Basic knowledge of photography (II.)

http://www.canon.com.cn/canon_liveview_cn/4.htmlMetering Mode • Metering Mode

The purpose of the metering operation is to obtain the correct exposure , when the exposure is appropriate, to obtain a satisfactory picture, or a part of the photo may be due to exposure or exposure. For example, the following two photos are taken at the same time, one metering position is in the high reflectivity of the sea, the other spot is the right low reflectivity of the person. Shooting in automatic mode, visible with the sea metering, the camera's exposure settings are clear shooting out of the sea, but the people and the pier appears to be insufficient, when the person to light, then see the sea into a white, overexposed.

The SLR camera allows the user to specify the metering mode, and there are about four common metering modes available: Central weighted metering , partial metering , spot metering , and evaluative metering .

• Center -weighted metering

Center -weighted metering, the camera metering unit separates the overall metering value of the camera: the central part of the metering data accounted for the majority of the proportion of the central outside the metering data accounted for a small proportion, mainly used for metering auxiliary . After a weighted average of these two values, the camera processor obtains the last-shot metering data. Central metering is a traditional metering method, most of the camera's metering algorithm is focused on the center of the screen about 2/3 of the area, the surrounding area is also given to a certain extent. For example, in a Nikon camera, the central portion of the metering occupies 75% of the overall metering ratio, while other areas of the metering data occupy only 25% of the scale.

Central metering mode is mainly used when the subject is in the center of the screen, but if the subject is not shot in the center of the screen or in the backlight condition , Center-weighted metering mode is not applicable.

For example, the following two photos are taken using aperture priority mode, aperture size F8, the selected metering point location is different, the final result difference is very obvious. The left side of the bright area for light exposure metering, the right side of the shadow area for metering, metering system to ensure that the shadow part of the correct exposure, will reduce the shutter speed, resulting in the sun exposure to the area and the sky overexposed.

• Partial metering

Partial metering, only a small area in the center of the screen for metering , the range of metering area is about 8%. Local metering mode is often used for some complex light scenes, because the need to get more accurate exposure, the use of local metering can be accurate exposure of the subject of the photograph.

Local metering is suitable for some Complex light lines , when the subject and background have a strong contrast , and are photographed When the proportion of the screen is not large, the use of this method of metering is most suitable, such as in the stage, performance, backlight and other scenes.

• Spot Metering

spot metering, only a small area in the center of the screen for metering, most of the camera's spot metering area of 1% to 4%, the camera according to the narrow area measured by the light as exposure according to data. Spot metering, the metering point is not necessarily the center of the composition, or after the metering need to re-composition, this is to take the light and shade more average area of the metering value, when the metering is completed using the exposure lock button to lock exposure.

Spot metering is a fairly accurate metering method, but also because the exposure of the reference point is small, so sometimes the drop will be relatively large, so it is the most difficult to master a metering mode. The comparison applies to stage photography, personal art photo, news feature photos and so on. For example, spot metering is used for metering, but the final exposure parameters are different due to the spot metering position. The left one is measured with bright lights, with the aim of highlighting the light as the theme, ignoring the background and other details; On the right is the meter to the lamp holder, the purpose is to show the details of the surrounding environment, so that the whole picture is very bright, but it is obvious that the light part has been exposed. Therefore, the spot metering position depends on different circumstances to choose.

• Evaluative metering (split metering, matrix metering, multi-zonal metering)

Evaluative metering, the screen is divided into several metering areas, each region independent metering after the integration of weighted calculation of a whole exposure value . This metering mode in the shooting light distribution evenly, there is no great contrast of the scenery when the good performance, but in the light complex or the subject and background light has a strong contrast , the evaluation of metering prone to errors, then according to the situation of light to adjust exposure compensation at any time, To ensure the correct exposure.

The Multi-zone evaluation is the most advanced intelligent metering method, suitable for large scenes of photos, such as scenery, group photo, etc., in the shooting light source is more positive, light more uniform scene when the best effect.

• Exposure lock button (AEL)

AEL is the exposure lock. Simply put, when we press the AEL button, the camera exposure value will only be fixed on the current metering parameters, even if the photographer change the shooting angle or shooting environment, the exposure parameters will not change. AEL and AFL are often implemented by the same button on the camera, and through the camera menu we can customize the button to AEL or AFL.

Autofocus mode for viewing window shooting TTL phase difference detection method

TTL phase detection is a way to decompose the light through the lens and use its phase difference to perform AF. The digital SLR camera has a special auto-focus sensor, which is used to focus on the TTL phase detection method. This method can realize high-speed coking by detecting how many differences exist in the direction of the focus before and after. TTL is the meaning of through the lens.

• One-time AF mode (AF.S)

single focus mode, when the camera completes the focus when the shutter button is half pressed, the finger does not loosen, and the focus is locked without pressing down . At this point the direction of rotation or the moving position of the lens foreground will not change the focus. The selected focus in the viewfinder is shiny in a single-focus mode: The focus is not on the on-time focus ring, and when the focus is already on the on-time focus frame will turn red and accompany the beep.

In practice, the subject part of the shooting object is not always in the center of the picture, but often left or right. If you press the shutter directly to the front, the camera will take the object in front of the focus to the distance of the building trees and so very clear, and the more recent figure is blurred. The way to solve this problem is to use a single focus mode. First, the camera to stand on the edge of the image of the characters, and then half-press the shutter when the viewfinder will show a red box in the figure shows the focus on the place, then the finger do not move, gently turn the camera framing the person and background are placed in the position, and then gently completely press the shutter, so the photos taken, The focus is on the more recent characters, the people are the clearest. In this way we are generally referred to as the focal shift. Therefore, the single-shot focus mode is stationary for the object, or it is convenient to change the composition.

• Continuous AF mode (AF.C)

continuous Focus mode when the shutter button is half pressed, the camera continuously focuses on the subject . The subject is constantly changing position and distance in the picture, the camera keeps it clearest at all times, and when the shutter is pressed completely, it can take a clear picture of the body.

Like a man running across from the other side. When he was 15 meters away from us, we aimed at him and half pressed the shutter, then the camera locked him in the focus, he continued to run, closer to us, then the camera will always keep him as the focus of continuous adjustment, whether he is 8 meters or 5 meters, you always press the shutter to take the photo , the people running in the film are clear. Because the camera has been focusing in this mode, it is easy to snap the shutter at any time.

• Auto Select mode (AF.A)

In auto-smart focus mode, the camera first assumes that the subject is not moving, and that the shutter is automatically focused and the focus is shining. There are 3 conditions under which you can keep the shutter state half-pressed:

1. The shooting position does not move, the subject does not move. Moving the camera in the direction of the re-composition, the focus does not change any changes in the ear close to the camera can not hear the focus sound, exactly the same as the AF.S mode.

2. Move or shoot the object before and after the shooting position. The camera will start to automatically focus continuously, and the focus will be heard, but the focus is not shining. This is equivalent to AF.C mode.

3. Change the distance before changing the lens direction or the original focus target to leave the original focus camera auto-refocus.

real-time display of Shot AF mode

Many of the micro-cameras do not have the AF mode mentioned above, because there is no viewing window at all, only real-time display of the AF mode. For example, Pentax K01 has only four modes of face Detection , tracking , selection , and focus . Each camera's real-time shooting autofocus mode is different, more common is the face detection and focus mode Two, several other modes excerpt from the Pentax SLR camera manuals.

• Face Detection mode

Face recognition mode, when the character's face is detected, the focus frame will automatically display in the screen of the LCD monitor, even if the character appears to move, the focus frame can be automatically tracked. When the focus frame position coincides with the face you wish to focus on, press the Autofocus Start button to start autofocus and shoot.

• Tracking Mode

Track the body with the right focus and shoot even if you don't focus accurately.

• Multiple auto-focus modes

Focus on the desired area, divide the sensor into N regions, and set the AF area to the desired range size. For example, Pentax has the opportunity to divide the sensor into three (9 x 5) regions, and the auto focus area can be selected as 1,9,15 or 21 in 45 regions.

• Select Mode

Sets the focus area in number of pixels.

• Focus mode (central mode)

The focus is fixed in the central part of the screen, focusing only in the central restricted area, and is the most commonly used AF system.

Basic knowledge of photography (II.)