Depth of Field explained by Steve Cushing Photography

Depth of Field

Please read the section on how lenses work first. LINK here to this section.

A basic definition of depth of field is: the zone of acceptable sharpness within a photo that will appear in focus. In every picture there is a certain area of your image in front of, and behind the subject that will appear in focus. Controlling the depth of field controls how much of your image will be in focus. Adjusting aperture controls the depth of field which how much of your image will be in focus.

So depth of field is the area of sharpness within a photo that will appear in focus. The lower the aperture f-stop the smaller the depth of field F-stops 1.2 1.4, 1.6, 1.8 can all be used to reduce the focal depth and create what is called BOKEH (Click for more information).

A deep depth of field means that almost everything in your image will be in sharp focus, from things in the near foreground to things in the far background. Think of a basic phone camera, where everything in the image is sharp and in focus, even things that are far in the distance.

We use a narrow aperture to achieve a deep depth of field when photographing wide vistas, like landscapes and city skylines, where you want everything to be in focus.

A shallow depth of field (as shown in the image) means only the subject will be in focus and the rest of the image will be out of focus. We use a large aperture to achieve a shallow depth of field when photographing a portrait against a busy background, so the person will be in focus and the background will be blurred to not distract the viewer.

If the lens if fixed to the camera the depth of field is constant across the width of the image. We can distort this by shifting the lens (tilt shifting) or by using a rubber mount. See Creative Techniques

Large aperture = Small f-number = Shallow (small) depth of field
Small aperture = Larger f-number = Deeper (larger) depth of field

It may be easier to remember this simple concept: The lower your f-number, the smaller your depth of field. Likewise, the higher your f-number, the larger your depth of field. For example, using a setting of f/1.2 will produce a very shallow depth of field while f/11 will produce a deeper DoF.

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This video is a good explanation of how depth of field works,

Another good video on the subject.

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WHAT IS FOCAL PLANE?

Despite what the name suggests, the focal plane, or the sharpest plane of focus in an image is not the only part of an image that actually appears to be in focus.

Although the points adjacent to the focal plane are not in perfect focus, the brain registers them as being in focus if they lie within a certain range.

The definition of focal plane is the distance from the camera at which the sharpest focus is attained. Picture yourself in a field with a tree far off in the background and add a tape measure under your feet facing towards and away from the camera.

Focus the camera upon you standing on the tape. You will then be in focus, even at f1.2. Now, if you step forwards, or backwards on the tape, you will be out of focus because they stepped out of the “focal plane” (i.e. your piece of imaginary tape).

At f1.2 your distance in focus is very thin. The higher you take your f-stop the more you can move forward or backwards.

You also need to be aware of where you are in relation to the subjects. When using a low f-stop you need to remain directly in front of your subjects… you can’t wonder off 8 feet to the left. You need to be centered and head on to your subject.

Here’s a quick guide on how you can deepen and reduce the depth of field:

Deep depth of field = Large f-stop (small aperture) + slow shutter speed
Shallow depth of field = Small f-stop (large aperture) + fast shutter speed

See also "Why does the aperture not cause vignetting when it gets smaller?" in the Aperture section HERE

SEE ALSO FLANGE DISTANCE

LOOKING AT IMAGES ON THIS SITE

You can see how I use this aspect in photography to add creative effects on this site.

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Steve Cushing Impresionist Fine Art Photography

Embracing imperfection, recording emotions, one impression at a time…