What is focus? In photography, it’s practically married to sharpness. An image that is completely sharp is said to be in-focus. An image that’s completely blurry is said to be unfocused. The same metaphor applies to your mind. When you concentrate, your mind is sharp. You are focused. When you’re confused, you lack 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, I want to 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 inside. The size of the hole the light travels through (the aperture) determines how focused those 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 correspond to smaller apertures. At F22, the depth of field (or focus range) is much larger than at F4. You can use depth of field to emphasize certain parts of an image. That’s one reason why F4 is such a good aperture for taking portraits. You can focus on the eyes alone while the background gets completely blurred out. The small depth of field makes your friend’s face stand out from the background.
With that explained, here's how to use focus to improve your images:
Don’t always put everything in focus
There are 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, as we have just discussed, look a lot better when the background is somewhat out of focus. The effect is akin to bringing your friend into the studio and placing him or her in front of a solid colored background.
I should also mention that it’s simply harder to draw attention to things that don’t stand out on their own. When we focus our eyes, we do something similar. You might not notice it, but everything else in your peripheral vision appears a little more hazy. Most of the time, only one part of your images should be truly sharp. Let the rest get a little fuzzy so the sharp part stands out.
Understand visual depth
What is depth? It’s a measure of the three dimensionality of things. Imagine holding an apple out in front of your face. The apple is fairly three dimensional. It recesses into the background. It isn’t as three dimensional as your entire arm sticking out in front of you, but it is has a sense of depth.
Contrast the apple with a wall or a flat piece of paper being held out in front of you. Neither have that much visual depth at all.
As it turns out, this is pretty important in photography. There are some photographic situations where it really doesn’t matter how large your depth of field is. You don’t need a huge depth of field to focus on a person standing in front of a mural, for example. Any aperture between F8 and F11 will do.
Just think of it this way. The more visual depth you 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 the image as sharp as possible. You’ll want to use a smaller aperture to get the largest possible depth of field.
Test it for yourself
There’s no better way to see how the depth of field can change than to simply try out a bunch of different aperture values. Your camera’s aperture priority mode is ideal for this. You can pick any aperture value you want, and your camera will pick a corresponding shutter speed to give you the right exposure. This is a great way to see how the aperture affects the depth of field, which in turn affects how the focus works on your camera.
Start off with a portrait at F4. After that, go to F8 and then try the same portrait at F22. Be aware that you’ll need keep your camera stable for the last shot. A smaller aperture means your camera gets less light, and if you are in aperture priority mode, your camera will automatically pick a slower shutter speed to compensate. In short, your picture will be subject to camera shake.
Focus is nothing more than the degree of sharpness at a certain point. You can focus on different things, or you can change the aperture to get a larger or smaller depth of field. Either present you with a number of creative options that will help you draw attention to the most important parts of your image. Keep the depth of field small for closeups of your friends and large when you’re doing big open landscapes. It’s a simple rule that will give you some great results.
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