Aligning pitch for measurements of the shape of captive bubbles.

The first step required for the determination of surface tension from the shape of a captive bubble is the correct alignment of both the solid support against which the bubble floats and the camera used to record its profile. The solid support should be perpendicular to the gravitationally vertical axis. The camera used to visualize the bubble must be aligned to its axis of symmetry. Alignment of roll for both the camera and solid support is straightforward. For well-collimated light, yaw is unimportant. We show here how to align pitch, first adjusting the camera relative to the gravitational vertical, and then adjusting an agarose dome used as a ceiling above captive bubbles within the visual frame of reference.