Depth of Field
The amount of
a picture from front to back that’s in focus is called its “depth
of field”. If only one part of
the photo is in focus (e.g. the foreground but not the background, or
vice-versa), that’s a “shallow”
depth of field. If both the
foreground and background are in focus, that’s a deep depth of field. Wider apertures
(small F-stops like 2.8) give shallower depth of field, while narrow apertures
(F-16 or F-22) give the greatest depth of field.
Here’s my
friend the Smooth Green Snake demonstrating both Shallow and Deep Depth of
Field:
|
Snake: Aerial View
of the Depth of Field |
Snake: Shallow and
Deep Depth of Field |
|
|
SHALLOW Depth of Field: From front to back, only a small
amount of the picture is in focus, centered around the focal point:
|
|
DEEP Depth of Field – most of the picture from
front to back is in focus |
|
|
|
|
Here’s the same picture shot shot with a wide aperture = shallow depth of field,
and a narrow aperture = deep depth of
field:
|
Sumach Leaves – SHALLOW Depth of Field |
Sumach Leaves – DEEP
Depth of Field |
|
|
|
|
Wide aperture ( F/4) |
Narrow Aperture (F/16) |
|
Fast shutter ( 1/500th second) |
Slow Shutter ( 1/30th second) |
|
Foreground in focus, background blurred |
Foreground and background both in focus |
Elmo Shows Us His
Depth…
|
Depth
of Field |
Shallow |
Shallow |
Deep |
Medium |
|
What’s
In Focus |
foreground in focus |
background in focus |
foreground in focus, background almost in focus (focused on Elmo) |
foreground in focus, background partially in focus (focused on Elmo) |
|
F-Stop |
F-1.8 (wide aperture) |
F-1.8 (wide aperture) |
F-22 (narrow aperture) |
F-8 (medium aperture) |
|
|
|
|
|
|
|
Focal
Distance |
0.5 m |
10 m |
0.5 m |
0.5 m |
|
|
|
|
|
|
|
Comments |
Good if you only want the viewer to notice Elmo’s face – no distracting background |
Not good – background obscured and foreground out of focus. You have to be careful what you’re focussing on if you use a wide aperture. |
Good if you want to show both a foreground subject and the background too. Focussing a bit further out, maybe at 2 m, would have sharpened the background and still left Elmo in focus. |
Good for showing the foreground with a little background for context. |
If you notice the F-stops used in the photos above, you’ll see that a wider aperture (small F-stop, like 2.8) gives a shallower depth of field. The smaller the physical aperture, the more depth of field, and the less you have to worry about focusing. So if you want much of your photo as possible to be in focus, choose a high F-stop (small aperture) like 16 or 22.
What’s a common
problem that happens with shallow depth of field? You have to be careful what you focus
on, because only a narrow part of the picture will be in focus!
|
|
|
|
The photographer has accidentally focused on the background. |
Focus on the foreground, where it was intended! |
So why not just use
very small apertures all the time, so everything is more in focus?
- Smaller aperture means less light – maybe not enough to properly expose, or requiring too slow a shutter speed
- Sometimes you want the background (or foreground) to be out of focus, so it doesn’t distract as much from your primary subject. This is also called “soft focus”, and is used sometimes in portrait photography to give a soft fuzzy effect to an otherwise harsh face.
This picture, shot at F2.8, gives emphasis to the leaf and raindrops since the background is a soft blur due to the shallow depth of field.
