How do I blur the background in my photos?

One technique every photographer must have at their disposal is the ability to blur the background in their photos. When you blur a photo background but leave the main subject in sharp focus it helps to emphasise the subject. It also helps prevent the photo background from distracting the viewer. This article explains how you can control and blur your photos background.

How do I blur a photo background like this

How do I blur a photo background like this

The Aperture

The aperture is the opening found in a camera lens that enables light to reach the sensor or film. The primary use of the aperture is to control exposure. When you use a wide aperture more light passes to the camera sensor compared to using a small aperture.

The secondary use for the aperture is to control something known as the depth of field. This sounds complicated but it’s really not. When you take a photograph the camera will focus on a point in the scene you are photographing. Objects in the photograph that are either nearer to or further away from the camera than the point of focus become blurred and out of focus. The depth of field in the image is the area in front and behind the point of focus where objects still appear to be in focus.

If you use a wide aperture when taking a photograph the depth of field is shallow. This makes objects away from the point of focus appear more blurred than if a small aperture is used. As we use progressively smaller apertures the depth of field will increase. Therefore taking a photo using a wide aperture such as f/1.8 will give a much shallower depth of field than a small aperture such as f/16.

If you want to blur the background in your photos use a wide aperture, typically f/2.8 or wider.

How aperture controls the amount of light in photography

How aperture controls the amount of light in photography

The Focal Length

Whilst using a wide aperture can help blur a photo background there are other techniques we can use. This is especially useful if your lens has a small maximum aperture. Often cheaper zoom lenses have variable apertures with typical ranges of f/4.5 – f/5.6. More expensive zoom lenses and prime lenses (with a fixed focal length such as 50mm) tend to have wide maximum apertures of f/2.8 or wider.

You can increase the apparent blur in your photos by using a lens with a longer focal length. For example if you shot the same scene with a 24mm lens and a 150mm lens, the background of the photo shot with the 150mm lens would appear more blurred.

To blur a photo background chose a longer focal length lens, typically over 50mm.

Focus Point

The point of focus is also important in determining the depth of field and therefore how blurred the photo background appears. The nearer the point of focus is to the camera, the less the depth of field and therefore more blurred the background.

Don’t allow the camera to automatically pick the point of focus as it may focus on something in the background in which case your subject may become out of focus. As you move the point of focus further away from the camera the depth of field will increase so the blurring effect is less.

If you want to blur your background move closer to the subject you are focussing on.

Sensor Size

You may not be able to do anything about this variable but you should be aware of it. The smaller the sensor size in your camera, the greater the depth of field that will be created. For example if you shot the same photo using a full frame camera and a compact camera, even using the same focal length, aperture and position, the full frame camera would have far less depth of field than the compact camera. Less depth of field means you can blur the background more easily.

If you have an option and want to blur a photo background, use a camera with a larger format sensor.

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