Frequently asked questions about digital cameras

Q: Ordinary fool cameras generally have the function of automatically printing the shooting date or time. Why can't my digital camera print the date on the photo when shooting? How can we make up for it?

A: Most digital cameras don't support adding dates directly to photos. This is mainly because digital photos all support Exif information format, which contains parameters automatically generated by the camera, such as shooting date, time, aperture, shutter speed and so on. If you need to view it, you can use the picture viewing software that supports reading Exif information, which is clear at a glance. However, some brands of digital cameras support adding dates directly to the photos taken. You can choose from the function menu as needed. Although adding date words may destroy the artistry of the whole photo, I think.

Giving users the right to choose is a better design. In fact, it is very simple to add a text description such as shooting date to digital photos. We can use related software and solve it through post-processing. For example, "PhotoCap" is a famous post-processing software for digital photos, which can easily add words such as date to digital photos.

Q: Most digital cameras use charge-coupled devices (CCD) as image sensors, and now some products have begun to use CMOS sensors. What are the main characteristics of CMOS sensors?

A: First of all, CCD image sensor depends on special processing technology, which makes its manufacturing technology fine and expensive. CMOS sensors are processed by integrated circuits produced by most semiconductor manufacturers, so the overall cost of the system using CMOS chips will be very low. Other functions can be integrated on CMOS chip, such as analog-to-digital conversion, load signal processing, white balance processing, camera control, etc., which further reduces the cost of the whole machine. Secondly, CMOS only needs to use one power supply when working, compared with CCD. However, there is still a big problem in the practical stage of CMOS sensor: ordinary products are easily affected by noise, and the imaging quality is quite different from CCD. However, Canon uses a special large-size CMOS sensor in digital SLR products, and the imaging quality is even better than that of ordinary CCD.

Q: I am a digital photography enthusiast. I bought a digital camera some time ago. I'd like you to briefly introduce the basic structure of a digital camera.

A: A digital camera is mainly composed of the following parts: First, a CCD image sensor, which is equivalent to the photosensitive film of a traditional camera. Another important component is the special DSP for image processing, such as the image processing chip DIGIC used in Canon digital camera, which is used for image compression, conversion, filtering and correction, and is the "brain" of the camera. In addition, there are other special controllers to manage camera operation, read and write memory cards, and manage file systems. There is also an EPROM chip, which stores the firmware of the camera, which is equivalent to the BIOS chip of the computer motherboard, or the operating system of the whole camera, and can usually be upgraded. As for the fuselage and lens components, including autofocus system and shutter control system, there is little difference from traditional cameras.

Q: I am a beginner in digital photography. Although I used the highest resolution setting, the photos I took were still a little blurred. And the photos taken often have many small spots. What is the reason?

A: Whether the photos are clear or not is not directly related to the resolution you set when shooting. In many cases, the picture will be blurred. For example, when the light is poor, camera shake will lead to blurred images. You can increase the shutter speed as much as possible by increasing the aperture and ISO settings. It is best to use a tripod when taking pictures, or put the camera on a fixed object such as a table, and use a flash when necessary. Improper focus mode or focus selection is also an important reason for blurring the picture. In addition, a dirty lens will blur the image taken by the camera. Please use special lens cleaning paper to clean the lens. As for the small spots (noise) on the picture, it is usually caused by too dark light or too high sensitivity setting, which is a problem that ordinary digital cameras can't overcome. Noise is usually caused by "electrode dark current" in CCD module. Dark current refers to the amount of charge that CCD still has without incident light. Dark current should be zero in theory, but it can't be realized in practice, and its intensity will increase with the increase of temperature (the noise number may increase by 1 times for every increase of 10℃).

Q: I bought a digital camera last year, and it often fails to turn on or turn off automatically during use. What happened?

A: There are many possible reasons. Troubleshooting the camera itself is usually due to power problems. If the digital camera suddenly shuts down automatically during use, the first thing you should think of is that the battery is low. Digital camera is a big power consumer, and it is often turned off because of insufficient battery power. If the digital camera still can't be turned on after replacing the battery, and you find that the camera is hot, it is because the camera has been used continuously for too long, resulting in overheating and automatic shutdown. For users in the north, because the outdoor temperature is too low in winter, the battery often fails and cannot be turned on. In addition, the memory card is damaged or installed abnormally, which may also lead to the camera not being used normally. You can format the memory card first. In addition, we should pay attention to the write protection of SM, SD and other memory cards.

Q: I often find that the colors of the scenes in digital photos and those seen by my eyes have changed, sometimes red, sometimes yellow. Especially photos taken indoors and at night often have serious color cast. Why?

A: This is mainly because the white balance is not adjusted properly. The white balance adjustment function of a digital camera is similar to that of a traditional camera with a color temperature filter, with the purpose of achieving accurate color reproduction, except that the color temperature of a digital camera is adjusted by a circuit, and the mixing ratio of the three primary colors of red, green and blue is changed by an electronic circuit, thus correcting excessive color components in light. Usually, the automatic white balance function of digital camera can ensure the accuracy of color reproduction, but it is difficult to shoot under some complicated conditions. We can use the camera's custom white balance function to make precise adjustment. In this mode, you aim the camera at the white object in the shooting scene, and then press the shutter halfway. At this time, the camera will automatically record the white state in this light. According to this value, the color can be restored correctly in the next shooting.

Q: The digital photos I take often appear on the bright side or the dark side. Why do digital cameras have metering errors? How to make up for it?

Answer: The automatic metering of digital cameras is measured according to the "standard gray scale", that is, it is assumed that the reflectivity of the metering area is 18%, and then the values of the aperture and shutter are determined by metering according to this ratio. The source of the value of 18% depends on the reflective performance of intermediate tones in natural scenery. If there are many white tones in the framing picture, if you shoot according to the aperture shutter value measured by the camera's automatic photometry, the shot will be underexposed, and the white background will look gray. Therefore, it is necessary to increase the exposure compensation value of the camera when shooting scenes with reflectivity greater than 18%. On the other hand, if you shoot a scene with a reflectivity lower than 18%, such as a black background, the shot photos will often be overexposed, and the black background will turn gray, so the reflectivity is lower than 18. Simply put, it is "white plus black minus". Although the exposure of digital pictures can be adjusted by digital darkroom processing in the later stage, for overexposed pictures, the details and levels of dark parts have all been lost, and it is difficult to adjust them back. However, if the photo is seriously underexposed, there will be more noise and some details will be lost after the correction exposure, so try to make the photo have the correct exposure.

Q: The computer can only display 24-bit full-color JPEG files. That is to say, a digital camera can meet the needs as long as it is equipped with an 8-bit A/D converter, but why use a converter above 10BIT?

A: There are several reasons. First, high-end digital cameras usually use RAW format to save the photos taken. RAW can completely record all the original data when shooting, get rid of the constraints of JPEG specification, and make the color and image quality perfect. The second is to add reference data in the calculation of merged digital images. Some DSP programs of digital cameras have the function of improving resolution. This program mainly refers to the performance of neighboring pixels of sampled pixels and makes statistics. Therefore, the higher the bit, the more sampling parameters of the A/D converter, and the better the performance of the 24-bit JPEG file calculated by merging. Therefore, every red, green and blue output of a digital camera should at least reach 10BIT (1024 gray scale). At present, most of them are equipped with 12-bit A/D processors. Individual high-end products have reached 14BIT.

Q: What are the methods to improve the sensitivity of CCDISO? In addition, is the exposure latitude of CCD much worse than that of traditional film?

Answer: A digital camera using a fixed CCD as a photosensitive element cannot choose a negative to replace a negative with a higher or lower photosensitive capacity like a traditional camera. There are usually two ways to improve the ISO capability of CCD. One is to simplify the pixel signal of CCD in a specific area and improve ISO. Because CCD can't increase the photosensitive area physically, the joint matrix is used to simulate the large photosensitive area, so the higher the ISO, the lower the resolution. Another method is to obtain reasonable exposure performance according to data operation through a specific signal enhancement circuit, but it is usually accompanied by noise. Therefore, the maximum ISO value of a digital camera mainly depends on the highest acceptable signal-to-noise ratio (S/N). In the case of accurate exposure, CCD will capture a wider range of image tones than traditional film. An ordinary CCD can record the Gao Fancha scene around 250: 1 (8-level aperture). The high-grade FFCCD system can handle the color range of near 1000: 1. But the final image output on photographic paper can only reproduce the tone range of 32: 1 or 5-level aperture.

Q: I'm going to buy a digital camera, which is mainly used for landscape shooting. Is the 10X large zoom product on the market suitable? How to determine the rationality of digital camera focal length?

A: The telephoto digital camera does have many unique advantages, such as shooting distant objects and taking close-up photos with blurred backgrounds. But for shooting scenery, wide angle is the most commonly used. Recording the dribs and drabs of daily life, wide angle can also be better qualified for this job. At present, the wide-angle focal length of telephoto cameras on the market is usually around 38mm, which is unreasonable for ordinary family users and users who like landscape photography. So starting from your needs, I suggest you choose a digital camera with a wide-angle lens. The wide-angle end of the camera should be at least below 28 mm. Now there are many products that meet the requirements on the market, and even some products have a wide-angle end of 24mm, which is very suitable for landscape photography.

Q: Why do ordinary digital cameras have more focal points? You can even choose the focus freely. What are the benefits of being more focused?

A: For SLR cameras, more focus and focus options mean high prices. This is determined by the structure of SLR camera, and its focusing components are separated. In order to ensure high-speed focusing, the optional focusing range and position are very limited. The focusing mode of ordinary digital camera is to detect the imaging of the designated area on CCD, and complete autofocus through phase analysis. Therefore, in theory, any position and any size area of CCD can be analyzed and focused separately, so there are not a few products that focus above 5 o'clock, and some products can even choose the focus freely. For example, almost all products of Canon2002 after 2002 also have AiAF capability, that is, they can move the focus freely in most areas in the center of the screen. In order to pursue flexible creativity, photographers often don't stick to putting the subject in the center of the picture to make a composition, and they can choose the focus freely, which will bring great convenience to all kinds of innovative composition. No matter where the subject is, they can move the focus and concentrate on composition without being distracted by the focus.

Q: I am a digital photography enthusiast and often go out to shoot for a long time. I am going to buy a "digital companion" to store my photos. How should I choose?

A: At present, there are many kinds of "digital camera companion" products on the market, most of which can only be used to store photos, but some products have begun to provide color LCD screens and more functions, and some products are no longer digital camera companions in a simple sense, but can also be used to listen to music, watch movies and play games.

Simple "digital camera companion" is destined to be a transitional product. I suggest you buy multifunctional products, but these products are usually more expensive, so you can also consider buying second-hand pocket laptops. In fact, the price of memory cards has dropped a lot now. Two CF cards or SD cards with 1GB cost only 1,000 yuan, and can store thousands of photos, which can fully meet the general shooting needs. The role of "digital camera companion" is not very big.

Q: Many professional digital cameras now offer the option of saving photos in RAW format. What are the characteristics of RAW format?

K: In the past digital cameras, TIFF and JPEG were mostly used for image storage. Although the former can save image information lossless, its coding method is quite special, and the file size is quite huge, occupying a lot of space. The latter is compressed, which reduces the file size and sacrifices some image information. In the RAW file storage mode, the original information from the image sensor is recorded without any white balance, gamma correction and dynamic adjustment. It not only leaves a very rich space for post-image processing, but also has a small file size. This technology was quickly recognized and applied by the market. Some products also adopt the new technology of embedding JPEG files in RAW files. Users can save two types of files at the same time by pressing the shutter once. At present, RAW has become an open format. Not only digital camera manufacturers provide users with processing and conversion programs for RAW files, but also mainstream image processing software such as PhotoShop has related plug-ins to process RAW files.

Q: I'm going to buy a digital camera before May Day. What should I pay attention to when buying a digital camera?

Answer: First of all, look at whether the package is old and there are no signs of opening it. If there are obvious signs of opening, it is likely that you chose this machine and then look at the appearance. Look for scratches, including lens, LCD, EVF and casing, and check whether the accessories are complete. Then you can take a short shot and take a closer look at the LCD and EVF. As for the bad spots on the CCD, you should be more careful. Because it is difficult to see if there is any bad point in CCD directly on DC, it is necessary to import the picture into PC and watch it again. Due to the problems in the manufacturing process of CCD, some defects often occur, which are manifested as that a certain image point is not bright or always bright. The bad point of CCD can be tested by software, and the famous one is "dead pixel". In addition, the physical aperture of the lens must also be considered. Large-aperture, multi-lens and multi-group high-quality lenses, including aspheric lens, ED lens and multi-layer coating, are important configurations of high-end digital cameras.

Q: Digital cameras are becoming more and more popular now. What are the characteristics of digital camera lens compared with traditional cameras? How to protect it?

A: First of all, ordinary digital cameras require higher resolution because the imaging device is much smaller than film. For example, for a certain subject, horizontal 100 pixel is needed to perfectly reproduce its details. If the imaging width is 65,438+00 mm and the optical resolution is 65,438+00 lines /mm, a lens is enough. If the imaging width is 65,438+0 mm, the optical resolution of the lens must be above 65,438+000 lines/mm. In addition, because CCD is sensitive to infrared rays, it is necessary to add a special infrared filter behind the lens, and the coating method of the lens is different. The camera lens is fragile, so you must be careful. If there is only a little dust, it is recommended not to wipe it, which usually will not affect the imaging. If there are fingerprints, it is recommended to blow off the dust with a balloon first, and then gently wipe it with a lens pen. If the camera is not used for a long time, it is best to put it in a moisture-proof sealed container to avoid the lens from mildew.

Q: The edges of some digital photos I take are often distorted. What is the distortion of digital camera lens? How to avoid distortion as much as possible when shooting?

Answer: All optical camera lenses have the problem of distortion, which belongs to the geometric distortion of imaging. It is a picture distortion phenomenon caused by different image magnifications in different areas on the focal plane. The degree of this distortion increases from the center of the picture to the edge of the picture, which is mainly reflected in the edge of the picture. The distortion of zoom lens is particularly serious. Generally, when shooting at the wide-angle end, the edge of the picture often protrudes outward, which is called barrel distortion. When shooting with telephoto end, the edge of the picture often sinks inward, which is called pincushion distortion. Distortion will lead to image distortion during imaging. In most cases, slight distortion will not have much impact on the image quality, but some applications may be sensitive to distortion, such as reproducing data and shooting regular objects such as buildings. And I hope the distortion is not too serious, otherwise the geometric features of the subject will be obviously distorted. In order to reduce distortion, try to avoid using the widest angle end or the farthest lens focal length when shooting, and use a smaller aperture. Besides distortion, there may be other "aberrations" in the camera lens. The so-called "aberration" means that when light passes through the lens of a digital camera to image on the focal plane, it will produce various distortions, which will lead to various deviations in the focused image. There are many kinds of aberrations, including distortion, spherical aberration, astigmatism, coma, field curvature and chromatic aberration, which will affect the imaging quality in different ways.