Understanding Depth of Field

What is Depth of Field?

The depth of field is the area that lies in front of and behind the subject, which appears to be in focus. In simple language, when you set the focus on a particular subject, there is some area in front and behind the subject that is acceptably sharp and in focus. This area which appears to be in focus is known as the depth of field.

A photo with shallow depth of field will have a narrow area in front and behind the subject which will be in focus, which means the background and the foreground will have more of blurry effect. Similarly, a photo with deep depth of field will have a wide area in front and behind the subject which will be in focus, which means that the background and the foreground will have less of blurry effect and will appear in focus.

Example of shallow depth of field:

Example of deep depth of field:

What are the factors affecting Depth of Field?

You must have heard a lot that the depth of field is controlled by changing the aperture f-stop value, which is true. But this is not the only factor which controls the depth of field, in total, there are three factors affecting depth of field:

a. Aperture f-stop value

b. The Focal length of the lens

c. Camera-to-subject distance

How does aperture affect the Depth of Field?

Aperture is one of the most-known factors which controls the depth of field. The easiest way to understand this is, the lesser the aperture value, the shallower will be the depth of field which is ideal if you need to create blur effect in portraits and macro photography. Similarly, the higher the aperture value, the deeper would be the depth of field which can be used for landscape and cityscape photography to get the maximum area in focus.

The smaller the f-stop number = the bigger will be the aperture opening = the shallower the depth of field (more blur effect)
The higher the f-stop number = the smaller will be the aperture opening = the deeper the depth of field (less blur effect)

NOTE: Changing the aperture value will also affect the shutter speed. Reducing the aperture value will increase the shutter speed and increasing the aperture value will decrease the shutter speed.

Also read: Why f/22 Does Not Produces Sharpest Landscape Photos

How does focal length affect the Depth of Field?

As we all know, using a longer focal length lets us go closer to the subject, and using a shorter focal length lets us capture wider frame. This is not the only use of using different focal lengths.

By using a longer focal length, you can reduce the depth of field and achieve bokeh in the background as well as the foreground. Similarly, when you use a shorter focal length you can increase the depth of field in order to get more of the foreground and background in focus.

Example: This approach can be used in a situation when you want deep depth of field, but you do not want to increase the aperture value as the shutter speed will decrease. What you can do is use a wider focal length in order to increase the area which is in focus in front and behind the subject.

How does camera-to-subject distance affect the Depth of Field?

Camera-to-subject distance is basically the distance between your camera and the subject on which you would be locking the focus on. The closer your take your camera to the subject, the area in focus in front and behind the subject will keep on reducing, thus resulting in shallower depth of field. When you take your camera farther from the subject, the area in focus in front and behind the subject will keep on increasing, resulting is deeper depth of field.

This approach can be ideal when you are using the kit lens (18-55mm f/3.5-5.6) on 55mm to click a flower and the minimum aperture value you can use is f/5.6. As you can not use a smaller aperture value, in order to get shallower depth of field you can move closer to the flower. This will help you isolate the flower from the background and achieve more bokeh.

If you want to click a photo of a group of friends, some standing ahead and some behind each other, simply move away from them and click the photo. This will help you increase the depth of field and all of them would be in focus.

Example: As you can see in the images below, the photo which has been clicked from as closer distance has shallower depth of field as compared to the photo clicked from distance.

Conclusion:

Is the distance of depth of field the same in front and behind the focus point?

The distribution of depth of field is such that it is one-third in front of the focus point and two-thirds behind. The ratio starts changing the moment you increase the focal length and at one point the distribution of depth of field becomes half in front and half behind the focus point.

This is one of the reasons that when you click photos using a wide-angle lens, you get more depth of field behind the focus point and as you increase the focal length the background starts getting out of focus.

Did you know there is a certain distance at which when the focus point is set, you get almost everything in foreground and background well in focus. This distance is known as the Hyperfocal Distance.

Situation : You can not increase the aperture value because of slow shutter speed

As we know, the shutter speed decreases when we increase the aperture value. Suppose you want to click a landscape with deep depth of field and you plan to increase the aperture value, as a result, your shutter speed will decrease. Slow shutter speed will also introduce two things:

a. Moving elements in the frame will introduce trails.

b. Camera shake, if you are clicking handheld.

The alternate approach to get deep depth field would be to not increase the aperture value, instead, move back from the focus point and then click. In case there is not enough space to move back, use a wider lens to capture deep depth of field instead of increasing the aperture value. These approaches would help you click photos handheld with deep depth of field.