Ask some basic knowledge about SLR cameras, how to choose SLR cameras and matters needing attention, and the advantages and disadvantages of D300 50D.

How to buy a SLR camera; How to buy a digital camera; Matters needing attention in choosing a digital camera How to choose a digital camera?

Digital camera has entered the field of mass consumption. Many friends want to own a digital camera, but they don't know how to choose. As a digital product with high technical integration, there will be a problem of how to choose it in the purchase process. Now everyone pays great attention to the number of pixels of CCD when buying digital cameras. In addition to resolution, other performance indicators of digital cameras are more worthy of consumers' attention. I will tell you how to choose the "best digital camera" with real price and practical function from different angles.

First, understand the camera.

1. pixels and resolution pixels are the most HyPic units of digital images, and each pixel is a small point. When pixels of different colors are gathered together, it becomes a moving photo. Digital cameras often use pixels as the basis for classification, but many people think that the number of pixels is the number of photosensitive points on the CCD photosensitive unit. In fact, this statement is not entirely correct. At present, many manufacturers can produce higher resolution under the CCD photosensitive unit with the same photosensitive point through special technology. What is the relationship between pixels and resolution? How to interpret these two figures when purchasing?

★ The higher the picture resolution, the more pixels are needed. For example, a picture with a resolution of 640×480 needs about 3 10000 pixels, and a picture with a resolution of 2084× 1536 needs at most 3 14000 pixels.

★ The resolution can have multiple values. The more resolution the camera provides, the more flexibility you have in taking and saving photos.

★ The resolution of the picture is related to the imaging size and magnification at the time of output. The higher the resolution, the larger the imaging size and the higher the magnification.

Total number of pixels refers to the total number of pixels contained in CCD. However, due to the lack of light at the edge of CCD, some of them do not need to be photographed. Subtracting this part of pixels from the total number of pixels is the effective number of pixels. Therefore, when reading the product manual, remember to pay attention to the effective number of pixels that can be used in actual shooting, not the total number of pixels.

2. The quality of the lens and shutter lens directly affects the quality of the camera. Under normal circumstances, manufacturers with deep background in traditional cameras will have better lenses in their digital cameras.

★ Focal length Due to the special lens specifications of digital cameras, it is impossible to predict the range of scenes that can be shot from this data. Most manufacturers will increase the focal length of 35mm traditional cameras after the lens focal length parameters. If it is a souvenir or a photo of life, you only need to buy the fixed-focus lens model. If there are diversified needs, a camera with three times or more optical zoom capability will be more suitable. Focal length, also called focal length, usually refers to the distance from the center point on the lens axis to when the image can be clearly imaged. In a camera, it refers to the focal length of the whole lens group in mm (millimeter). The longer the focal length, the narrower the angle of the visual range of the lens, but it has the effect of magnification and proximity, just like the lens of a telescope; The shorter the focal length, the larger the shooting range and the smaller the relative object, which is suitable for shooting large scenes at close range, which is what we often call a wide-angle lens. For digital cameras, the longer the focal length, the longer the depth of the lens group. In addition, data such as f=5.5mm or 5.5mm can be found from the camera lens. However, because the focal length of the lens of a digital camera is generally much shorter than that of an ordinary 35mm camera, manufacturers often indicate something similar in the manual: a 36mm lens is equivalent to a 35 mm camera for users to compare.

★ Aperture range The larger the aperture, the more you can adapt to the lack of light. If there are more than two aperture values, the application flexibility of the camera will be greater. Aperture is one of the important mechanisms that affect exposure. It usually refers to the control device composed of about 5 to 9 pieces of metal in the lens group, which can form circles with different sizes to control the amount of light entering the lens. The larger the aperture, the more light per unit time. The size of the aperture is expressed by numbers. The larger the number, the smaller the aperture, that is, the less light enters. All the marks on the lens refer to the maximum aperture of the lens, that is, the value in the fully open state, such as 1: 3.2, but on the zoom lens, you will see the marks of 9.2-28mm 1: 2.8-F3.9, indicating that the maximum aperture is F2.8 when the focal length is 9.2mm and the maximum aperture when the focal length is 28mm.

★ Shutter The shutter of a digital camera can support 2 ~11000 seconds, which can meet the general requirements. Of course, if there is a wider shutter range, it can better meet all kinds of strict shooting conditions, such as shooting high-speed moving objects or starry nights. The shutter is used to adjust the exposure time of the camera. The unit is seconds, expressed in reciprocal. For example, 30 and 250 represent 1/30 seconds and 1/250 seconds respectively, so the smaller the number, the slower the shutter speed. The faster the shutter speed, the easier it is to capture high-speed moving images. Generally, it is not easy to blur the image due to jitter when shooting, but high speed may lead to insufficient light input. Usually, when the light is strong, you must use a high-speed shutter or increase the aperture. When the light is insufficient, a slow shutter is more suitable, but a tripod may be needed for assistance.

3. Macro shooting Macro is to zoom in and out the subject to be shot. The point is to shoot tiny objects to the size you want. In macro mode, various digital cameras have different abilities, and some can even close to 0. 1 cm for close-up.

4. Other functions, such as red-eye flashing, white balance and exposure compensation, will have greater flexibility for shooting in various environments.

★ Automatic white balance correction The photosensitive part of a digital camera is equivalent to the negative of a traditional camera. The photosensitive element of a digital camera is fixed, so it is necessary to reflect the change of light source with the help of white balance correction ability. It is mainly designed for photosensitivity in different environments. Different light sources will produce different degrees of chromatic aberration, which may make the color blue and yellow, and the white balance correction can be corrected.

★ Exposure compensation Because the camera's automatic exposure function is based on the light entering amount of medium gray reflected light, if there is too much white (reflected light) in the shooting picture, the light entering amount will be higher than the photometric standard value, thus misleading the camera to think that the light is very strong and the aperture is reduced, resulting in underexposure of the photo and the white part becoming not white enough. Exposure compensation is aimed at this situation. Only when the exposure is increased by 1 or 2 frames can a bright and correct image be obtained. On the other hand, in most cases of black, it is necessary to reduce the exposure of 1 or 2 squares.

Many consumers, because they don't understand digital cameras, unilaterally think that pixels are high. Not exactly. When choosing a digital camera, we should consider its digital and optical characteristics.

1, digital camera lens. A well-designed high-end camera lens consists of multiple groups of lenses, including aspherical lenses, which can significantly reduce color shift and minimize graphic distortion and distortion. Expensive fluorite or glass is used as a lens. In order to reduce weight and cost, the lenses of household and semi-professional cameras are made of resin.

2. Image value of CCD of digital camera. CCD is the heart of digital camera, and it is also one of the main factors that affect the manufacturing cost of digital camera. Therefore, it has become an important standard for digital camera classification. At present, entry-level products are all 3-5 million pixels, and commercial and semi-professional users prefer products with more than 5-/kloc-0.0 million pixels.

3. Zoom of digital camera. Optical zoom is a real zoom, which will not affect the imaging quality of photos; Digital zoom is electronic zoom, which is a local enlargement at the expense of photo clarity.

4. Battery and power consumption of digital camera. Digital cameras have LCD screens and built-in flashlights, so the battery consumption is higher than that of traditional cameras. It's cheap to use the No.5 battery, and you can buy it anytime and anywhere, but it won't take long for the battery to die. Therefore, it is best to choose the model equipped with rechargeable lithium battery. At present, mainstream digital products have been designed as lithium batteries, and complete charging equipment is provided as accessories.

5. Additional functions. The more functions, the more fun and uses it means to use a digital camera. For example, many digital cameras have video output function, which can be connected to TV to browse photos; Some can set their own startup screen and shutter sound like mobile phones; Some can have short-term digital video recording function. The driver installation of digital camera should be very simple, and it should be able to download pictures quickly and preview them. For example, the software function attached to Canon digital camera is perfect, which can classify and manage pictures, and the settings when printing are more diverse, and pictures can also be simply modified.

Image sensor is the decisive factor of camera performance. Generally speaking, the pixel value of the image sensor should be greater than the maximum pixel value of the real shot image. In order to make up for the pixel shortage of image sensors, some manufacturers use software interpolation to improve the pixel value of images. In fact, this interpolation method can be realized in almost all image processing software, so it is of little practical significance. The purchase must be based on the hardware pixel value of the image sensor, not the maximum pixel value of the output image.

Digital cameras record photo information in a semiconductor element called CCD (Charge Coupled Device), instead of the film of a silver salt camera. The size of CCD, like TV, refers to the diagonal length, expressed in inches, such as "1.27 inch (note)". The larger the CCD, the more pixels and the higher the sensitivity. Therefore, with the same number of pixels, the larger the CCD, the better the image quality. CCD size 1/2.7 inches (4.0mm×5.3mm) 1/2 inches (4.8 mm× 6.4 mm)1/0.8 inches (5.19 mm× 6.9/. Not a professional enthusiast, but for these two brands, Canon's color is brighter than the actual one, which is very popular with the audience. Nikon, on the other hand, has bright colors and can truly reflect the original appearance, but it seems that the color level is not as good as the former. Sony has a brand-name lens, which looks beautiful, not to mention anything else.