Aperture, shutter and sensitivity in basic course of SLR photography

Photography is an art, and a good photo depends on not only a photographer’s techniques, but also depends on their style and feeling.

Now, I’m going to talk about some of the most basic knowledge. Only by mastering these basic knowledges can deeply understand photography and learn photography. Otherwise, we can only take random photos.

Photography is about the art of light. Record the light and form a picture. Also, it is very important to master the exposure of a photo. You can not make a good picture without proper exposure. For exposure, you need to master the aperture, shutter, ISO, and undersatnd the relationship between them.

1. Aperture

The first one is about aperture. The aperture is a part of lens used to control the qperture size of the lens. There are different aperture sizes, which are represented by the letter F and a number of value, such as F2.8. The larger the aperture is, that’s to say, the larfer the aperture of the lens, the larger the aperture value and the more luminous flux. That’s may be more understandable for you.

The larger the number in the aperture valure, the smaller the aperture. For example, the aperture of F5.6 is less than that of F2.8. the main function of the aperture  is to control the luminous flux and depth of field of lens. It can also be considered as the stength of the virtual effect. The larger the aperture, the smaller the depth of the field, and the stronger the background virtualization effect.

On the contrary, the smaller the aperture is, the greater the depth of the field is, and the weaker the background blurring effect is. In order to undrestand and master the function of aperture, what you need to do now is to set the camera to mode A, which is aperture priority mode. Please refer to the manual for details. Maybe you are using an 18-55 on camera lens. Maybe you have replaced it with a large aperture focus lens. It doesn’t matter. First adjust the aperture to the maximum aperture allowed by your lens, such as F2.8 or F3.5, choose an object, like a cup. Then take a picture as close the cup as possible. Then try to keep the camera position unknow, and then adjust the aperture, repectively use F2.8, F4, F8, F16 to shoot.

Through observation, you will find that the smaller the aperture is, the weaker the background will be.

2. Shutter

Shutter should be a more familiar concept. Because taking pictures requires opening a baffle between the lens and the film (CMOS or CCD sensors in the digital age) to allow light to enter the camera and be recorded. This process is called exposure, but exposure is particular. A normal looking photo needs a certain degree of exposure, not too long or too short. If you use aperture priority, or program auto mode. It’s usually the camera that determines when the shutter opens.

Of course, you can take over and determine the duration of shutter exposure. Set the camera to speed priority mode. Nikon camera is in S mode. Canon camera is in TV mode, for other brands, please refer to the manual. Fix the ISO of the camera, such as ISO 100 function. Try shooting with several different shutter speeds, such as 1/100s, 1/250s, 1/60s/, 1/10s/, 1/2s. Try these shutter speed, and you qill find that the slower the shutter speed (the amsller the denominator number), the more blurry the picture will be due to hand shaking. In additon, the faster the shutter speed is, the larger the aperture will be, until the aperture cannot keep up with the maximunm aperture of the lens, which will lead to insufficient exposure of the whole picture.

Virtual aperture is one of the main functions of the aperture, the other is that the aperture will affect the shutter speed. When the ISO is fixed and the scene light is constant, the larger the aperture, the faster the shutter speed, that is, the shorter the exposure time. In the same lighting condition, large aperture means a large amount of light, so there is no need to extend shutter exposure time to make up. Vice versa.

It can be seen that when the shutter speed is very fast and the exposure time is very short, the camera needs to use a large aperture as far as possible in order to reach the normal exposure value. When the maximum aperture does not meet the exposure amount, the picture will show insufficient exposure.

With the increase of the shutter, the exposure time increase gradually. When the exposure reaches the normal value, the maximum aperture is no longer needed. With the extension of the shutter, the aperture is gradually reduced. If the minimum aperture is not enough to reach the normal value, the picture will show overecposure. Of course, this group of picture was tested in the indoor light, and did not meet the conditions of overexposure. It’s easy to overexposure when it’s sunny outdoors.

3. Sensitivity (ISO)

This is a rather difficult term to understand. Sensitivity is the sensitivity to light. In the era of film, the sensitivity is determined by the film purchased. The sensitivity is fixed and is an attribute of the film itself. In the digital era, the sensitivity of electronic sensors can be set freely within a certain range, which is much more convenient than the original film era.

The larger the ISO number, the more sensitive it is to light. When the aperture and shutter remain unchanged, increasing ISO can improve the exposure of the picture. When the aperture is fixed, the higher the ISO, the faster the shutter speed. When the shutter speed is fixed, the larger the aperture, the lower the ISO.

It should be noted that although ISO can make up for the compensation of exposure, it will also bring noise. With the continuous innovation of technology, the noise will be less and less under the same value, but it will still exist obviously.

4. What is noise?

Noise is mainly due to the electronic image sensor (usually CCD or CMOS) in the process of receiving light and converting it into electrical signal output. These particles are not found in the object, usually due to electronic interference.

For example, with the following photos taken with different sensitivity as a reference, we can see the different levels of noise in the picture, and we can have a very intuitive understanding of what noise is.

5. When would the noise occur?

There are two cases of noise, usually using high sensitivity to shoot, so it will produce noise. In daily shooting, almost most of the noise is caused by the use of high sensitivity. The other is long exposure. Digital camera uses electronic sensor instead of traditional film to image. Therefore, under long exposure, the electronic sensor will heat up, and the increase of heat will lwad to sensor’s photosensitive performance, which will always form noise on the screen. There fore, noise is not the object of the subject, but also we do not want in the final photo, but it can be completely avoided.

Of course, with the development of science and technology, most SLRs and micro SLRs can hardly see noise below ISO1600 or evern below ISO3200, but they still have an impact on the image quality. The noise level of each camera is also different. So you need to do a lot of trial shots to understand the performance of your camera and the level of ISO noise you can accept. There is no knack, only by experience and more practice will you can learn.

Therefore, aperture, shutter and ISO determine the exposure of a photo. The three complement each other, also known as triangular relationship.

Tags : Aperturesensitivity ISOshutterSLR photography

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