Depth of Field--A Different View
Many photographers have a very limited understanding of depth of field. That understanding is often limited to the notion that larger apertures (smaller aperture numbers) are associated with a small depth of field. That's useful to clean up distracting backgrounds but there's more the action photographer should know. The focal length of the lens has a huge role in determining the depth of field and that fact is both useful and often unappreciated.
First, let's consider the typical situation, long focal length (300mm) and large (f/2.8) aperture. Here the combination produces a creamy background that makes the player pop off the page.
But what if you want the other effect? A large depth of field.
This is exactly the situation I was in two weeks ago. My goal was to capture basketball players on the court and include the overhead scoreboard. Both needed to be in focus. My mentor Mike 'Chico' LaBarbera was visiting from Eau Claire, Wisconsin and he was using my 1D X and the 70-200mm f/2.8 IS II. That left me using the 1D IV with a 24-70mm f/2.8 II. My buddy Mark Weaver had strobe lights set up but wasn't using them for this tournament game. This gave me control over the two key factors--Aperture and Focal Length. The first thing I did was to zoom to the wide (short focal length) end of the lens, 24mm. Then because I was using the stobes, a small aperture was chosen, f/8.0, with only a modest increase in ISO to 640. I pre-focused on the backboard, about 12 feet away.
Small apertures and short focal lengths = large Depth Of Field. So, how large is that DOF?
There is a handy DOF calculator on the internet.
Plugging in the values of 1D Mark IV, 24mm, f/8.0, and 12 feet yielded the DOF.
Everything from five and a half feet to infinity was going to be in focus!
Because the DOF was going to be quite large, I modified my technique to take advantage. I always use back button focus so once I pre-focused on the back board, I just avoided the back button and my focus would remain fixed at about 12 feet. There was no need to worry about focusing because everything was going to be in focus. The camera was set on the ground for visual effect and because the focal length was so wide, aiming merely consisted of pointing the camera toward the area of action with a slight upward tilt. No looking through the viewfinder. No focus tracking. Just rough aiming 'from the hip'. Not even from the hip since the camera was literally on the ground.
Here is the result.
The Garden City Buffaloes beat the defense downcourt and seal the win.
How far can you take these principles? Well, if you want to show three wrestlers and the arena where the state championships are held, you can shoot at 12mm (fisheye) and f/5.0 from 5 feet to get a DOF that extends from 27 inches to infinity. The arena, the crowd and these three top wrestlers are all part of the story.
Let's take a closer look at the role of the lens focal length in depth of field. Consider the case where a photographer is using a Canon 7D to photograph sports and that he is at f/8.0 at a distance of 12 feet. I've been alluding to the fact that focal length is important in calculating DOF. Let's check the DOF at 24mm and at 200mm under those conditions.
24mm focal length DOF = 286 Feet From 6 ft to 292 ft.
200mm focal length DOF = 4 Inches! Just 12 feet +/- 2 inches
Consider focal length before aperture as you plan your depth of field.
Put the depth of field calculator and the principles of DOF to work in your images for your purposes. The focal length of the lens is a key aspect of that calculation.
PS Don't forget that you can often pre-focus and shoot "From the Hip" when necessary at those wide focal lengths! Think of how you might use this DOF information with a wide angle remote during the upcoming track season to obtain a memorable shot that average shooters won't think to get.
Philip S. Zivnuska