In most countries of the world, camcorders have long become commonplace. People take them to school performances, sporting events, family gatherings and even childbirth. In a place popular with tourists, they can be seen everywhere. Video cameras have gained a strong position in the United States, Japan and many other countries, since they are a very popular technology.
But how can such a small device do so much? Those born before the 1980s are surprised that high-quality models are now easily accessible, and that they are so easy to use. This article discusses the principle of operation and the design of the camcorder.
Basic design
A conventional analog video camera consists of two main parts:
- Section, including CCD, lens and zoom, focus and aperture control engines;
- reduced size VCR.
The principle of the video camera is that it receives visual information and turns it into an electronic signal. The VCR is similar to a regular one connected to a TV: it receives a signal, and it records it on a tape.
The third component, the viewfinder, also receives a video image, so the user can see what he is shooting. This is a small black and white or color display, but many modern models are additionally equipped with large full-color LCD screens. There are many formats of analog video cameras with many additional functions, but the described design is basic. They differ in which cassettes they use.
The device and principle of operation of digital video cameras are similar to analog ones, but they have an additional element that converts information into data bytes. Instead of recording a video signal as a continuous sequence of magnetic pulses, it is stored as zeros and ones. Digital camcorders are popular because they make it easy to copy video without losing any information. The analogue record “disappears” with each copy - the original signal is not reproduced accurately. Digital video information can be downloaded to a computer, where it can be edited, copied, sent by e-mail, etc.
Image sensor
Like a camera, a video camera “sees” the world through a lens. Optics is needed to focus the light from the stage onto the film treated with photosensitive chemicals. Thus, the camera captures what is in front of it. It collects more light from bright areas of the scene and less from dark. The lens of the camcorder also serves to focus, but instead of a film, it uses a small semiconductor image sensor. This sensor detects light using an array of millions of tiny photodiodes. Each of them measures the number of photons that hits a certain point, and translates this information into electrons (electric charges): a brighter image is represented by a higher charge, and a darker one is represented by a lower one. Just as an artist paints a scene, highlighting dark areas with light, the sensor creates a video by recording light intensity. During playback, this information controls the brightness of the display pixels.
Of course, measuring the luminous flux gives only a black and white image. To get color, you need to determine not only the overall level of illumination, but also the levels for each color. The full range can be recreated by combining just 3 of them - red, green and blue. Therefore, the principle of operation of video cameras is based on the use of only these colors.
In some models, the signal is divided into 3 variants of the same image for the levels of red, green and blue light. Each of them is captured by its own chip. Then they are folded and the primary colors are mixed to produce a full color image.
This simple method allows you to get rich video with high resolution.
Photodiode CCDs are expensive and consume a lot of energy, and using 3 sensors significantly increases production costs. Most camcorders are equipped with only one sensor with constant color filters for individual photodiodes. A certain part of them measures only the levels of red, the other - green, and the rest - blue. The colors are distributed in a grid (for example, a Bayer filter) so that the processor of the camcorder can get an idea of the color levels in all parts of the screen. This method requires interpolation of the data arriving at each photodiode by analyzing the information received by its neighbors.
Signal conditioning
Since video cameras capture moving images, their sensors have additional fragments that are not found in digital camera sensors. To create a video signal, they must take many shots every second, which are then combined to give the impression of moving.
To do this, the camcorder captures the frame and interlaces it. Behind the image sensor is another sensor layer. For each field, video charges are transferred to it, and then sequentially transmitted. In an analog video camera, this signal is fed to a VCR, which records it (along with color information) on the video tape in the form of magnetic pulses. While the second layer is transmitting data, the first captures the next image.
The principle of operation of a digital-type video camera is basically the same, except that at the last stage, an analog-to-digital converter converts the signal into data bytes. The camera writes them to media, which can be magnetic tape, hard disk, DVD or flash memory. Interlaced digital models save each frame as two fields in the same way as analog ones. Progressive scan cameras record video frame by frame.
Lens
As mentioned earlier, the first step in recording a video image is to focus the light on the matrix. The principle of the camcorder lens is as follows. In order for the camera to record a clear picture of the object in front of it, it is necessary to focus the optics, that is, move it so that the rays coming from the subject fell exactly on the sensor. Like cameras, camcorders allow you to move the lens to focus light.
Autofocus
Most people need to move and shoot different objects at different distances, and constant refocusing is extremely difficult. That's why all camcorders have an auto focus device. This is usually an infrared ray that reflects off objects in the center of the frame and returns to the camera’s sensor.
To determine the distance to the object, the processor calculates how long it takes for the beam to reflect and return, multiplies this value by the speed of light and divides the product by two (because it traveled the distance twice - to the object and back). The camcorder has a small engine that moves the optics, focusing it to the calculated distance. Usually this works quite well, but sometimes you have to re-determine the distance - for example, when you want to focus on something not in the center of the frame, since autofocus responds to what is directly in front of the lens.
Optical and Digital Zoom
Camcorders are also equipped with a zoom lens. Thanks to this, you can bring the scene closer by increasing the focal length (between the optics and the film or sensor). A lens with optical zoom is a single unit that allows you to switch from one magnification to another. The zoom range indicates maximum and minimum magnification. To make it easier to use the zoom, most camcorders are equipped with an engine that moves the optics in response to pressing a button on the handle. One of the advantages of this is that you can easily control magnification without using a second hand. In addition, the motor moves the lens at a constant speed, and the zoom is smoother. However, the engine runs out of battery power.
Some camcorders have the so-called digital zoom. Users are not advised to use it, since it is not connected to the lens at all, but simply increases the part of the image captured by the sensor. In this case, permission is sacrificed, since only part of the sensor area is used. As a result, the video is less clear.
Exposition
One of the great features of the camera is its automatic adjustment to different light levels. The sensor is very sensitive to overexposure or underexposure, since the range of signals from each photodiode is limited. The camcorder controls their level and adjusts the aperture, reducing or increasing the flow of light through the lenses. The processor constantly maintains good contrast so that the images do not look too dark or blurry.
The principle of operation of surveillance cameras
Such cameras are useful to those who want to know what happens during their absence. The need for them can arise for various reasons. For example, parents may want to watch a sleeping child and reduce the risk of a dangerous fall from the crib. And the cameras around the house will allow you to see people who come to the front door and, perhaps, even help find the criminal who committed the hack.
The output signal of the camera is transmitted, processed, converted again into an image and, if necessary, recorded. You can transfer video over a coaxial cable or twisted pair cable, as well as over a wireless network. Signal processing is performed in a DVR, server or PC with a video capture card. The image is displayed on the monitor.
The principle of operation of outdoor surveillance cameras is that they are installed on gates, buildings, and other structures in order to monitor what is happening in real time. As a rule, these are large, noticeable devices, the very appearance of which allows outsiders to understand that they are under surveillance.
The principle of operation of wireless video cameras is based on broadcasting images over a wireless network. However, other devices such as Wi-Fi routers and mobile phones can interrupt their signal. In addition, wireless transmission may be intercepted, which is contrary to security objectives. Therefore, users are advised to make sure that there is strong signal encryption.
The principle of operation of hidden video cameras is based on the use of point-type lenses with an outlet a few millimeters and a wide viewing angle. This allows you to install them in household appliances and interior items.
Tips for choosing analog formats
Analog cameras record video and audio as an analog tape track. Experts do not recommend using them, because when copying, the quality of the image and sound inevitably decreases. In addition, a number of digital video camera functions are not available in analog formats. The main difference between the two is the type of cassette and the resolution. The main formats of analog video cameras include:
- VHS standard. This type of camera uses the same tape as conventional video recorders. This makes it easier to view the footage. Such tapes are inexpensive and provide a long recording time. The main disadvantage of the VHS format is the need for a bulky camcorder design. Resolution is 230–250 horizontal lines, which is the lower limit in devices of this type.
- VHS-C cameras use a standard VHS tape, but in a more compact cassette. Recording can be played back on a regular VCR, but this requires a full-sized adapter. In principle, the operation of a VHS-C format camcorder is similar to that of VHS. The smaller cassette size allows for more compact designs, but the recording time is reduced to 30–45 minutes.
- Super VHS cameras are about the same size as VHS because they use cartridges of the same format. The difference is that the recorded resolution is 380-400 lines. Such tapes cannot be played back on a VCR, but the camera itself can be connected directly to the TV.
- Super VHS-C is VHS compliant, but it's a more compact version that uses a smaller cartridge.
- 8 mm camcorders also feature small cassettes. This allows you to produce more compact models that provide a resolution that complies with the VHS standard, with slightly better sound quality. The recording time is about 2 hours.
- The Hi-8 standard is similar to the 8 mm, but provides a much higher resolution - about 400 lines.
Tips for choosing digital formats
The principle of operation of digital video cameras differs from analog ones in that the information in them is recorded in digital form, due to which the image is reproduced without loss of quality. Such a video can be downloaded to a computer, where it can be edited or published on the Internet. It has a much better resolution. The following formats are widely used:
- MiniDV features compact cassettes that hold 60–90 minutes of video material with a resolution of 500 lines. Cameras of this type are extremely light and compact. Capture still images.
- The Sony MicroMV format works the same, but uses smaller cassettes.
- Digital8 uses a standard Hi-8mm film for 60 minutes of recording. Models of this type are usually slightly larger than DV.
- DVD cameras save videos directly to small optical discs. The main advantage of this format is the recording of each session as a separate track. Instead of rewinding and fast rewinding, you can immediately go to the desired part of the video. In addition, DVD-cameras are quite close to MiniDV models, but can store more video - from 30 minutes to 2 hours.
- DVD-R and DVD-RAM are 3/4 of the size of DVD discs. The disadvantage is that you can record on them only once. They cannot be played on regular DVD players. Like MiniDV cassettes, you need to either use the camera as a player, or copy the movie to a different format.
- A memory card is the most popular way to record video. The clips are saved directly to solid state cards such as flash memory, memory stick or SD.
Finally
Today, everyone can buy an inexpensive camera, and editing programs simplify the processing process to such an extent that everyone is able to quickly master it.
Even low-quality analog models have many useful features that are easy to master and create high-quality films. Technology, which was once the exclusive domain of professional television, has become available to fans. The latest video cameras, of course, can offer a lot to those who want to capture a birthday or a concert, and to the beginners of ambitious video projects.