Depth of Field

In the previous chapter on the benefits of manual focus, James mentioned how the amount of light you have as well as how much your zoomed into your subject, will effect how hard or easy it is to focus.

This has to do with a concept called depth of field.

Depth of field describes how deep your focus will be. In other words it’s a term that describes how many objects will remain in focus in your frame at one focus setting.

If you have a large depth of field that means that more objects at various distances from your camera are in focus.

In this case we’re wondering how many of these hurdles can remain in focus without having to change the focus ring during the shot.

The first factor that effects depth of field is the amount of light you have.

Here it’s a bright sunny day, we have a lot of light so it’s easy to keep things in focus.
Even if we move the focus ring most of the hurdles stay in focus.
So here we have a great depth of field, but now it’s the end of the day and we don’t have much light left therefore we don’t have as much depth of field.
As you can see not as many of the hurdles are in focus now and as the runner runs we have to adjust the focus ring to keep them in focus.
To reiterate in this shot less of the hurdles are in focus because we’re zoomed in, we’re at a long focal length and if we zoomed out more of the hurdles would be in focus at one time.

“Welcome back” “Over here” “Now in addition to light the other important factor effecting depth of field is focal length.”

Now with most consumer grade digital cameras, you don’t have to worry to much about focal length because they already come with a zoom lens, to make your lens telephoto or long you simply zoom into your subject.

Now zoomed into me like we are here is the equivalent of a long focal length. Generally speaking there’s less depth of field and fewer objects are in focus in this shot. Now if we zoom out to a wider angle shot of me that’s the equivalent of a short focal length or short lens. In this shot there’s more depth of field and there are more objects in focus in the frame.

To review, when you’re zoomed in it’s hard to focus and when your zoomed out it’s easy to focus, and that covers the basics of depth of field.

It depends on the amount of light you have and what your focal length is.

If you know your depth of field you will know how attentive or inattentive you have to be when focusing your camera.

DEPTH OF FIELD MEANS…

The number of objects “in-focus” in the frame
The area of the frame that is “in-focus”

FACTORS THAT EFFECT DEPTH OF FIELD ARE…

The amount of light entering the lens
“F-Stop” and “Shutter Speed” both effect the amount of light in your image
The focal length or “how far you are zoomed in or out”

Depth of Field…
Will bring attention to your subject in the frame once you master the technique!

REDUCING DEPTH OF FIELD

Now we’re going to get a little more advanced, the lens on camcorders have become so good that sometimes, to many things are in focus in a frame.

Here for example maybe we want the runner to be in focus but not all the hurdles, so we need to reduce our depth of field.

In order to reduce our depth of field we need to open up our iris all the way. The lower the F-stop number, the more open the iris.

But first we pop on some neutral density filters to darken the image. Which forces us to open up the iris in order to compensate.

HOW TO REDUCE DEPTH OF FIELD

Zoom in the area you want in the frame
Apply neutral density filtering
Open the iris all the way to highest F-stop you can to get the proper exposure

HOW DOES THIS ACCOMPLISH REDUCING DEPTH OF FIELD?

Applying neutral density filtering reduces the amount of light coming into the lens
Then opening the iris brings the light levels back up to get the correct exposure

The lower the F-stop the narrower the depth of field!

With the iris opened up all the way our depth of field has finally been reduced.

Now we’re just focusing on the runner and the other hurdles are out of focus.

Manipulating your depth of field … will take a little practice!

Practice ……..until you get it right.