When it comes to depth of field, we all immediately shout: aperture. After all, aperture simply determines the depth of field... or is it slightly different? Because why is one photo at aperture f4 different 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 and behind your focus point becomes sharper (how many cm or m) is called depth of field. With little 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 center, 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 vague).
You can adjust the depth of field with the aperture. A small aperture (large number such as f11 or f18) ensures a large depth of field, so everything is sharp.
A large aperture (small number such as 2, 2.8 or 4) ensures little depth of field, so a blurred background.
But still you 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?
In fact, the aperture controls only 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 ones are?
If you use a telephoto lens, you will have much less depth of field. A telephoto lens has the property that the background often becomes blurred. Shooting a portrait with a telephoto lens with a very sharp background? That will be a challenge. But especially 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.
Do you use a wide angle lens? Then everything is almost always sharp. A blurred background is very difficult due to the properties of the lens. Even at 2.8, my 14-24 wide angle makes pretty sharp backgrounds.
The lens therefore also determines how much or little depth of field you get.
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 more blurred. 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 a lot, open your aperture wide and make sure your background is very far away.
If you want everything sharp, grab your wide angle (or standard lens if you want less distortion) use a large 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: