I often see questions on photography forums like this: “How can I repair a blurry, out of focus image?” Honestly? From my point of view nohow, so it’s way better to forget it! However, there are some tricks on how to recover a badly focused photograph in post-processing, but to be fair, it will never be perfect, because the original picture is screwed up already. To take tack sharp photos at all times, we should understand how the camera autofocus system works. Let’s take a peek on how the camera and lens collaborates to create crisp and sharp images!
What is autofocus on a camera?
Autofocus is a focusing system that adjusts the lens of the digital camera to focus on the subject what we are photographing and make sure it’s sharp. There are two types of autofocus systems, active and passive.
Active – Sensors identify the subject’s distance from the camera by shooting a red beam on the subject then bouncing back to the camera to figure out the distance, and transmit the information to the lens, which adjusts the focal length accordingly. The big advantage of the active autofocus system, that it’s possible to use it in low-light situations where the passive autofocus system fails. However, it has a drawback too. The active autofocus system works only for static objects because it takes time for the beam to get back to the subject.
Passive – This system uses a different technology and working with contrast measurement or phase detection.
- Contrast measurement works by looking for contrast in an image, and adjusts the lens until the picture is in focus. The process while the system finds the area with the most contrast, is called hunting. It’s great for static objects, but unfortunately, a bit slow.
- Phase detection can be found in DSLR cameras and uses a beam splitter to divide the incoming light into two different groups of image sensors with a microlens above them, then it creates 2 images. If the images are matching, it means our subject is in focus, if they don’t, then our subject is out of focus. Great for tracking objects!
When we look through the viewfinder, we can see small empty squares, they called focus points. That’s what the camera uses to focus on the subject. As it’s obvious, entry-level cameras have fewer autofocus points than professional cameras. Some cameras have a 9 point system, while others have 11, 51 or even more! It means, with cameras that have more focus points, we have more alternatives to fine-tune the focus. There are two different types of autofocus points, vertical and cross-type.
- Vertical sensors are one dimensional and only detect contrast on a vertical line.
- Cross-type sensors are two dimensional and detect contrast in both vertical and horizontal lines too. This kind of sensor is much better than the vertical one, as it is more precise.
We can either let the camera to choose the autofocus points or we can disable this option, and choose autofocus points ourselves. In that case, we have control over the focus. By using this alternative our pictures will definitely improve.
However, sometimes there are circumstances when autofocus doesn’t work, especially when it’s too dark for the autofocus to operate, or the subject is too near to us. In those cases, the camera won’t let us take a picture. What we could do is either switch to manual focus, and adjust the focus manually, or if the subject is too close, try to move back until the camera finds focus.
There are different autofocus modes for different scenarios. By selecting one of them, we control how the camera focuses on the scene. They can be found inside the camera menu.
- Single-shot autofocus One-shot (Canon) or AF-S (Nikon) mode is the simplest and most reliable mode, which is great for still pictures, like static objects or landscapes, etc. When we press the shutter button half-way down, and the camera finds the focus, it remains locked, then we can recompose the image if needed.
- Continuous autofocus Al Servo (Canon) or AF-C (Nikon) mode is used for tracking objects. This mode basically evaluates the subject’s movement and expects it’s place in the future by estimating it’s speed from previous focus distances. It requires the photographer to keep the shutter half-way down to follow the subject’s movement. Keep in mind to not leave the camera on continuous autofocus mode all of the time, because the autofocus system tries to find any movement, and it can lead to an out of focus image.
- Hybrid autofocus Al Focus (Canon) or AF-A (Nikon) mode is fundamentally a mixture of the two modes explained above. In this mode, the camera finds out if the subject is static or moving and switches modes accordingly. Principally it’s designed for beginners.
Autofocus area modes
Most of the DSLR cameras have different autofocus area modes, which helps us where to focus on the image.
- Single point autofocus area mode In this mode the camera uses only one focus point, that we can adjust in the viewfinder up, down, left or even to the right. This autofocus mode is the most accurate from all of them. Mainly used for still subjects, like portraits, landscapes, etc.
- Dynamic autofocus area mode This mode is very similar to single point autofocus area mode, as once we choose our one focus point, the camera starts to track the object and keep focus on it. It’s mainly used for sports and wildlife photography.
- Auto-area autofocus mode Our camera chooses the focus point automatically, depending on what we are photographing. Basically, the camera focuses on the closest object on the picture.
- Group area autofocus mode As its name implies, it uses a group of autofocus points to focus on the subject. We can guide the camera to focus on a particular area of the image. Great for tracking unpredictable movements.
That’s it in a nutshell! This article is only a short version of the autofocus system, and there’s definitely much more to learn. It could be a great idea to read our camera’s manual too! Once we learn how to focus correctly, we will be able to take sharper images in no time.