Depth of field (DoF) is a powerful creative tool in photography, and by knowing how to take full advantage of it, you will significantly improve your photos.
Almost every photographer knows that you can control DoF by adjusting the aperture. But did you know that several other factors influence DoF, too?
If you want to learn everything about the DoF, keep reading this article.
Depth of field definition
Depth of field in photography is the distance between the nearest and the farthest objects that are in acceptable focus in an image.
Everything that is outside the depth of field we consider blurred or out of focus.
Depth of field depends on aperture, focal length, distance to subject, and the acceptable circle of confusion size.
We distinguish between a shallow and a deep depth of field (also small and large). Shallow depth of field refers to a short distance between the nearest and the farthest objects that are in focus, in contrast, deep depth of field refers to a long distance between the objects.
Factors affecting depth of field
Four main factors affect the depth of field: aperture (f-number), the focal length of the lens, distance from the subject, and sensor size.
The DoF can be calculated by aperture, distance to subject, focal length, and the circle of confusion with the following equation:
for a given aperture (A), circle of confusion (c), distance to subject (d), and focal length (f).
Depth of field and aperture
Aperture is an opening in a lens that light passes through to reach the sensor. The size of the aperture controls the amount of light that falls on the sensor.
The easiest way to control the depth of field is by using the aperture of your lens.
Large aperture = Small f-number = Shallow depth of field
Small aperture = Large f-number = Deep depth of field
It might take you a while to internalize this concept, but once you do it will serve you well in photography. To reiterate, the lower your f-number, the shallower your depth of field. The higher your f-number, the deeper your depth of field.
For example, using a setting f/1.8 will produce a very shallow DoF, while f/22 will produce a large DoF.
Depth of field and focal length
Increasing the focal length reduces the depth of field.
Focal length is a property that describes how much an image of an object is magnified by lens. Longer focal length leads to higher magnification (or zoom) and a narrower angle of view, on the other hand, shorter focal length means lower magnification and wider angle of view.
Depth of field and distance
The closer your camera is to your subject, the smaller your depth of field will be; conversely, the farther you place your camera from your subject, the larger the depth of field.
This effect is exceptionally problematic in macro photography, where the goal is to get as close as possible while maintaining a large DoF.
Depth of field and sensor size
Decreasing the sensor size will decrease the DoF by the crop factor, meaning that by using a 1.6x crop APS-C sensor the resulting DoF will be 1.6x smaller than as if the photo was taken with a full-frame camera.
For this reason, full-frame cameras are used for portrait photography, where shallow DoF creates bokeh. On the other hand, macro photographers can take full advantage of the increased DoF and additional zoom smaller sensor provides.
Circle of confusion
In photography, the circle of confusion is a spot that is produced by a point and is no longer considered sharp. The size of the circle of confusion determines the depth of field.
I know, this was a mouthful.
To simplify, imagine you’re taking a photo of a dot. When it’s in focus, it looks exactly the same in the image and real life. As you turn the focus ring, it starts falling out of focus and becomes blurry (unsharp). When you no longer consider it acceptably sharp, you measure its diameter – and the diameter is the circle of confusion.
The general consensus in photography defines the circle of confusion such that when enlarged to a standard 8×10 inch print and observed from a distance of 1 foot would go unnoticed.
The circle of confusion only sets a boundary between sharp and unsharp. After that point, an effect called bokeh appears.
Let’s get right into it.
What is bokeh?
The term bokeh comes from the Japanese word boke, which means blur and that’s exactly what it is.
In photography, bokeh is a blur produced by the out-of-focus part of an image.
Bokeh can be classified as either good or bad. While the quality of the bokeh is difficult to quantify, it’s usually related to lens quality and price.
Good looking bokeh is very important in portrait, macro, and wildlife photography.
In reality, bokeh is just a huge circle of confusion. However, it’s worth noting, that circle of confusion is not a circle – it’s a polygon that has the same amount of sides as the lens it was taken with has blades.
What is the hyperfocal distance?
Beyond hyperfocal distance, everything can be brought into an acceptable focus.
In other words, the hyperfocal distance is the minimal distance at which you can focus to keep everything beyond it to infinity (in photography: background) reasonably sharp.
The easiest way to determine the optimal focusing distance is by experimenting. Focus onto the most distant object in your scene and then slowly adjusting the focusing distance as close as possible while keeping the background acceptably sharp.
Depth of field and teleconverters
A teleconverter is an accessory lens that you mount between the lens and the camera to enlarge the central part of an image. A downside to using a teleconverter is a reduced amount of light that reaches the sensor.
Regarding the DoF, using a teleconverter has the same results as if you used another lens that would give you the same focal length as the lens + the teleconverter.
For example, if you use a 2x converter on a 50mm lens, it’s the same as if you use a 100mm lens (2×50mm=100mm).
How can I get a shallow depth of field?
To get a shallow DoF, you should use the largest aperture available (the lowest f-number, f/1.8 or lower), a full-frame camera, short focal lengths, and position yourself close to the subject.
Shallow DoF will also create a bokeh, which improves with a better lens.
How can I get a large depth of field?
In contrast to what we’ve learnt with the shallow depth of field, to get a large (or deep) depth of field, you should use small apertures (high f-number, f/22 or higher), a crop sensor camera, long focal lengths; you can even couple your lens with a teleconverter, and position yourself far away from the object.
Depth of field calculator
DoF calculator will help you assess what camera settings are required to achieve a desired level of sharpness.
Depth of field chart
This chart is the fastest way to have your DoF calculations done.
If I were you, I wouldn’t obsess too much about the actual size of the DoF. To be fair; I never even calculated the DoF. Pulling out your phone in the middle of your photoshoot and calculating the DoF might ruin the whole experience for you.
It’s enough that you know what factors affect the DoF. To summarize;
To increase the depth of field:
- Narrow your aperture (larger f-number)
- Move farther from the subject
- Shorten focal length
To decrease depth of field:
- Widen your aperture (smaller f-number)
- Move closer to the subject
- Lengthen your focal length
Feel free to open a discussion with more tips in the comments.
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