How big is the photosensitive original of professional DV?

This is a professional question. Ha ha.

There are two kinds of image sensitive devices in digital cameras: CCD and CMOS. The size of the image sensor, that is, the area of the photosensitive device, includes CCD and CMOS. The larger the area of photosensitive device, the larger the CCD/CMOS area, the more photons captured, the better the photosensitive performance and the lower the signal-to-noise ratio. CCD/CMOS is an element used for photosensitive imaging in digital cameras, which is equivalent to the film in traditional optical cameras.

The surface of photosensitive elements on CCD has the ability to store charges and is arranged in a matrix. When its surface feels the light, it will reflect the charge to the components, and the signals generated by all the photosensitive components on the whole CCD constitute a complete picture.

If you decompose CCD, you will find that the structure of CCD has three layers, the first layer is "microlens", the second layer is "dichroic filter" and the third layer is "photosensitive layer".

The first layer of "microlens"

We know that the key to digital camera imaging lies in its photosensitive layer. In order to expand the lighting rate of CCD, it is necessary to expand the light receiving area of a single pixel. However, the method of improving the lighting rate is also easy to reduce the image quality. This layer of "microlens" is equivalent to adding a pair of glasses in front of the photosensitive layer. Therefore, the photosensitive area is no longer determined by the opening area of the sensor, but by the surface area of the microlens.

The second layer is a "dichroic filter"

The second layer of CCD is the "dichroic filter". At present, there are two color separation methods, one is RGB primary color separation method, the other is CMYK complementary color separation method. These two methods have their own advantages and disadvantages. First of all, let's understand the concepts of two color separation methods. RGB is a method for separating three primary colors. Almost all the colors that human glasses can recognize can be composed of red, green and blue. The three letters of RGB are red, green and blue respectively, which shows that RGB color separation is formed by adjusting the colors of these three channels. Let's talk about CMYK, which is composed of four channels of colors, namely cyan (C), magenta (M), yellow (Y) and black (K). In the printing industry, CMYK is more suitable, but its adjusted color is not as much as RGB.

The advantage of primary color CCD is sharp image quality and true color, but the disadvantage is noise. Therefore, we can notice that the ISO sensitivity of digital cameras that generally use primary color CCD will not exceed 400. In contrast, complementary color CCD has a Y-yellow color filter, which pays more attention to color resolution, but sacrifices the resolution of some images. On the ISO value, complementary color CCD can tolerate higher sensitivity, which can generally be set above 800.

The third layer: photosensitive layer

The third layer of CCD is the "photosensitive plate", which is mainly responsible for converting the light source of the filtered color layer into an electrical signal and transmitting the signal to the image processing chip to restore the image.

The film size of the traditional camera is 35mm, the diagonal length is 35mm, and the photosensitive area of the 35mm film is 36 x 24mm. When converted into a digital camera, the diagonal length is about 35mm, and the larger the CCD/CMOS size is. In SLR digital cameras, many have CCD/CMOS dimensions close to 35mm. For example, Nikon D 100, CCD/CMOS size area reaches 23.7 x 15.6, which is much larger than consumer digital cameras, while Canon EOS- 1Ds CMOS size is 36 x 24mm, reaching an area of 35mm, so the imaging is relatively good.

There are four kinds of consumer digital cameras in the market: 2/3 inch,11.8 inch, 1/2.7 inch, 1/3.2 inch. The larger the CCD/CMOS size, the larger the photosensitive area and the better the imaging effect. 11.8-inch 3-megapixel camera is usually better than 1/2.7-inch 4-megapixel camera (the light-sensitive area of the latter is only 55% of the former). The increase of CCD/CMOS pixels with the same size is a good thing, but it will also lead to the decrease of the photosensitive area of a single pixel, which may lead to underexposure. However, in order to increase the number of CCD/CMOS pixels while maintaining the existing image quality, it is necessary to increase the total area of CCD/CMOS on the basis of at least maintaining the area of a single pixel. At present, it is difficult to manufacture larger CCD/CMOS, and the cost is very high. Therefore, the larger the CCD/CMOS size, the more expensive the digital camera is. The size of the photosensitive device directly affects the volume and weight of the digital camera. The CCD/CMOS size of ultra-thin and ultra-light digital cameras is generally relatively small. The more professional digital cameras are, the larger the CCD/CMOS size is.

To select a machine, please note the following parameters.

Video technical indicators determine the horizontal definition and color performance of video images. However, when choosing a suitable DV camera, in addition to the consideration of video indicators, the other 50% may depend on simple operation mode, rich interactive interface, professional audio and adaptability to various shooting conditions.

Manual focusing ring

Manual focusing is essential in professional creation, because the current autofocus technology often leads to unforgivable shooting errors such as out-of-focus, inaccurate focusing and inability to focus. Perhaps one day, the accuracy of autofocus will reach 99.9%, and manual focusing still has value. On the lens with professional standard interface, the manual focus ring is needed and the operation mode is completely consistent. In complex shooting, the camera assistant needs to manually mark the focus number with the focus for identification. On cameras with 3 1/3-inch [and below] CCD, the manual focus ring is generally small, and most of them have no digital recognition. However, with the improvement of users' professional requirements in these fields, there are now larger focus rings and digital recognition products.

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On the professional lens with standard interface, zoom has two states: electric servo zoom with variable speed according to finger pressure and manual free zoom. On the non-standard interface lens, the operation mode is defined by each manufacturer. But the common practice is to combine the electric servo with the manual zoom ring in the 3-piece 1/3-inch CCD series. The popular trend is that the electric servo state is divided into fast, medium and slow three speeds according to the zoom speed range, which is convenient for shooting needs in different occasions. However, in this series, only a few models provide digital recognition of focal length.

In CCD series below 1/3 inch, only electric servo zoom is generally set. Because of the size limitation, most models have to change the front and rear seesaw finger pressure keys to up and down zoom keys, which further increases the difficulty of zoom and zoom speed control.

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The manual aperture adjustment ring of professional lens with standard interface is on the wall of the lens barrel, while cameras with 3 1/3 inch [and below] CCD all have manual aperture function, but all of them are set in a certain position of the fuselage without exception, and all of them are operated by a round dial wheel. Some models have multiple functions integrated with one dial wheel and must be switched with other operations, which is not particularly convenient in an emergency shooting state. So try to choose products with single aperture function, which is convenient for manual adjustment of aperture when shooting on site.

Image stabilizer

Hand-held portable DV camera will inevitably cause image jitter, especially at the telephoto end. The image stabilization device can compensate for image shake caused by slight hand shake when shooting with a hand-held camera.

Early DV cameras used digital image stabilizers, or DIS for short. Assuming that the CCD has 680,000 pixels, the camera only takes the middle 340,000 pixels as effective pixels, and the surrounding pixels are used as shock buffers to calculate a clear image. However, if the vibration amplitude is greater than the buffer, the effect is not good, and the original image data will be distorted after calculation.

Nowadays, in the field of professional handheld DV cameras, optical image stabilizer [OIS] has been widely used, and OIS was first used in Canon's camera lens. Its principle is that the gyro sensor inside the machine can monitor the jitter of the hand and send the signal to the linear motor, which can be adjusted to compensate. Because this processing is carried out before CCD image capture, not after circuit processing, OIS device can actually eliminate the influence of hand jitter on clarity and screen angle. Because the processing is carried out in real time at a frequency of several hundred times per second, there is no unnatural residual image or visible interpolation effect.

Neutral gray filter

Under the outdoor conditions with abundant sunshine and high illumination, the incident light of the lens can be reduced to a normal level acceptable to the camera by using the neutral gray filter. In addition, neutral gray filter is needed to adjust the luminous flux when shooting with large aperture and short depth of field. Generally, there are 1/8, 1/64, etc. Of course, the more pieces of neutral gray filter, the wider the adjustable range, the more convenient it is to use.

Sensitivity and minimum illumination

Sensitivity refers to which aperture of the camera is used when the standard illumination is 2000Lux, the color temperature is 3200 K and the gain is 0 dB. The higher the sensitivity, the clearer and more thorough the images taken in the same environment, and the stronger the layering. At present, the highest sensitivity is F 13.0. The high sensitivity of the camera deepens the depth of field and can obtain satisfactory focusing. Even at the fastest shutter speed, it can shoot in a certain light.

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The camera has a video amplifier, which amplifies the CCD signal to a usable level, and its amplification factor is gain. If the aperture and shutter are adjusted to the maximum, the field of view light still cannot meet the minimum requirements of CCD operation, so gain should be used.

The so-called automatic gain [AGC] is to use the automatic gain control [AGC] circuit of the camera to detect the level of the video signal and turn on the gain circuit in time, so that the camera can work in a wide illumination range, that is, the sensitivity of the camera can be automatically improved under low illumination, thereby improving the intensity of the image signal and obtaining a clearer image.

Most shoulder-mounted cameras are equipped with a three-speed gain switch, so the cameraman can choose whether to increase the illumination or turn on the gain switch when the ambient light is insufficient. On most handheld portable machines, there is no such switch. The default setting state of the system is that at the shutter speed of 1/50, when the aperture is still underexposed when it is opened to the maximum, the gain will be automatically turned on. However, the price to pay for turning on the gain and obtaining appropriate picture brightness is inevitable noise. This kind of noise is difficult to detect on the LCD screen of the camera, but once it is played on the TV screen, it will be found that many times the noise has reached an unbearable level, but there is no solution at this time.

So when we use this machine, we must pay attention to the problem of automatic gain. If we don't want to take pictures at the expense of image quality, we'd better pay attention to whether the automatic gain switch in the menu can be turned off.

Image viewfinder

There are three kinds of image finders: high-precision black-and-white CRT image finder, ordinary black-and-white LCD image finder and ordinary color LCD image finder.

Professional and broadcast control machines should use high-precision black and white CRT, that is, kinescope viewfinder, because of its high definition, generally between 500 lines and 700 lines. The price of a high-precision black-and-white CRT viewfinder is the same as that of a standard lens, which may be higher than that of an entry-level 3CCD player.

And now the resolution of color LCD is as high as 400 lines. At present, there is no color LCD viewfinder that can meet the requirements of professional photography.

In addition, the color resolution of human eyes is weaker than the brightness resolution, and black and white images are easier to focus on.

Size is also an important indicator of the viewfinder. The larger size can make the human eye not have to cling to the viewfinder eye mask.

Generally, 1.5 inch black-and-white viewfinder is selected for shoulder loaders; Handheld and portable, no matter in black and white or color, it has not exceeded 0.7 inch.

The zebra print display function design makes it possible to accurately check the image exposure at any time during shooting. If the ambient light is too strong, a zebra pattern can be displayed in the viewfinder to remind you to adjust the aperture and exposure time. According to personal habits, you can choose 100% or 70% ~ 80% zebra stripes.

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The biggest advantage of color LCD screen is that it can rotate 270 degrees, which is very convenient for both high and low angle shooting and tripod selfie. Especially when choosing automatic shooting mode, color LCD screen is an important basis for checking white balance at any time.

time-lapse shooting

Time-lapse shooting is also called interval shooting. For example, in order to record the process of plant growth or flowering, you can shoot a frame every few seconds or minutes, so that you can see the continuous growth or flowering action with the naked eye when playing back. In addition, some models also have a single shot function, which can record the scene for several seconds every time the start/stop key is pressed, and can be used to make animated movies.

Tape compatibility

There are two sizes of DV tapes. What we often see is actually a small tape called MiniDV tape, which usually lasts 60 minutes and the longest is 80 minutes. In addition, a large tape is used, and the longest recorded DV format is 276 minutes.

Handheld machines use MiniDV tapes, while shoulder-mounted machines are generally compatible with both tapes. DVCAM/DV tapes are actually compatible in both directions, that is, DV cameras can use DVCAM tapes, but the recorded tapes are still in DV format. DVCAM cameras can record DVCAM signals with DV tapes and upload them directly to the computer for editing, but they cannot participate in combination or insertion editing on Sony's DVCAM editing video recorder.

audio interface

On the shoulder-mounted machine, professional XLR audio interface with strong anti-interference ability can be used to connect professional microphone or professional mixer. Nowadays, this high-quality audio interface is also adopted by some handheld professional DV cameras.

16: 9/4: 3 exchange

The real 16∶9 camera uses 16∶9 CCD, but the hand-held portable model only uses an electronic deformation stretching technology, because the price of 16∶9 CCD and the complexity of the control circuit decide that it can not be realized at the current price for the time being.

There is an address below. For reference only.