Updated: Jun 24, 2020
In photography, the most important thing in any photograph is sharpness. Any image which is completely sharp is said to be in-focus whereas any image which is completely blurry is said to be unfocused. The same metaphor applies to our mind. When we concentrate, our mind is sharp. We are focused. When we are confused, we lack focus. The camera is a light-tight box which is used to expose a photosensitive surface (a film or a digital sensor) to light. In order to focus the light onto the surface, most of the cameras (and your own eyes) use a lens to direct the light. While some of us prefer auto focus and some of us like manual focus. As you are about to learn, you can use focus to direct your viewer’s attention to the most important parts of a scene. Here’s how.
Before we get to the tips themselves, let's discuss the mechanics of focus itself. In order for a camera to create a focused image, it takes light and runs it through a lens, concentrating the rays on the image sensor or film inside. The size of the hole through which the light travels, the aperture, determines how focused those light rays are once they hit the sensor. Smaller holes do a better job of focusing light than larger holes.
In terms of actual camera settings, larger f-numbers means smaller apertures. At F22, the aperture is very small, thus the depth of field (or focus range) is much larger than at F4, where aperture is wide open and we get a shallow depth of field. We can use depth of field to emphasize certain parts of an image. That’s one reason why F4 or F1.8 is such a good aperture for taking portraits. We can focus on the eyes alone while the background gets completely blurred out. The shallow depth of field (at wide aperture - F4 or F1.8) makes your friend’s face stand out from the background.
Don’t always put everything in focus
You'll get a lot of situations where you don’t really want the entire image to be in focus. Backgrounds tend to get in the way, and they will distract your viewer from the point you are trying to make. Portraits look a lot better when the background is somewhat out of focus, it puts the attention of the viewer directly on the subject.
The more visual depth we have, the more important focus becomes. Landscapes have an incredible amount of visual depth, all the way from the foreground to the background. It’s important to capitalize on that depth by making everything present in the image as sharp as possible. You’ll want to use a smaller aperture (F22) to get the largest possible depth of field.
The focal length of any lens is the distance between the lens and the image sensor when the subject is in focus. Focal length is usually stated in millimeters (e.g., 28 mm, 50 mm, or 250 mm). In the case of zoom lenses, both the minimum and maximum focal lengths are stated, for example 18–55 mm and 70–200mm.
Focal Length and Angle-of-View:
The angle of view in photography is the visible extent of the scene captured by the image sensor, which is called as an angle. Changing the focal length changes the angle of view. Wide angle of views capture greater areas, small angles smaller areas. The shorter the focal length (e.g. 15 mm or 18 mm), the wider the angle of view and the greater the area captured. The longer the focal length (e.g. 100 mm), the smaller the angle and the larger the subject appears to be.