What does small depth of field mean?

Question

Can anyone clarify for me the various terms used to describe depth of field? There are so many it's hard without a photo dictionary to relate in my head what's actually being said to me about the matter...

As I understand it here are the two extremes:

1. what terms are used for no depth of field images (where everything is in perfect focus)?

2. what terms are used for super small depth of field (where the nose is in focus and ears are blurry, background blurry and some foreground if present is blurry)?

And what lens settings are used to obtain these two effects?

Answer 1

• The focus distance is the distance from your camera's sensor in which everything is in perfect focus. Unless you use a specialized tilt/shift lens, there is only one such distance.

• Objects closer and further than the focus distance are out of focus by some amount. The closer to the focus distance, the more in focus they are.

• Depth-of-field is the range of distances where things are acceptably close to being in focus. This is not absolute and is inversely proportional to viewing size. In other words, the same photo has more depth-of-field when printed smaller.

• Shallow depth-of-field means the depth-of-field is small which implies that things get quickly out of focus. Depth-of-field is made shallower using larger apertures (denoted by small F/numbers), using a longer focal-length (more zoomed-in) and using a larger sensor (For example, full-frame vs cropped vs compact-camera sensors).

• The Hyperfocal distance is the distance at which you can focus your lens to make things acceptably focused at infinity while maximizing depth-of-field. This short article explains it and includes a calculator to compute the hyperfocal distance depending on your camera and lens.

Answer 2

Depth of field refers the range of distances at which objects are acceptably sharp. To answer your questions:

1. When everything is in focus there is still a "depth of field", thus they're not "no depth of field" images, it's just that the depth of field is very large. I know of no term other than "large" or "infinite" depth of field to describe such images.

2. From the definition of depth of field it follows that "small depth of field" means small range of sharp objects. This is also referred to as shallow depth of field (the term Bokeh is often thrown around in relation to such images however that word refers to the quality, not quantity of the out of focus areas).

It irks me a little when I see people post comments on flickr like "great DOF", yeah 86.3cm that's a really great depth!

Answer 3

The depth of field is based on the focal length of the lens, and the width of the aperture.

The key thing to think about is that the aperture size is inversely proportional to the depth of field.

Also, keep in mind that a smaller aperture number relates to a larger aperture width. See: What does the f-stop printed on the lens refer to

There is a great calculator available that can help you visualize the depth of field.

Answer 4

For #1, "no depth of field", you actually describe infinite depth of field.

The "field" is the area considered to be acceptably in focus, and the depth is the distance that area covers. (Think "depth" in the sense of a deep closet or deep cabinet, not a deep ocean.)

A perfect pinhole lens gives an infinite depth of field. A completely unfocused blur from an infinitely large aperture is the theoretical opposite.

Answer 5

A quick answer to the lens settings used for this effect, since none of the other answers seem to go into detail about this:

A larger aperture (A smaller F-number) gives a shallower depth of field. Pictures with the eyes in focus and the tip of the nose and ears out of focus are typically shot at F/2.8 or smaller. From F/8 or larger (smaller aperture opening) large objects can be completely in focus.

Answer 6

Rather than a technical answer, here's an example. Note that while the flowers themselves are clear and the small branch at the upper right is clear the branch coming from the upper left is not clear despite not being very far behind the flowers.

This is the result of having a very narrow depth of field--this was taken at 300mm effective and the lens was wide open, IIRC f5.6. As I wasn't carrying a tripod that day it was the best I could do.