A good photo is a photo with a strong message. Focus is a tool you can use in order to clarify your message. How you place the focus on your subject will be crucial to the way other people experience your photo. Taking photos that are really sharp is what many photographers aim at, but not all parts of a photo need to be in focus for a photo to be sharp.
Correct focus is crucial
Simply put, the focus is the part of your photo that is sharp. To focus means adjusting sharpness. You can place your focus on many parts of your image: up close, the background, up, down, to the right, to the left, or on a corner of the photo.
Many people think that what camera you use decides how sharp images you can get, this is, however, not quite right. An image is produced when light from the subject, either reflected by the subject or emanating from the subject, passes through the individual lenses of the photographic lens and is projected onto the sensor. A modern photographic lens is comprised of multiple lenses and it is the interplay between these pieces of glass that eventually determines the sharpness of a photo. The construction of the lens and the camera housing is important to how fast and how precise you can place your focus.
Say hello to a fisherman from Kenya. Focus clearly underlines the message of a photo and consequently its purpose. 12-2mm (on a 12mm), f/4, 1/1600 seconds, ISO 200
Being able to shoot photos that are really sharp is one of the most important skills of a photographer. If the focus is just a tiny bit wrong it can ruin the entire photo. If the focus is on something else than the main subject of the photo this is guaranteed to be the first thing that catches the eye of someone viewing the photo.
Using focus correctly will help direct the attention of the viewer to where you want it to be. If the focus is just right, the result will be an extremely powerful image.
However, it takes a lot of skill to be able to focus swiftly and correctly. Take your camera outside and choose a scene with a lot of action, such as, for instance, a marketplace. Try taking many different photos where you focus close up, far way or to the side.
The photographic lens is very important to the sharpness of your photos.
Depth of Field
How much of your subject will be in focus (be within the depth of field) depends on several parameters. One parameter is the focal length of your lens as well as the distance between you and your subject. Another parameter is the aperture you choose for exposing your photos. A high f-number results in a large depth of field.
Wide-angle lenses (with a focal length of 14-24mm) are capable of producing an enormous depth of field, conversely, tele lenses (with a focal length of more than 85mm) often produce an extremely limited depth of field. You can use both features to your advantage. You should use wide-angle lenses in combination with high f-numbers (e.g. f/16) if you want as large a part of your photo as possible to be sharp. Choose a tele lens and a very low f-number (e.g. f/2.0) if you want to limit the depth of field.
Different Ways of Focusing
As focusing is very important to photography, the focusing mechanism is one of the most highly developed parts of a modern camera. It is this technology that allows you to focus in no time. Today, modern cameras are able to focus quicker and more precisely than ever before. This has made it easier to capture subjects which were previously outright impossible to capture, or at least very difficult to work with. Modern cameras can even do this almost soundlessly and without using very much battery power. Generally speaking, there are two ways of focusing: auto focus and manual focus.
For a photographer it is very important to know when to use what kind of focusing. It might, for instance, be a good idea to focus manually when you are taking macro photos (close-ups). Photo by Karina Mikkelsen
The most widely used way of focusing is auto focus. Many photographers feel that using auto focus is the easiest way of focusing, and this is true in most situations. When you use auto focus the camera and the lens cooperate on focusing on one or more points defined by the photographer. There are actually different varieties of auto focus. The various makers of cameras may call them by somewhat different names, but fundamentally they are the same.
AF-S (auto focus-single): The camera starts to focus once the shutter is depressed halfway or when the AF-ON button is activated. Once the camera is able to find a focus point an icon will appear in the viewfinder informing the photographer that focus has been placed as wanted. You can confirm this information by taking a quick look through the viewfinder. This type of auto focus is suitable when shooting subjects that remain at a fixed distance from you. If your focus is not placed right the camera will refuse to expose your photo once the shutter release is depressed. This means that you can be quite sure that your subject is actually in focus when you hit the shutter.
AF-C (Auto Focus-Continuous): The camera focuses continuously as long as the shutter release is depressed. In theory, this focusing mode works in the same way that a video camera does and your subject will remain sharp even if it moves closer to you or away from you. This allows you to concentrate on the composition of your photo and take photos of the subject while it is moving.
The disadvantage of using this tool is that you cannot be certain that every single photo will be really sharp. The advantage is that the camera takes photos every time you depress the shutter release no matter if your subject is in focus or not. In some cases, this process can lead to some good results that you would not have obtained if you had set your equipment in the AF-S mode. If you want to lock your focus on one specific point while you continue working on composing your photo, you need to depress the button labelled AE-L/AF-L. You should, however, be aware of the fact that depressing this button also freezes light metering. What mode of focusing you prefer is a matter of personal preference, however, the auto focus modes of modern digital cameras are by now so efficient that you can rely on them for most purposes.
One of the fastest boats of the world, shot doing appx. 150 km/h. In this kind of situation efficient auto focusing is critical. 70-200mm (on a 200mm), f/2.8, 1/3000 second, ISO 400, -0.7EV
Even professional single lens reflex cameras can be set to manual focus. Using auto focus is not always an advantage. Once the manual focus mode (M) has been selected, it is up to the photographer to focus by manipulating the focus ring.
Using auto focus becomes increasingly difficult the darker your subject or the less contrast your subject has. This particularly applies if you take photos without using any auxiliary light (AF-assist) or flash. Another problem about using auto focus is that this mode is not very good for macro photography (close-ups) where you will often have problems finding an efficient and contrast rich focus point. The solution to these two problems is opting for manual focus, this mode is, by the way, very good for face portraits.
In some situations manual focus can be far more efficient than auto focus.
Most dSLRs allow the photographer to choose precisely on what parts of a scene he wants focus by using several focusing points in the viewfinder.
Many cameras allow you to choose from different modes such as single-point/single-area focusing, dynamic area focusing, and dynamic area focusing with closest-subject priority. As mentioned before, the different camera producers may have different names for these modes, but the function is the same. The reason for having that many different focusing modes is the fact that there are not two subjects that behave in the same way. If your camera allows you to choose between these different focusing modes you will be able to learn more about the details by consulting your manual.
Focus points are often placed very differently in different camera models.
These two examples are from a modern camera (left) and an older camera model (right). As you can see there are many more focus points in the new camera. The cross-type sensor is the most efficient type of sensor because it allows you to focus both vertically and horizontally.
Single point focusing is very good for motionless subjects or for subjects that move in predictable patterns. You will only be able to focus on a subject that is located within one single focus point in the viewfinder of your camera.
Dynamic area focusing is used for shooting subjects that move in an unpredictable way. Using this tool the camera collects information from all focus points and it follows your subject for you.
If instead you use dynamic area with closest-subject priority the camera is in charge. This mode is very good for shooting for instance team sports because in this situation you always want focus to be on the player that is closest to you. Consult the manual of your camera to get precise information on the possibilities of your camera.