Back to Basics: Depth of Field - 3 Elements
When it comes to depth of field, we all immediately say: aperture. Because aperture simply determines the depth of field... or is it just a bit different? Because why does one photo at f4 aperture differ from another at f4?
First, let's go back to what depth of field is. In the blog about focusing we learned that you can only really focus on 1 point (1 distance) and that the rest is out of focus. But with depth of field you can 'stretch' the sharpness a bit, so parts in front of and behind your focus point also become sharper for your eye.
And how much in front of and behind your focus point becomes sharper (how many cm or m) is called depth of field. With a shallow depth of field, your model's eye is sharp and the tip of the nose and ears are already out of focus.
With a lot of depth of field, the tree in the middle, the skyline on the horizon and the bushes in the foreground are all sharp. This way you can determine whether the viewer likes to look through the entire image (everything sharp) or whether the attention goes to the eyes of your model (eyes sharp, rest a bit more vague).
The aperture allows you to adjust the depth of field. A small aperture (large number such as f11 or f18) provides a large depth of field, so everything is sharp.
A large aperture (small number such as 2, 2.8 or 4) provides little depth of field, so a blurred background.
But you can still see differences between photos. With one photo at f4 you have a very blurred background and with the other photo at f4 everything seems much sharper. How?
Actually, the aperture only controls 1/3 of the depth of field. There are 2 more elements that provide more or less depth of field. And they can reinforce or counteract each other.
Which are those?
If you use a telephoto lens, you have much less depth of field. A telephoto lens has the property that the background often becomes blurred. Shooting a portrait with a very sharp background with a telephoto lens? That will be a challenge. But with a portrait you often want a blurred background, and then the telephoto lens with a large aperture (2x shallow depth of field) is a very good option.
Are you using a wide angle lens? Then everything is almost always sharp. A blurred background is very difficult due to the properties of the lens. Even on 2.8, my 14-24 wide angle makes pretty sharp backgrounds.
The lens therefore partly determines how much or little depth of field you get.
and what about the third?
If you are close to your subject with your camera and the background is very far away, the background will become a lot blurrier. Are you far from your subject and is your subject close to the background? Then your subject will be sharp and so will your background.
So if you want a very blurred background (called bokeh), grab your telephoto lens, zoom in considerably, open your aperture wide and make sure your background is very far away.
If you want to have everything sharp, take your wide angle (or standard lens if you want less distortion) use a wide aperture and make sure your background is less far away.
Then you use all elements to your advantage.
If you also want to experience this in practice, I would like to invite you to follow this workshop: