How to focus quickly and clearly when shooting DSLR video?

Previously, a friend of Quanquan happily told Quanquan that he had changed his equipment to Sony’s flagship mirrorless camera A7S2. He told Quanquan that the reason why he chose this machine was because it was claimed in the advertisement. The machine can realize the autofocus function in mirrorless (SLR) shooting.

But just a few days later, this old friend of Quanquan came to complain to Quanquan. He said that the autofocus of the machine was really smart and fast when shooting still images indoors, but Once you go outdoors with a cluttered background or when shooting subjects with complex movements, the camera's autofocus function is simply sluggish.

It seems that advertising is advertising after all. According to Quanquan’s understanding, there is currently no SLR (micro-SLR) that can achieve perfect autofocus function. So, for small and medium-sized teams and individuals who use SLR (mirror single-lens) as their main shooting equipment, how can they achieve fast and clear focus?

First of all, we have to understand the focusing principle of SLR.

According to normal visual experience, people focus on target objects when looking at things and automatically ignore non-target subjects. According to this principle, people invented the photoreceptor (formerly film) and the lens.

So, when people find that the target subject is not clear in the picture, they will subconsciously feel anxious due to the incomplete visual information obtained, and subjectively regard such a picture as a "mistake picture". This is why we emphasize that the most basic condition for a qualified image is clear and correct focus (of course, in some special types of image works, out-of-focus images can be allowed, such as some impressionist and stream-of-consciousness MV works) .

Having talked about so many principles, how do you achieve clear focus? Many friends with shooting experience will find that it is relatively easy to focus when shooting some relatively still subjects, but once they encounter moving subjects, focusing seems to become a difficulty in shooting. In fact, automatic focus is not used in professional film and television production processes. The cameraman usually is equipped with a focus puller who is responsible for controlling the focus.

First, shoot the subject with a simple and relatively static background. Many people are accustomed to using the autofocus function of the SLR to focus on the subject clearly before pressing the video capture button to record the video, but Quanquan does not recommend this method. Because this method usually requires turning on the autofocus switch (AF) function of the lens first, after pressing the shooting button, the photographer usually does not have time or forgets to turn off the autofocus switch, so it is difficult to cause movement in subsequent shots. Focus and record the sound of the focus motor working, which affects the final imaging effect.

Circle’s suggestion is to turn off the autofocus (AF) switch of the lens before shooting and set it to manual (MF) mode. Then, use the camera's LCD screen to zoom in on the subject to get clear focus. Usually, the camera's magnification function is 5x and 10x. It is recommended to zoom in to the maximum to focus under limited circumstances. After repeatedly verifying that the focus is clear, press the shooting button to record the video.

So, for the second relatively complex shooting situation mentioned above, how should we keep the focus clear?

Quanquan mentioned the relationship between f-number and aperture in the previous sharing "Small and Medium Cost Video Production Equipment Configuration Guide (Basics)". Simply put, the smaller the f-number, the larger the aperture. Some friends may have used cameras that are mainly used for shooting news, records and other subjects. Such cameras are usually able to achieve automatic focus. Of course, this has something to do with the focusing element, but if you carefully observe the pictures taken by the cameras, the depth of field in the pictures is usually deeper.

"Depth of field" is a concept that many friends often come into contact with when shooting SLR. Simply put, depth of field is the clear range in the picture.

So cameras that can achieve automatic focus generally have a smaller aperture, which means that the f-number is very large. Therefore, after we enlarge the f value of the SLR (micro-SLR), the aperture of the lens becomes smaller, so that the clear range in the picture becomes larger. Even if the subject moves to a certain extent at this time, it will not be easily out of focus.

However, for SLRs and mirrorless cameras, they are often limited by the sensitivity (setting the sensitivity too high will produce noise and affect the use of the picture). Circle recommends the following methods to reduce the size of the image. Maintain the normal exposure of the picture regardless of the aperture.

1. Increase ambient light

Use various ambient lights at the shooting site, such as various indoor lamps and natural light outside the windows. If necessary, you can add special shooting lamps, such as LED portable lights, etc.

2. Reduce the shutter speed

Generally speaking, when we are shooting videos, we generally do not easily change the shutter speed of the camera, but it can be appropriately adjusted when the subject does not move much. Lower the shutter speed to 1/30s to allow more light into the camera and maintain normal exposure.

In addition, Quanquan recommends using some auxiliary equipment to help you obtain better focusing effects.

Magnifying glass viewfinder

There are two main types, one is installed on the camera’s LCD screen to enlarge the display screen, and the other is installed directly on the viewfinder for Zoom into the camera viewfinder. Circle here recommends that you use the first magnifying viewfinder. This kind of magnifying glass makes it easier to grasp the clarity of the focus by directly observing the display screen. In addition, because the magnifying glass itself is larger, it can provide additional support points when shooting close to the eyes, which is beneficial to shooting some sports shots.

External monitor

Quanquan introduced this kind of external monitor to you in the previous "Small and Medium Cost Video Production Equipment Configuration Guide (Extended)". This kind of monitor is usually connected to the camera through a high-definition cable and can display the camera's viewfinder in real time. In order to make it easier for users to focus, this type of monitor generally has auxiliary focus functions, such as the display of focus peak, and can also be equipped with a hood to Convenient for shooting in outdoor strong light environments. Of course, compared to magnifying glasses, external monitors are generally more expensive.

The above equipment can be purchased on a certain treasure or large e-commerce platform. Of course, in addition to skills and equipment, Quanquan’s most sincere advice to everyone is to practice more. In the filming of film and television dramas, faced with some difficult-to-control moving shots, the camera team usually has to simulate the movement trajectory of the actor (subject) multiple times to maintain a clear focus during the entire movement, so don’t worry about shooting repeated shots. Taking a few more shots can greatly increase the chance of getting a perfect picture, and it will also make it easier to edit and select materials in post-production.