The depth of field of a camera defines the depth range to be covered by the camera. In 3D images, the resolvable depth range is also determined by the depth of field (DOF). Hence the depth resolution and resolvable number of depth layers obtainable with a given 3D display will be defined within the DOF when the display has the same resolution as the total camera resolution of the array in the horizontal direction. The depth resolution and resolvable number of depth layers are mathematically derived in terms of the circle of confusion. The resolvable number of depth layers is approximately linearly proportional to the camera distance and inversely proportional to the aperture diameter of the camera objective. The accuracies of the derivations are examined experimentally. The results show that the DOF extends slightly and the depth resolution improves up to 20% more than that predicted by theory for the given experimental condition. This means that the depth resolution derived has more than 80% accuracy.