera, a direct current is applied to the lens that drives the drive. This type of lens is called Direct Drive (DD), or DC (controlled by direct current). Obviously, the principle of the auto iris is the same in both cases.
Most modern cameras have a switch that allows you to control both VD and DD lenses. Given that the cost of DD lenses is somewhat lower, they are often used for budget decisions. However, the electronic diaphragm control circuit in the camera is usually somewhat simplified compared to the circuit in the VD-lens: for example, the ALC regulator is often missing. This adjustment allows you to set useful in some cases, the mode when the diaphragm will not “close” when bright point objects (lanterns, car headlights, highlights) come into view, allowing for the loss of some information near them due to blooming (“flooding with white”) while maintaining sufficiently visible dark zones "pictures". Many universal VD / DD cameras do not have such a regulator; therefore, in critical and difficult cases, we can recommend smart lenses with aperture control video signal (VD type) for the most accurate setting of the camera-lens system.
Many auto iris lenses have the ability to remotely control aperture. The operator controls the aperture manually from the remote and can optimally adjust the camera to work in different light conditions. Currently this mode is rarely used.
An automatic diaphragm, certainly very useful on the street, is not always necessary, and sometimes harmful indoors. The fact is that when adjusting the aperture of the camera, the depth of field changes, which in some cases can be fraught with the loss of critical information. Therefore, in case of stable and sufficiently good illumination, it is better to use optics with a manual diaphragm and an electronic shutter mode on the camera.
Focal length
The most important characteristic of the lens is the focal length. Along with the format of the CCD matrix, it uniquely determines the camera angle of view, and also gives the possibility of changing it.
The range of focal lengths used in CCTV is very large - from 1.4 mm (fisheye lenses) to meters (for the most expensive long-focus zoom lenses). The angle of view can be from several angular minutes to almost 180 degrees horizontally. If the “super-wide-angle” optics, even if not of the highest quality, is very widely distributed (let us remember the simplest video eyes), then lenses with meter focal lengths are so expensive and require such powerful fixture that their use is extremely limited.
In the simplest case, the focal length of the lens is constant. It lacks a mechanism for moving the lenses, which allows the lens to be made cheaper at high optical characteristics. For a long time, it was precisely such optics that were installed both on miniature television cameras and on cameras of the classical layout.
Varifocal lenses
Now the situation has changed - it is more convenient for the consumer to work with varifocal lenses, making it possible to change the focal length and, accordingly, the angle of view. This greatly simplifies the life of the installer, however, the manufacture of high-quality "varifocal" is a very difficult task, and not every manufacturer copes with it. After all, such a lens has movable lenses, which requires much greater precision in the manufacture of the optical system than, for example, in the manufacture of an autodiaphragm mechanism. Therefore, it is worth it when buying varifocal lenses to be safe and buy a slightly more expensive, but obviously high-quality “brand” optics, without being tempted by super-cheap noname lenses.
The multiplicity of changes in focal lengths for varifocal lenses is usually from 2 to 10.
If you put a remote control drive on a varifocal lens, it will automatically turn into a zoom lens - one of the most powerful CCTV tools (photo 5). Now it is not uncommon for high-speed zoom lenses that allow you to quickly “enlarge” a desired object by 20–30 times. In such lenses, the focal length (ZOOM function), focusing (FOCUS) and aperture (IRIS) are usually remotely changed. Using a camera with a zoom without a rotator is unreasonable in most cases - the “hitting” will always be carried out at one point, so the integrated Speeddome kits, including a camera, a zoom lens, a high-speed turntable and a dome housing, have become very popular. Most of the currently produced zoom lens is part of such products.
Photo 5. Lens-zoom
Types of lenses
By the type of lenses used lenses are divided into spherical and aspherical.
In the first case, the lens consists of inexpensive spherical lenses, and in the second, lenses of a more complex shape are used. The main advantages of aspherical optics include a large aperture ratio (the F number usually does not exceed unity), as well as the absence of so-called "spherical aberrations" (distortions), which makes it possible to abandon lenses correcting these distortions, and, as a result, to increase the transmittance, reduce mass and the dimensions of the lens.
At night, when using infrared illumination, there is some defocusing of the image due to a change in wavelength. There are lenses free from this flaw. They allow you to get a focused image without reconfiguring the system when the scene is illuminated with radiation with a wavelength of up to 950 nm. Following the cameras, some lenses acquired a mechanically removable light filter that “cuts off” IR radiation in bright light and transmits it in the dark.
CCTV market
A special group should include pin-hole miniature lenses with pupil removal, intended mainly for concealed installation (photo 6). Such a lens can "look" through a hole smaller than the diameter of the input lens (about 1 mm in diameter). Cheap single-lens lenses with a small entrance pupil, with which most miniature television cameras are completed, do not have a pupil at all and, strictly speaking, cannot be called pin-hole.
Photo 6. Pin-hole lenses
Optical production is one of the most complex both in terms of design and manufacturing technology. The recognized leaders in this field have long been considered three countries - Germany, Japan and Russia. As for lenses for CCTV, while the domestic industry has limited itself to releasing relatively small lots of pin-holes and assembling lenses based on imported components, as a result, the significantly wider market of CS lenses was mainly occupied by Japanese products.
In the last decade, the Koreans have seriously pressed the position of the Japanese, and after them the Chinese. The quality of work of the latter, especially with regard to varifocal lenses, often leaves much to be desired. Negligence in the manufacture of printed circuit boards of cameras and the installation of elements usually does not entail such consequences as inaccuracy in the assembly of optics. Therefore, you need to be cautious when buying very cheap lenses, even if they are very similar to real ones. And if, with a slight shaking from the inside, the roar of dangling lenses is heard, then the supplier offering such products has to run.
In conclusion, I would like to express the hope that the leading Russian optical-mechanical enterprises and traditionally high-quality Russian optics will take on the CCTV market and take a worthy place in this area, such.
M. Arsentev
Security systems №1, 2008.
1. What is a diaphragm
The aperture (aperture) is a relative aperture of the lens that allows you to adjust the flow of light entering the matrix of a digital camera and control the depth of the sharply depicted space.
2. The diaphragm petals
The diaphragm consists of thin metal petals that cover or open a hole for light. Depending on the lens model, there may be more or less. The number of petals determines the shape of the orifice of the diaphragm — it can be close to a circle, or it can be hexahedral. The more petals, the hole is rounder, and the lens pattern is more beautiful. For example, when shooting on a lens with a large number of petals, in a zone of non-sharpness, even round spots are formed, and not geometric shapes resembling nuts.
Modern lenses have rounded petals, despite their small amount, provide a soft and beautiful background blur.
3. Aperture number, steps, aperture values
The f-number is the ratio of the focal length of the lens to the diameter of the diaphragm, denoted as f / x, where x is its numerical value. The diaphragm controls the flow of light entering the photosensitive elements of the matrix. The larger the f-number, the smaller the transmissive aperture, and vice versa, the smaller the f-number, the larger the opening, respectively, more light passes. For clarity: f / 16 - closed diaphragm, f / 1.4 - open.
The aperture values are measured in steps.
| 1.0 | 1.4 | 2 | 2.8 | 4 | 5.6 | 8 | 11 | 16 | 22 |
Each stage differs from the previous one by 1.4 times, while the amount of light entering the camera matrix is changed twice.
For a more accurate exposure of the exposure in modern cameras there are intermediate aperture values equal to 1/3 of a stop:
| 1.0 | 1.1 | 1.2 | 1.4 | 1.6 | 1.8 | 2 | 2.2 | 2.5 | 2.8 | 3.2 | 3.5 | 4 | 4.5 | 5 | 5.6 | 6.3 | 7.1 | 8 | 9 | 10 | 11 | 13 | 14 | 16 | 18 | 20 | 22 | 25 | 29 | 32 |
4. Depth of field
The depth of the sharply depicted space (DOF) is the area in which the subject will be depicted sharply, and everything that goes beyond it is blurry.
Depth of field depends on the following parameters:
- diaphragm
the smaller the f-number (open diaphragm), the shallower the depth of field, at the closed diaphragm the depth of field will be across the entire frame depth; - lens focal length
the smaller the focal length of the lens (for example, wide-angle), the greater the depth of field, the depth of field on the long-focus lenses is noticeably reduced; - distance to the subject
the smaller the distance from the camera to the subject, the smaller the depth of field, the longer the distance, the greater the depth of field.
The influence of the diaphragm on the depth of field.
5. The formula for calculating the depth of field
R1 - the front border of the sharply depicted space;
R2 - the rear border of the sharply depicted space;
R is the distance in meters, which is aimed at sharpness;
f is the focal length of the lens (absolute, not equivalent), the value in meters is substituted into the formula;
K is the denominator of the relative aperture of the lens (aperture number);
z is the diameter of the permissible circle of unsharpness, for negatives with a format of 24x36 mm, equal to 0.03-0.05 mm (the value in meters is substituted into the formula).
6. Diaphragm control
The primary role of the diaphragm is to control the depth of the sharply depicted space. The aperture value is set depending on the goal. For example, when shooting landscapes, when sharpness should be across the entire field of the frame, the optimal aperture value would be f / 11 - f / 16, when shooting a portrait where you need to focus on the subject, the value - f / 1.2 - f / 2.5 will do. while the main object will be in the zone of sharpness, and the background is very blurred. When shooting on an open aperture, certain difficulties may arise, given that the zone of sharpness is only millimeters, a slight change in the angle of inclination of the camera entails a shift in focus.
What should be considered. On a fully open aperture, chromatic aberrations (color distortions) may appear, and excessive closure of the diaphragm leads to diffraction (loss of sharpness).
Lenses, depending on their technical characteristics, have a different minimum aperture value. The most high-aperture lenses are with a fixed focal length - f-number from f / 1.2 to f / 2.8. On lenses with variable focal length, it is often possible to see a threshold of f values, for example, 18-55 f3.5-5.6. This means that with a focal length of 18mm, the minimum aperture value will be 3.5, while for 55mm it will be 5.6.
The advantages of high-aperture lenses:
- high-aperture optics allows you to work in low light conditions without the use of additional equipment and at low ISO;
- a small number of lenses in the design of the lens, which provides the best image quality;
- soft and beautiful bokeh on the open aperture.
The most high-aperture lens is Carl Zeiss 50mm f / 0.7, released by NASA.
The most important element of any video surveillance system is a video camera. The quality and performance of the entire system depends on the quality of the image it forms. In fact, it is the video camera that determines how clear the resulting image will be, how important the details of the image are distinguishable in it, whether the sharpness will remain sufficient when showing fast-moving objects of observation.
A modern camera designed for remote video surveillance is a rather complex technical device, characterized by many parameters and properties. Among them, the ability to control the aperture of the lens is a significant factor in determining the depth of field of the resulting image.
The position of the diaphragm, which specifies the size of the relative aperture of the lens, determines the number of diameters of the open part of the lens that fit in its focal length. The greater this value, the less light penetrates into the camera and the greater the depth of field of the formed image. The required position of the diaphragm is determined by many factors, the most important of which are the photosensitivity of the used CCD and the level of illumination of the object of observation.
The higher the sensitivity and illumination, the more the aperture should be closed, the greater will be the depth of field. Of course, you can equip your camcorder with manual lens iris control. But in this case, the operator of the security surveillance system is burdened by the additional burden of setting up the camera. In practice, it is more preferable to entrust the function of controlling the position of the diaphragm to the automatics. So in modern cameras appeared automatic aperture control (abbreviated ARD). This electronic means ensures that the CCD is maintained at an optimal level of illumination, which guarantees the maximum possible depth of field of the resulting image under these conditions. The ARD system measures the intensity of the input light flux and automatically sets the size of the relative aperture of the lens that is currently required.
There are two options for automatic control of the diaphragm:
- according to the value of direct current (DC)
- video signal VIDEO.
When installing the camera indoors, manual adjustment of the aperture is allowed, since the range of variation in illumination is not wide. When installing the camera outdoors and in conditions of significant changes in light, it is necessary to use a lens with auto iris.
Dealing with the technical features of video cameras may not be easy. If you find it difficult to choose a video camera, call us! Our staff will help you with useful recommendations and expert advice!
Aperture, depth of field control
Card file for August in the middle group
Business Card Group Presentation
Planning walks in November
The number of nouns