The use of digital cameras

Because the back depth of field of the lens is relatively large, people call the distance that can be clearly imaged after focusing as hyperfocal distance. Fool cameras generally use hyperfocal distance, which makes use of the feature that the scene can be clearly imaged at a certain distance with a short-focus lens, omitting the focusing function. Therefore, generally, low-grade fool cameras can't focus automatically, so they can only use hyperfocal distance. As mentioned earlier, "clarity" is not an absolute concept, and the scenery in hyperfocal distance is not really clearly imaged. Because there is no focus, it must be blurred, but the degree of blur is generally acceptable. This is the reason why the negative film taken by a fool's camera can't be enlarged too much.

Program automatic exposure

Programmable automatic exposure is the product of the combination of electronic technology and artificial intelligence. When exposed in this way, the camera can not only calculate the appropriate exposure according to the light conditions, but also automatically select the appropriate exposure combination.

storage medium

An image storage medium is a device for storing images in a digital camera, which is usually called a memory card. There are three main specifications of memory cards used in digital cameras in the market: smart media: small in size, cheaper than CF, with a maximum capacity of 64MB, which can be used as a switching device for disk adapter cards, card readers or PCMCIA. COMPACTFLASH: It is more expensive, thicker than SM card, with larger capacity, up to 128MB, and faster. The switching devices are card readers and PCMCIA. Memory stick: At present, it is a special memory specification for Sony and can only be used on Sony machines.

SLR camera

Single lens reflex (SLR) refers to single lens reflex. In this system, the unique design of the mirror and prism enables the photographer to directly observe the image passing through the lens from the viewfinder. It can be seen from the structural diagram of a single-lens reflex camera that the light passes through the lens and reaches the reflector, and then refracts to the focusing screen above to form an image. Through the eyepiece and pentaprism, we can see the scenery outside in the observation window. When shooting, press the shutter button, the reflector will pop up, and the shutter curtain in front of the film will be opened at the same time. The light (image) passing through the lens will be projected on the film to make the film sensitive, and then the reflector will immediately return to its original state, and the image can be seen in the viewfinder. This structure of the single-lens reflex camera ensures that it is shot through the lens, so that the image seen in the observation window is always consistent with the image on the film, and its framing range is basically consistent with the actual shooting range, eliminating the parallax phenomenon of the paraxial head-up framing camera. From the perspective of learning photography, it is very conducive to intuitive framing and composition. Another major feature of a single-lens reflex camera is that it can replace lenses with different specifications.

electronic viewfinder

Electronic viewfinder (EVF), the field of view ratio of electronic viewfinder is much larger than that of optical viewfinder. For example, the EVF of Sony DSC-F707 has a field of view ratio of 99%. Electronic viewfinder is also more practical, not only cheaper, but also more energy-saving when used, and can be used in any ambient light. Although the viewing angle and color effect in the viewfinder are not exactly the same as the final effect, they will adapt quickly after being used for a period of time.

Fixed focus camera

A camera with a fixed focal length lens. Generally speaking, the "fool" camera with fixed focus lens is smaller and has better imaging quality than the zoom "fool" camera with the same price. Consumers who choose this camera often look for its compact size and excellent lens quality.

contrast

Contrast is a measure of the different brightness levels between the brightest white and the darkest black in an image. The larger the difference range, the greater the contrast. The smaller the difference range, the smaller the contrast. The good contrast ratio of 120: 1 can easily display vivid and rich colors. When the contrast ratio is as high as 300: 1, all levels of colors can be supported. However, contrast and brightness face the same dilemma. At present, there is no effective and fair standard to measure contrast, so the best way to identify it depends on the eyes of users.

Multiple measurement mode

It is equipped with three metering modes: fixed-point metering, central offset metering and multiple metering modes to meet different shooting conditions and uses. Multi-metering mode divides the image into 49 areas, and metering each area, so that the photographed image can get a balanced exposure.

Red-eye prevention function

It refers to the phenomenon that the photographer's eyes appear red spots because of the reflection of the blood vessels in the fundus of the subject when shooting a portrait with a flash. But now most mainstream digital cameras have red-eye prevention function, but if they are not turned on, they still won't work.

Handshake function

There are two functions of digital camera to prevent hand shock: one is optical and the other is digital. Optical hand shock prevention is the same as traditional camera. The lens designed by the special envoy is arranged in the imaging optical path, which can sense the vibration of the camera and automatically adjust the optical path according to the characteristics and degree of vibration to make the imaging stable. Digital hand shock prevention is a software calculation method, which uses the interaction between imaging scanning process and mechanical shutter opening process to correct the influence of vibration and obtain a stable picture. Generally speaking, a well-designed optical anti-hand shock system is more reliable and more realistic.

resolution ratio

A parameter used to measure the amount of data in a bitmap image. Usually expressed in ppi (pixels per inch). The more data it contains, the longer the graphic file and the richer the details. But larger files also need to consume more computer resources, more RAM, more hard disk space and so on. On the other hand, if the image contains insufficient data (the graphic resolution is low), it will appear rather rough, especially when the image is enlarged to a larger size. Therefore, in the process of image creation, we must decide the correct resolution according to the final use of the image. The trick here is to ensure that the image contains enough data to meet the needs of the final output. At the same time, it should be moderate and occupy computer resources as little as possible.

"Resolution" is generally expressed by the number of pixels in all directions, such as 640X480. In some cases, it can also be expressed as "pixels per inch" (ppi) and the length and width of the graph. Such as 72ppi and 8X6 inches.

Ppi and dpi (dots per inch) are often mixed. Technically, "pixel" (P) only exists in the field of computer display, and "dot" (D) only appears in the field of printing or printing. Please pay attention to the distinction.

speed

Sensitivity, adjust the sensitivity of the camera according to the different intensity of the light source.

When using traditional cameras, we can choose negatives with different sensitivities (speeds) according to the brightness of the shooting environment. For example, ISO200 can be used in cloudy environment, and ISO400 or higher can be used in concert environment. Digital cameras have a similar function, which changes the ISO value by changing the amplification factor of the signal amplifier in the photosensitive chip. However, when the ISO value increases, the amplifier will also amplify the noise in the signal and produce a coarse-grained image.

hole

Aperture is a device used to control the amount of light entering the photosensitive surface of the fuselage through the lens, usually in the lens. We use the f value to represent the aperture size.

Aperture f value = lens focal length/lens aperture diameter

As can be seen from the above formula, to achieve the same aperture f value, the aperture of a long focal length lens is larger than that of a short focal length lens. The complete series of aperture values is as follows:

F 1，F 1 .4，F2，F2 .8，F4，F5 .6、F8，F 1 1，F 16，F22，F32，F44，F64

It is worth mentioning here that the smaller the f value of the aperture, the more light enters in the same unit time, and the light entering amount of the upper level is exactly twice that of the lower level. For example, if the aperture is adjusted from F8 to F5.6, the amount of light entering will double. We also said that the aperture should be opened one level. For consumer digital cameras, the aperture f value is often between F2.8-F 16. In addition, many digital cameras can adjust the aperture by 1/3.

Aperture and shutter take precedence.

In addition to providing automatic mode, advanced digital cameras usually have two options: aperture priority and shutter priority, so that you can decide a certain aperture value or a certain shutter value on some occasions, and then match the appropriate shutter or aperture respectively to present different depth of field (sharpness) or effects.

Aperture priority exposure mode

After we decide the aperture f value ourselves, the camera metering system will automatically choose the appropriate shutter speed (which can be an accurate stepless shutter speed) according to the light conditions at that time. A digital camera with an exposure mode dial usually engraves the letter "A" on the dial to indicate the aperture priority mode (see Figure 4). Aperture prerequisite mode is suitable for photography that emphasizes the depth of field effect.

Because the focal length of digital camera is much shorter than that of traditional camera and the aperture of lens is small, it is difficult to produce narrow depth of field. Some digital cameras have a special portrait exposure mode, using built-in programs to blur the foreground and background.

optical zoom

Zooming is realized by optical lens structure. The zoom mode is similar to that of a 35mm camera, that is, the scene to be shot is enlarged and reduced by the lens movement of the camera. The larger the optical zoom factor, the farther the scene can be shot. At present, the optical zoom magnification of digital cameras is mostly between 2 and 5 times, and the optical zoom effect of some code cameras reaches 10 times. The optical zoom factor of home camcorder is 10 ~22 times, and it can clearly shoot things 70 meters away. Using a magnifying glass can increase the optical zoom factor of the camera.

optical viewfinder

The components commonly used in traditional mass cameras to view through a set of lenses that have nothing to do with the shooting lens (often linked with the zoom lens on high-end stupid machines) have low cost, but they have parallax, and what they see is not entirely taken by themselves.

wide-angle lens

That is, wide angle, also known as short lens. Because the focal length of the wide-angle lens is very short, the scene projected on the basement membrane becomes smaller and the shooting angle of the lens becomes wider. Wide-angle images can not only shoot more scenes, but also shoot in narrow environments.

Bloody eyes

"Red eye" refers to the phenomenon that the pupil of the human eye appears red spots in the photo when the digital camera takes a close-up portrait in flash mode. It can be understood that in a dark environment, the pupil of the human eye will be enlarged. At this time, if the optical axis of the flash is close to the optical axis of the camera lens, the intense flash light will be reflected into the lens through the human fundus, which is rich in capillaries. These blood vessels are red, so they form erythema. Red-eye prevention is a function of the flash, which is to flash once before the official flash to narrow the pupil of the human eye, thus reducing the phenomenon of red eye.

Ring lamp

Ring flash is a kind of lamp directly installed on the camera lens, and the light-emitting tube is ring-shaped. Low power, equipped with effect light. The light is even and there is no shadow. It is very suitable for macro photography and very useful in the fields of medicine and scientific research. In close-range and macro photography, because the subject is very close to the lens, ordinary flash will produce heavy shadows, and the exposure is difficult to control. Ring flash is often used at this time.

focal distance

If you have seen "f =" in the English manual of the camera, then the number behind it is usually its focal length, that is, the focal length. For example, "f=8-24mm, 38- 1 15 mm (equivalent to 35mm)" means that the focal length of this camera is 8-24mm, and the diagonal viewing angle is equivalent to 38- 1 15mm of the traditional 35mm camera. Generally speaking, the standard lens focal length of a 35mm camera is about 28-70mm, so if the focal length is higher than 70mm, it means that the telescopic effect is supported. If it is less than 28mm, it means that it has wide-angle shooting ability.

"Focal range" is the extension of focal length, which is usually divided into general shooting distance and close-up distance. The general shooting distance of a camera is usually marked as "from a certain centimeter to infinity", and products designed by advanced technology often provide close-range shooting function (macro) to make up for the problem of not focusing in general shooting mode. Some cameras emphasize the magical ability of supporting 1 cm close-up, which is suitable for shooting fine objects.

depth of field

When shooting, the process of adjusting the camera lens to make the scene at a certain distance from the camera clearly image is called focusing, and the point where the scene is located is called focus. Because "clarity" is not an absolute concept, the scene imaging before focusing (close to the camera) and after focusing can be clear. The sum of the front and back ranges is called the depth of field, which means that as long as the scene is within this range, it can be clear. The depth of field is first related to the focal length of the lens. The lens with long focal length has small depth of field, while the lens with short focal length has large depth of field. Secondly, the depth of field is related to the aperture. The smaller the aperture (the larger the numerical value, for example, the aperture of f 16 is smaller than f 1 1), the greater the depth of field. The larger the aperture (the smaller the value, for example, the aperture of f2.8 is larger than that of f5.6), the smaller the depth of field. Secondly, the depth of field in the foreground is smaller than that in the back, that is to say, after precise focusing, the scene in front of the focus can be clearly imaged, while the scene in the back of the focus is clear.

Inter-mirror focal plane shutter

The inter-mirror shutter consists of a series of thin steel sheets, which are placed between lens units. The shutter release button triggers a spring to open the blade during exposure and then close it. This type of shutter is also called blade shutter. The focal plane shutter is located in front of the film in the camera. It is named because it is in front of the focal plane, that is, the film position. Comparatively speaking, the focal plane shutter has the following two advantages: First, because the focal plane shutter is installed in the camera body instead of the lens, such interchangeable lenses are often not too expensive. But for the blade shutter, the shutter is a part of the lens, so the lens containing the blade shutter will be more expensive. Secondly, the focal plane shutter can have a faster exposure speed. In order to understand the reason, it is necessary to understand the working principle of focal plane shutter, which operates a bit like a roller shutter. First, pull up the first curtain, open the shutter and let the light shine on the film. Then, when the predetermined exposure ends, the second sub-curtain moves together with the first sub-curtain and blocks the light. This is the reason why there is an upper limit to the speed of the curtain passing through the film when the focal plane shutter works.

MTF of lens

MTF of a lens is a test parameter that reflects the imaging quality of the lens and the ability of the lens to reproduce the real world. The full name of MTF in English is modular transfer function. Although MTF of lens has been adopted by several lens manufacturers, it is not an international standard. Because digital cameras are the product of photoelectric integration, especially non-professional models, lenses are irreplaceable. Imaging not only reflects the imaging performance of the lens, but MTF is only one of the parameters reflecting the imaging quality of the lens.

battery of lens

The lens of a digital camera consists of multiple lenses, and the materials are divided into two categories: glass and plastic. Some manufacturers emphasize that their camera lens is made of glass, so it has good transparency and the projected image is clearer. However, at present, many test reports show that glass lenses do not necessarily bring clearer images than plastic materials, and at the same time, glass lenses may increase the weight of the camera, so you should observe in many aspects when purchasing, and don't stick to the lens materials.

drill

Lens thread, the diameter of the front end of the camera lens.

shutter

It is a device that prevents light from reaching the front of the camera. Generally speaking, the larger the shutter time range, the better. Low seconds is suitable for shooting moving objects, so a camera emphasizes that the shutter can reach116000 seconds at the earliest, which can easily capture fast moving targets. However, when shooting traffic at night, the shutter time will be lengthened, and the silky water flow effect in ordinary photos can only be photographed with a slow shutter.

As for the common B shutter function of monocular cameras, although you can freely decide the exposure time and have high shooting flexibility, most consumer digital cameras can't support it at present, and can provide the default values of slower speeds such as 2 seconds, 8 seconds, 16 seconds at most.

Shutter delay time

When the camera does not use the focus lock function and ensures that it is in the auto-focus working state, the time from pressing the shutter release button to starting exposure is called shutter lag time.

Shutter pre-exposure mode

After we decide the shutter speed ourselves, the camera metering system will automatically select the appropriate aperture F value (which can be a stepless F value) according to the light conditions at that time. A digital camera with an exposure mode dial usually engraves an "S" letter on the dial to indicate the shutter prerequisite mode. Shutter priority mode is suitable for photography that needs to control the shutter. High-speed shutter can condense action, and slow shutter can turn moving vehicles into light beams.