DEPTH of FIELD and Lenses

Do Wide Angle Lenses
Really Have Greater Depth of Field
Than Telephotos?

Testing The Theory

Most photographers accept the common belief that short focal length lenses have greater depth of field than do long lenses. A wide angle lens, in other words, will give greater depth of field than will a telephoto. Right? 

Sounds about right, but it's not the case. In fact, if the subject image size remains the same, then at any given aperture all lenses will give the same depth of field.

Because this is such a controversial statement, and because it initially flies in the face of common experience, I have created the following set of example images. 

The set-up for it was as you see below. Camera on a tripod and two light stands holding test subjects — a gremlin, which is the main subject, and a hand puppet the other. A tall tower at infinity is the third.

Each of the frames below was taken so that the gremlin doll is exactly the same size in each frame. I used the camera's circular center focusing spot as a size reference. The gremlin doll just filled the circle. The hand puppet on the foreground light stand is about 3 feet in front of the gremlin, and the tower is a mile or more away.

Focal lengths from a 400mm telephoto down to 17mm ultra-wide were used. The lenses were all set at f/5.6 and the gremlin doll was the point of focus. As you can see there is not enough depth of field at this aperture to have either the hand puppet or the tower in focus. This is what I wanted. Incidentally, I have not bothered to spend too much time correcting and matching the frames for colour balance or levels. DOF is all I'm concerned about illustrating.

The Depth of Field is Essentially The Same

As you can see, the degree to which the tower and the hand puppet are out of focus is essentially identical in each frame regardless of focal length. To be sure, perspective changes dramatically, but not depth of field.

      

400 mm                                                 200 mm   

      

100 mm                                                50 mm   

      

28 mm                                                17 mm

17 mm Enlargement

In the 28mm and 17mm frames the hand puppet is no longer visible, because to keep the gremlin doll the same size I had to get closer than 3 feet — inside the distance to the puppet. But, to show you what I can see in the original images I have blown up the 17mm frame so that you can more clearly see the distant tower. 

Clearly, the degree of unsharpness is indeed the same as in all the other frames — even the one taken with the 400mm lens. Thus the depth of field is the same. If I had been able to set up this test so that the near subject (the hand puppet) was in the frame as well you would see that it too would show the same DOF as all the other frames.

A Final Word

There are those that will no doubt find fault with either my fundamental assertion or with this test. Yes, I know that there are some flaws with both, among them that I am not taking into account diffraction and other second order effects. But, from a practical point of view, what really counts to photographers working in the real world is what ends up on a print in front of them. The fine points of optical theory are one thing, prints hanging on the wall are another. My orientation as a photographer and as a teacher is toward the pragmatic. 

If anyone is dissatisfied with this test or doesn't believe it, I urge you to go out and do your own test. All it takes is several lenses, a roll of film, a few props and a parking lot. Enjoy.