Heather Owens Photography Blog » Arkansas Portrait Photographer

LESSON 3

Welcome back, class!

This week, we’re going to cover one of my favorite things to play with in my photography:

So, what exactly is depth of field?  You’ll remember in our inaugural class, I told you that one of the things aperture controls is depth of field.  Practically, depth of field is the portion of an image wherein objects are in focus.  To be technically correct, depth of field is really “the zone of acceptable sharpness,” which includes the areas in front of and behind a focused subject that also appear in focus to the human eye.  I say “appear in focus” because the human eye has a finite ability to see fine detail; therefore, elements that are really out of focus still appear sharp.  Thus, when you focus on an object, in reality, only that object is in focus, along with any other objects in the scene that are exactly the same distance away from the camera.

Everything else—that is, all objects on other focal planes—will be out of focus to some degree, whether it is perceived by the human eye or not.  How much out of focus everything else is depends on something called “the circle of confusion.”   I’m not even going to get into this one because it’s even worse than the name suggests.  A diagram of the concept looks something like this:

And, the formulas for calculating the circle look something like this:

I can see your eyes glazing over.  But don’t fret, the good news is that  you don’t have to know what any of this means to be able to use and manipulate depth of field in your photographs (and, the crowd goes wild!).  The fact that you even know the circle of confusion exists makes you pretty bad-ass.  Pat yourself on the back for even reading this part.  Or, go get a candy bar.

Now, back to the important stuff.  In simple terms, depth of field is a phrase used to describe what is inside the focused area of your image and what is left outside the focused area.  And, that, my friends, is all you really need to know.

There are 3 ways to control depth of field:  aperture, distance, and focal length.

CONTROLLING DEPTH OF FIELD WITH APERTURE

The variable that has the biggest impact on depth of field is aperture.  (Remember, aperture is simply the  size of the opening that allows light to go through the lens on your camera.)  Bigger apertures (the smallest numbers) equal shallower depths of field.  If you have a large/wide aperture (like f/1.8), you will only have a very narrow location in your image that is focused . . . a shallow depth of field.

In this image, I used a large aperture (f/1.8), so the only thing in focus is the object I actually focused on—the first pear.  Everything else is out of focus, even though the distance between the first pear in the line and the last is only about 18 inches.  This is a very shallow depth of field.

In contrast, if you set your aperture to a small value (the biggest numbers, like f/22), your focused area will be larger.

In this image, you can see that almost everything in the scene is in focus—even the leaves on the plant behind the pears.  The only thing that changed between the two images is the aperture.  The first image was shot at f/1.8, while the second was shot at f/8.

PUTTING APERTURE INTO PRACTICE

If you want only the object the camera focuses on to be sharp with everything else out of focus—such as a portrait of one individual with the nicely blurred background—then you would “open up the aperture” (i.e., use a large aperture).

When you shoot wide open, you can get some pretty amazing shots:

On the other hand, if you need most of your image to be in focus—such as in a portrait with 2 or more people or in a landscape—then you would “stop down” the aperture (i.e., use a smaller aperture).

In this image, I needed to use a smaller aperture because the people were not all on the same focal plane.  If I had used a really large aperture, someone would have been blurry!

Here’s a little cheat sheet about aperture and depth of field for you to use:

CONTROLLING DEPTH OF FIELD WITH DISTANCE

In addition to aperture, another way to control the depth of field in your images is by changing the distance between the subject and the camera.  When you focus on a subject that is close to the camera, the depth of field is more shallow than when you focus on a subject farther away from the camera.  So, step away from your subject to obtain a deeper depth of field, or move in closer to get a more shallow depth of field.

CONTROLLING DEPTH OF FIELD WITH FOCAL LENGTH

You can also use focal length to affect the depth of field by using a zoom lens instead of a wide-angle lens.  If you photograph your subject with a wide-angle lens, the emphasis of the image is usually not on the subject.  This makes more of the scene appear to be in focus.  However, if you zoom in on your subject and fill the frame with the subject’s head and face, the subject will dominate the image.  The other objects in the scene will lose importance and appear out of focus.  Thus, a wide-angle lens will generally have a greater depth of field than telephoto lens.

I know what you’re thinking now . . . what’s the difference between physically getting closer to your subject by walking up to it and virtually getting closer by zooming??  The difference is in the “look” of the image.  It is said that using a long lens (i.e., a lens with a long focal length or zoom), as opposed to a fixed-focal length (or prime) lens, provides a “flattened” perspective, which makes the shallow depth of field more prominent than what you get by just walking closer to the subject.  Try manipulating the depth of field both ways and see what you think.  I, for one, prefer shooting with primes.

BOKEH

The thing I love most about shooting with a very shallow depth of field is bokeh.  Bo-what?!?!  Bokeh.  Bokeh is a term that describes the rendition of out-of-focus light in an image.  It occurs when the lens creates soft-edge circles of light in the blurry areas.  The term comes from the Japanese word “boke,” which means fuzziness or dizziness, and it describes the appearance, feel, and character of whatever blur is present in an image.  You can create bokeh in your images by manipulating the depth of field.

I hope this has given you a little insight on depth of field and a little more insight on aperture.  Next week, I’ll talk a little more about shutter speed and stopping motion in your images.

Class dismissed.

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