According to the optical principle, the focus has only one plane. This is the focal plane, and the area inside the focal plane is the brightest. Camera focus ensures that the camera gets the best image possible. When the subject is right on the focal plane when shooting Photo, it is in focus. Below are the necessary details you need to know about camera focus

Depth of field

The object on the focal plane is the sharpest. However, a part of the object outside the focal plane is also sharp – this is the depth of field. The depth of field in front of the focal plane is the depth of the foreground. Likewise, the depth of field behind the focal plane is the depth of field. The further away from the focal plane, the lower the sharpness, until it reaches a certain limit, then it becomes blurry. If you want to take a photo with strong bokeh, reduce the depth of field, otherwise increase the depth of field.

camera focus

Regarding the depth of field, there are calculation formulas and applications that directly generate calculation results. Put a formula for calculating depth of field.

camera focus

There are 3 common factors that affect depth of field. These factors are aperture, focal length, and focusing distance (object distance).

  • The larger the aperture, the smaller the depth of field.
  • The longer the focal length, the smaller the depth of field.
  • The shorter the object distance, the smaller the depth of field.

Autofocus and manual focus

The first step in focusing is to adjust the position of the focal plane so that it is properly in focus with the subject. There are two types of focusing methods: manual focus (MF) and auto focus (AF). When focusing manually, you turn the focus ring on the lens by hand and the focal plane changes, moving from nearer to farther. The pursuit of photography in the digital age is to facilitate quick keys. Manual focus is too troublesome. However, if the aperture is smaller than the focus point, it will cause autofocus to fail. Manual focus will be required.

camera focus

In the auto focus (AF) state, press the shutter button on the camera halfway and the lens will focus automatically. The pursuit of AF is convenience. For convenience, there are 3 common modes: Single AF, Continuous AF and Smart AF.

Single AF (or Single AF)

The camera only focuses once, and it will not change after alignment. Even if the subject flees and the camera moves, the focal plane distance will not change. This trick is suitable for shooting still objects and this focus mode is used in most cases.

Continuous AF

As long as you press the shutter button halfway, the focus system will still work. If the subject moves, focus will follow, ensuring the subject is always in the focal plane.

Smart AF

It can be freely adjusted between single and continuous depending on the condition of the object to be photographed. It’s also an AF mode that continuously autofocuses on moving subjects. This focusing method is also suitable for shooting moving objects.


Focus range

The farthest is infinity and the farthest point is the focal plane. At this time, there is no background depth of field, only foreground depth is left. If your closest focus distance is 0.5m, you can focus on objects within 0.5m and beyond, and objects within 0.5m will not focus. should not be developed. Note that the calculation method of 0.5m is the distance from the “point of focus” to the “camera sensor”, not the distance in front of the lens. The camera generally uses the symbol in the figure below to mark the position of the sensor.

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focus point

Hyperfocal length

As the focus distance changes, the depth of field also changes. When shooting landscapes, it is often necessary to be clear from far and near, in other words, to maximize the depth of field. When focusing on a certain point, the back limit of the back depth of field just drops to infinity. The depth of field range is greatest at this time. This point of focus is the “hyperfocal distance”. Aperture and focal length will affect depth of field, so different combinations of aperture and focal length will produce different hyperfocal distances. When photographing a starry sky, focus at infinity, then rotate the focus ring to find the hyperfocal distance. This will help get the biggest clear range and clear the foreground.


Ever-increasing focus

Manufacturers are also constantly improving the capabilities of camera and lens focusing systems. They do this to make autofocus “faster” and “more accurate”. You only need to half-press the shutter, and the machine can quickly find the object to focus on and successfully focus on it.

camera focus

Focusing principle

The principle of focusing can be subdivided into phase focusing and contrast focusing.

Phase focus

Phase focus mode is typically used by SLR cameras. Light entering the lens is refracted towards the focusing module, resulting in a phase difference. The focus module then judges the focusing method of the focus point position based on the phase difference.

Contrast tuning

Light entering the lens is projected directly onto the camera’s photosensitive chip. The main photosensitive chip determines the method of focusing the focal position by calculating the contrast of the image.


Recognition ability

Recognition capability is divided into linear focus, cross focus and double cross focus.

Linear focus

The linearity of the focusing module is divided into vertical lines and horizontal lines. When the lines of the object intersect with the vertical or horizontal lines, the camera can recognize and focus. If it is parallel, it will not be in focus.

Cross focus

Linear focus is one line, and cross focus is two lines, forming a “cross”, which improves focusing ability.

Double cross focus

Above the original cross, another cross is added. Thus, the focusing ability is stronger.

Target work area

There’s also the focus working area, which mainly reflects the number of focus points and the area each focus point can recognize.

camera focus

1. Full focus auto focus

If you turn on all focus autofocus, it is equivalent to putting the focus back on the camera. The camera will choose where to focus based on the entire frame. This focusing method is suitable for tracking shooting. When used in conjunction with continuous AF mode, the camera’s focus can continue to change as it tracks the moving subject.

2. Single-point autofocus

You can select a focus point by yourself using the arrow keys so that a specific place in the image is clear. For example, make sure the subject’s eyes are clear when shooting a portrait, or focus on a single flower in a sea of ​​flowers. This method is accurate and fast, but you have to choose carefully where to focus. In One-Shot AF (single autofocus) mode, press the shutter button halfway to activate and lock AF. This way, you won’t have any focus shift when you recompose your shot.

3. AF point group

Some of the more advanced cameras allow you to select a set of focus points. This increases the autofocus speed. Is Gooo to follow a small thing because it is difficult to follow the focus if there is only one point of focus. When you manually select an AF point, the camera automatically uses surrounding AF points to track moving things.


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