Every time we take a photo we have the opportunity to make the image something special. Photography is an art form where there is no right nor wrong way. Only the way we want the photo to look. One of the ways to create an image just the way we want is by understanding depth of field and using it to control how much of the scene is in focus. This is done using the aperture in the lens. If we want more depth of field we use a smaller aperture. If we want less in focus, use a larger aperture. The larger the aperture the less depth of field. This is why so many photographers buy prime lenses with apertures in the f/1.2 to 1.4 range. This gives a very shallow depth of field so only what the camera focuses on is sharp.
An easy way to control the aperture is using the aperture priority mode on your camera. On a Canon camera it is the AV, Aperture Value, setting on the main dial. If you have a Nikon it is the A, Aperture Priority, on the dial.
In this mode you can choose the f/stop and the camera does all the other settings for you so the exposure is accurate. You can set the aperture in the manual mode as well but you must also set the shutter speed and ISO properly to get a good exposure. I find the semi automatic mode of Aperture Priority to be the most convenient. I can set the aperture to what I want and know that the camera is smart enough do the rest.
Depth of Field
Here are some examples of depth of field. In the first image we used an aperture of f/1.4 and you see that the only thing in focus is the group of three billiard balls in the center of the table.
Now if we close down to the smallest aperture on this lens, f/22, without changing the focus, we see that almost the entire room is now in focus.
If we want to control the depth of field even more, we can use a middle f stop like f/11 and keep the focus to just the balls and not the entire room. We have a great deal of control since we can use any aperture we want.
You will need to keep an eye on the shutter speed when shooting in aperture priority mode. When the lens is stopped down to a smaller opening the shutter speed will get slower in order to keep the exposure accurate.
Scene Modes to Control Aperture
If you don’t have a camera with full controls there are a couple of the scene modes you can use to control the aperture. One mode that will allow you to shoot images with a shallow depth of field is the Portrait mode, usually symbolized by the profile of a girl.
In this mode, no matter what camera you have, the lens will open up to it’s widest aperture when you take the picture. And a wide aperture means less depth of field (less in focus).
When you want to get the most depth of field using a scene mode use the landscape mode. This mode is usually symbolized by a couple of mountain peaks.
In this mode the camera will use the smallest aperture possible. This aperture will vary based on how much light there is. So if you are shooting in low light the camera may not shoot at the smallest aperture.
Well I hope this helps to de-mystify depth of field and make it easier for you to create just the right look in every photo you take.