How to control Depth of Field in Photography

It is one of those things that give you great control over the atmosphere of the image. Depth of field really determines what kind of images we are looking it. From shallow depths of field to those all around sharp images, aperture on our cameras really controls what we show and what others can see.

What is depth of field?

A camera can only focus its lens at a single point, but there will be an area that stretches in front of and behind this focus point that still appears sharp. This zone is known as the depth of field. It’s not a fixed distance, it changes in size and can be described as either ‘shallow’ (where only a narrow zone appears sharp, the rest is blurry) or deep (where more of the picture appears sharp).

Why do I need to know about it?

Because depth of field has an impact on both the aesthetic and technical quality of a picture sometimes you’ll want to use an extensive depth of field in order to keep everything sharp. A classic example is when you’re photographing a landscape, where generally the most desirable outcome is to capture detail from the foreground to the horizon. Other times, a shallow depth of field will be preferable. It enables you to blur background and foreground details, causing distractions to melt away and allowing you to direct viewers to the focal point in a picture.

A shallow depth of field is perfect for food photography. It obscures backgrounds and brings out the star of the show!

How to control depth of field on your camera

Many digital cameras come with a Depth of Field Preview button near the lens mount, or enable you to assign the same function to one of the other buttons. However, this doesn’t have any effect on the depth of field. The image you normally see through the viewfinder or on the Live View screen is displayed at the lens’s maximum, or widest, aperture; the aperture you dial in on the camera body will only be set when you take a picture. However, pressing the Depth of Field Preview button allows you to view the scene at the working aperture, so that you can see what areas will appear sharp. There’s a range of ways to control the depth of field – the choice of aperture, focus distance and the type of camera. In a nutshell, wider apertures and closer focusing distances lead to a shallower depth of field.

Pressing the depth of field preview button of your camera can give you an idea, what the image will look like once you press the shutter button

What is Wide and Small Aperture?

Wide or large apertures correspond with the small f-stop numbers available on your camera. So an aperture of f/2.8 is wide (only part of the image is sharp, the rest is blurry), while an aperture of f/22 is small (the whole image would be sharp). Again, focusing distance plays a part on the overall effect, with wide apertures offering considerably more depth of field when focused on a subject far away than they do when focused on a subject that’s close to the lens. However, changing the focusing distance is often the least convenient way to control depth of field, it’s much easier to simply select an alternative aperture setting. The only thing you need to be aware of is that shifting from a large aperture to a small one can lead to blurred photos.

Portraits require a shallow depth of field to bring out the person your are taking the photo of

Type of camera and depth of field

It’s the size of the imaging sensor inside the camera that makes the difference. The larger the sensor, the shallower the depth of field will be at a given aperture. This is because you’ll need to use a longer focal length or be physically closer to a subject in order to achieve the same image size as you get using a camera with a smaller sensor – and remember the effect that focusing closer has on depth of field. This is why a full-frame camera produces a much shallower depth of field than an APS-C SLR or compact system camera (CSC) at equivalent focal lengths and apertures.

Sharp from front to back: a wide depth of field is perfect when it comes to landscapes where each element should be in focus.

Long Lenses and Shallow depth of field

The focal length of the lens does appear to have a significant impact on depth of field, with longer lenses producing much more blur. A 200mm lens focused at 12ft will have a wafer-thin depth of field compared to a 20mm lens focused at 12ft. However, if the subject occupies the same proportion of the frame, the depth of field (the area that appears sharp) is essentially the same whether you’re shooting with a wide-angle lens or a telephoto! You would, of course, have to move closer with a wide lens or further away with a telephoto lens to maintain the same subject size. The reason longer lenses appear to produce a shallower depth of field is thanks to their narrow angle of view: compared to a wide lens, a telephoto will fill the frame with a much smaller area of background, so any blur appears magnified too. Use this characteristic to add a professional sheen to your portraits.

Hopefully these tips will be useful to you and if you have any further questions let me know in the comments below.

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