Gulliver’s Hand An experiment in Perspective and Depth of Field using a Digital Camera

Objectives:  Discover how Depth of Field (DOF) can be manipulated to skew the interpretation of an image  Become familiar with adjustments of Aperture and how those adjustments alter the DOF  Create a Lilliputian object/person for Gulliver to “hold”

Skewing the Perspective  The ability to change perspective can provide for some interesting special effects in digital photography

What appears to be real…  In this picture, the man appears to be holding the “catch of a lifetime”

What is real…  In this picture, we see the truth. How is this illusion created?

Focus Background  In this picture, we see the man is in focus, but the fish is not. Does this make you believe the fish is that large?

Focus Foreground  In this picture, the fish in the foreground is in focus, but the man in the background is not. To the mind’s eye, there is distance between the objects.

Plane of Critical Focus  When an object is sharply focused, adjacent objects the same distance from the lens are also focused. This slice of focus is called the Plane of Critical Focus. There is an area in front and behind this plane where objects are also in focus but to a lesser degree. See

Depth of Field  The near and far limits of depth of field are shown here as two planes (B and C), parallel to the plane of critical focus (A). Actually, they are usually not visible as exactly defined boundaries. Nor can you usually find the plane of critical focus by looking at a picture. Instead, sharp areas imperceptibly merge into unsharp ones. Notice that in the diagram the depth of field is not evenly divided. At normal shooting distances, about one-third of the depth of field is in front of the plane of critical focus (toward the camera), and two- thirds is behind it (away from the camera). When the camera is focused very close to an object, the depth of field becomes more evenly divided.

How the mind sees things  When we view something up close, it appears large to us, from a distance it appears small. Experience tells our mind to compensate for this. When two objects in the distance are focused by our eyes and they exist on the same plane of critical focus, our mind tells us that their proportions relative to each other are correct. They can be compared.

The Magic of 2-D  When we change the aperture on our camera, we change the focal length of the lens which, in turn, increases or decreases the DOF. If the DOF is large enough, we can make objects of different distances from the lens appear to lie on the same plane of focus. This “fools” our mind into thinking their proportions are correct. This can make large objects appear small and small objects large. Hence, the illusion. The trick is to adjust the aperture until both foreground and background objects are in sharp focus.

Assignment:  You are to photograph a large object (person, globe, car, etc.) in the background while your partner holds his/her hand, palm up, in the foreground close to the camera so that it appears to be holding the large object. The camera should be set to either Aperture Priority mode or Manual mode so that you can adjust the aperture until both objects appear in focus  Make a log of your camera settings per trial and adjust those settings according to the output until the picture shows both objects in clear focus. A tripod should be used so that the picture taker can be free to move the partner’s hand to line up the objects.  Switch places and let your partner try this.  Write a short summary about aperture settings and depth of field. Which object is in focus when the aperture is open? Which is in focus with a small aperture?

Examples