# What does small depth of field mean?

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?

• 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.

• Just a pedantic note of narrow applicability: Tilt/shift lenses imperfectly mimic the capabilites of view cameras (unless you consider a view camera to be one big t/s lens...), so they, too, have "more than one" focal distance. – RolandTumble Dec 21 '10 at 19:41
• How can a photo have more depth of field when printed smaller? The photo can't magically change itself to have more depth of field... – Nick Bedford Jun 14 '11 at 21:51
• @Nick - DOF is a perceptual phenomenon and, as a correlary of points one and two above, has to do with your ability to perceive the difference in focus around the plane of focus. On a smaller photo, your ability to see that difference diminishes. DOF-calculator either let you specify the circle-of-confusion or use an implicit print size, traditionally an 8"x10" print viewed from 12" away by someone with 20/20 vision. – Itai Jun 14 '11 at 22:13
• I see what you mean. I just tested this with one of my photos. The photo and the depth of field itself is the same, as that cannot physically change once captured, but a larger viewing size makes it easier to perceive the depth of field in the photo. I found myself more aware of the bokeh when holding it close. – Nick Bedford Jun 14 '11 at 22:20
• @Nick - Getting closer but the truth is there is no depth-of-field in an image. Only ONE distance is in focus, everything in front and in back is out of focus but gradually so. How fast you notice things become out of focus depends on the viewing size. That is the depth-of-field. – Itai Jun 14 '11 at 23:52

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!

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.

• It is also based on the size of the recording medium as this affects the way photos are composed (closer focusing distance to fill the frame). – Nick Bedford Jun 14 '11 at 22:30

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.

• If only there was ƒ/0 :-( – Nick Bedford Jun 14 '11 at 22:33