God's Palette

Then it seems to start talking about terminology.

③ aperture

Aperture is a device used to control the amount of light passing through the lens and entering the photosensitive surface of the camera body, which is usually inside the lens.We use the f-number to express the size of the aperture.For the manufactured lens, it is impossible for us to change the diameter of the lens at will, but we can control the amount of light passing through the lens by adding a polygonal or circular grating with a variable area inside the lens. This device is called the aperture.

Its size determines how much light enters the sensor through the lens.To express the size of the aperture, we use the F value, where F=the focal length of the lens/the diameter of the effective aperture of the lens.Aperture F value = focal length of the lens / diameter of the lens aperture.

The complete series of aperture values ​​are as follows: f1.0, f1.4, f2.0, f2.8, f4.0, f5.6, f8.0, f11, f16, f22, f32, f44, f64. The smaller the number after F, the larger the aperture.The function of the aperture is to determine the amount of light entering the lens. The larger the aperture, the more the amount of light entering; otherwise, the smaller the amount of light entering.To put it simply, when the shutter is constant, the larger the aperture, the more light enters, and the brighter the picture; the smaller the aperture, the darker the picture.

The types of apertures are: fixed aperture, cat's eye aperture, instantaneous aperture, and shutter aperture.

Aperture and shutter priority

In addition to the Auto mode, high-end digital cameras usually have two options, Aperture Priority and Shutter Priority, which allow you to decide a certain aperture value or a certain shutter value first in some occasions. Then match the appropriate shutter or aperture to present different depth of field (sharpness) or effects of the picture.

Aperture performs the following functions:

1. Limit the luminous flux entering from the lens and adjust the brightness of the image;

2. Reduce the residual aberration of the lens and improve the resolution;

3. Change the depth of field;

4. Make the light intensity in the center and edge of the screen uniform.

"Don't read it, don't read it." Mian Yu flipped through it casually.

④ Shutter speed

Shutter speed is an important inspection parameter of digital camera shutter. The shutter speed of different models of digital cameras is completely different. Therefore, when using a certain type of digital camera to shoot scenes, you must first understand its shutter speed, because When you press the shutter, you can only capture vivid pictures if you consider the start time of the shutter and grasp the timing of the release of the shutter.

Generally, the shutter of ordinary digital cameras is mostly within 1/1000 second, which can basically handle most of the daily shooting.The shutter depends not only on "fast" but also on "slow", which is the delay of the shutter. For example, some digital cameras have a shutter of up to 16 seconds, which is enough for shooting night scenes. "Noise", that is, there will be streaks in the photo.

In addition, mainstream digital cameras must have aperture priority mode and shutter priority mode in addition to automatic shooting mode.In aperture priority mode, the user decides the size of the aperture, and then the camera calculates how much light enters according to the ambient light and exposure settings. This mode is more suitable for taking pictures of still objects.

In the shutter priority mode, the user decides the shutter speed, and then the digital camera calculates the appropriate aperture size according to the environment.Therefore, the shutter priority mode is more suitable for shooting moving objects, especially digital cameras are very sensitive to vibration. Even a slight shake of the camera during the exposure process will produce blurred photos. This situation is more obvious when the long focal length is practical.

⑤Sensitivity

This is a specification formulated by the International Organization for Standardization (ISO) to quantify light sensitivity.The larger the value, the higher the sensitivity and the stronger the ability to absorb light. ISO sensitivity can be set and changed in the shooting menu, etc.

When the ISO sensitivity is doubled, the exposure is correct when the amount of light hitting the image sensor is halved.For example, when increasing the ISO sensitivity by 2 stop from ISO 100 to ISO 1, you need to increase the shutter speed by 200 stop accordingly, or shrink the aperture value by 1 stop before shooting.This is useful when you want to speed up the shutter speed to freeze a moving subject, or stop down the aperture to increase the depth of field (the area that appears to be in focus).In dark environments such as indoors, the shutter speed tends to slow down, which is the cause of blur caused by camera shake and subject movement.In this case, by increasing the ISO sensitivity, the shutter speed can be increased to reduce blur.If you want to shorten the aperture to deepen the depth of field or speed up the shutter speed to freeze the moving object, but because of the low amount of light, if the combination of aperture and shutter speed cannot solve the problem, you can increase the ISO sensitivity.

⑥ About the three elements of exposure: shutter, aperture and sensitivity (iso)

We all know that the three elements of exposure are shutter speed, aperture and sensitivity (ISO), but for those who are not familiar with it, it is difficult to figure out the relationship between the three.Below I will briefly introduce these three elements and the relationship between them.

Shutter speed

快门速度我们通常称快门，是指相机快门从开启到关闭的时间，通过这个来控制CCD的感光时间。通常我们用分数形式来表示，比如1/500表示快门开启到关闭是0.002秒, 1/100是0.01秒, 1/10是0.1秒, 1/2是0.5秒, 小7的快门是自动模式时是1/2~1/1000(有时也可以到1/1500),手动模式下是16~1/1000。

Let me briefly talk about some simple applications of different shutter speeds.

1. When shooting moving objects, we want to freeze a certain moment, such as the moment when an athlete sprints to the finish line, or the moment when water splashes, we usually use a fast shutter speed so that we can get a very clear picture;

2. It is still shooting moving objects, but we want to express the dynamics of the subject, so we can properly slow down the shutter speed and intentionally make the picture a bit blurred, so that it looks more dynamic. Another thing is that when we shoot water, slow down Click the shutter, you can get the effect of water flowing like silk;

3. When the light is dark, we need to use a slow shutter speed to increase the exposure. For example, when shooting night scenes, we often use a shutter speed of a few seconds, sometimes more than 10 seconds.

aperture

The aperture is a device used to control the amount of light that passes through the lens and enters the photosensitive surface of the camera body. The larger the aperture, the more light can pass through, and vice versa.The aperture values ​​we usually refer to as F2.8, F8, F16, etc. are aperture "coefficients", which are relative apertures, not the physical aperture of the aperture, and are related to the physical aperture of the aperture and the distance from the lens to the CCD.The larger the value, the smaller the aperture.The aperture range of our small 7 is f2.8~f8.0 at the wide-angle end and f4.8~f8.0 at the telephoto end, that is, the maximum aperture is f2.8 or f4.8, and the minimum aperture is f8.0.

There are generally some usages for the aperture as follows:

1. Use the aperture to control the depth of field. Under the same parameters, a large aperture has a shallow depth of field, and a small aperture has a long depth of field. Therefore, when we need to blur the background, we generally use a large aperture. On the contrary, if we want to get a larger depth of field, we can use use the smallest possible aperture;

2. When shooting silhouette effects, we generally use a small aperture.

Sensitivity (ISO)

Sensitivity (ISO), as the name suggests, reflects the sensitivity of the camera's CCD to light. The range of small 7 is 64 to 3200 (3200 is only effective at 110w pixels), iso64 is low sensitivity, and iso3200 is the highest.

Generally, low ISO can control the noise very well and get good picture quality. On the contrary, high ISO is much earlier, and the picture quality is relatively poor, especially when the ISO is above 800, the effect is almost unacceptable. ISO has a greater impact on exposure, low ISO requires a larger exposure, and high ISO requires a smaller exposure.

Before talking about the relationship between the three, let me talk about the concept of exposure. We call the process from opening to closing of the shutter, and from the beginning to the end of the CCD’s exposure, as exposure. From the previous introduction, we know that a photo is affected by the shutter and the aperture. Influenced by the three factors of sensitivity and sensitivity, in order to get a good and satisfactory photo, we need to properly combine the shutter, aperture and sensitivity.At this time, we introduce the concept of exposure, which is related to light intensity and sensitivity.

There are many exposure parameters stored in the digital camera, and the data obtained by the light metering system are calculated and compared, and then the camera gives the exposure parameters that the camera thinks are reasonable. This is the exposure mode of the automatic mode and the P mode;

Shutter Priority and Aperture Priority modes, that is, under your given shutter speed or aperture size, the camera calculates a reasonable aperture or shutter speed based on the metering data;

In M mode, this automatic metering calculation mode does not work, and all exposure parameters need to be set by yourself, so this function is generally only set for people who are more familiar with the camera’s exposure parameters.At this time, setting the exposure parameters requires us to set the shutter speed and aperture size according to our own experience to control the exposure, so as to obtain the works we are satisfied with.

⑦ focus

Focusing refers to adjusting the focus distance when using a camera. The English scientific name is Focus. Usually, digital cameras have a variety of focusing methods, which are auto focus, manual focus and multiple focus methods.

Focusing is also called aiming at light and focusing.Focusing is the process of changing the object distance and distance through the camera's focusing mechanism to make the image of the subject clear.

⑧Focus system

The so-called focusing system, simply put, is similar to the physiological function of the human eye, and is a module that imitates the function of the human eye.For digital cameras, low-end digital cameras use auto-focus systems, and some high-end professional cameras use manual focus systems.

Autofocus technology is one of the key technologies of computer vision and various imaging systems, and it is widely used in imaging systems such as digital cameras and digital video cameras.The traditional auto-focus technology mostly uses the distance measurement method, that is, by measuring the object distance, the image distance or focal length of the system is obtained from the lens equation to adjust the system so that it is in a state of accurate focus.With the development of modern computing technology and the increasing maturity of digital image processing theory, auto-focus technology has entered a new digital era. More and more auto-focus methods analyze and calculate image-related information based on image processing theory, and then according to control strategy Drive the motor and adjust the system to make it focus accurately.

A typical autofocus system should have the following units: imaging optical lens group, imaging device, autofocus unit, and lens drive unit.

The imaging optical lens group includes an optical filter, a zoom lens group and a focusing lens group; the imaging device is a CMOS (CCD) digital image sensor, which outputs digital quantities of image information; the autofocus unit uses a DSP chip as the core device, and the collection of image information , Calculation, selection of control strategies and generation of control signals are all carried out in this unit; the lens drive unit includes a stepping motor and its drive circuit, which accepts the control of the autofocus unit and drives the zoom lens group in the imaging optical lens group Adjust the position with the focus lens group, and finally make the image sensor output an image with accurate focus.