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Understanding the Factors that Affect Depth of Field

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When we're starting out in photography, understanding depth of field is the one of the first things we try to understand. What we often don't realize is that depth of field is affected by more things than just aperture. In today's tutorial, you'll get some quick tips about the other factors that cause changes in the depth of the field of your images.

What is depth of field (DOF)

The simplest definition for depth of field is the area of your image that is in focus. More specifically, the distance between the nearest and the farthest object that are in focus. The shallowness of  the depth of field depends of the f/stop also known as aperture, the focal length of the lens, the size of the camera sensor and distances between you, the subject and the background.


Aperture or also known as f stop

The first thing we are going to talk is the aperture value. What is aperture? Well, when you look at camera lens you are going to see a maximum aperture range for that lens. For example f/3.5 – 5.6.  The main purpose of the lens is to collect light and deliver it to the camera sensor.

The aperture of a lens is the diameter of its opening. Aperture is expressed as a f/stop. The smaller the f/stop number (or f/value), the larger the lens opening (aperture). Depth of field depends of the size of the opening of the aperture. The larger the aperture opening is the more shallow the depth of field will be and opposite vice versa.


Focal length

The next thing that defines depth of field is focal length. If you have zoom lens or two prime lenses that are different in focal length you can test this yourself. The basic idea is that the longer the focal length is, the shallow the depth of field will get. And of course, the opposite is true when we have short focal lengths. For example if you shoot something with a 50mm lens at f/2.8 and then shoot the same thing with 200mm lens at f/2.8 the difference in the depth of field is going to be dramatic.


Sensor size

Let’s think of a pocket camera. Have you ever noticed that when you shoot with such a camera you almost never get a shallow depth of field and everything is sharp in focus? That's because the sensor of the pocket cameras is so small. But if we take a look at cameras with bigger sensors, for example full frame cameras or with a crop factor of 1.5/1.6, you will see that the depth of field is more shallow. To summarize, a bigger the sensor size allows you to achieve a shallower depth-of-field.


Distance between you and your subject

The closer you are to your subject the shallower your depth of field will be. If you're 2 meters from a subject, shooting at f/2.8 with your 50mm lens, you may get 10cm of depth to your focus. With thensame lens and aperture at 10 meters, you may get 100cm of depth. If you're looking to create soft backgrounds with a less than optimal lens, just get really close to your subject.


Distance between the object and background

The final thing we are going to talk about today is the distance between the object we are shooting and the background. The further away the background is from the subject, the more blurred the background is going to be. For example, if we shoot a model that is standing 3 meters away from us and the background is 5 meters behind the model, the background will be sharper than if the background were further away.

Conclusion

Understand how depth of field works is a crucial part of photography. Being able to choose when to include a background or make blurry and soft allows you have more control over how your images look. If you have good tips for using depth of field or have some images that feature one of these principles, please share them below in the comments!

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