What device automatically operates a camera's shutter to ensure correct exposure based on the speed of the airplane?

The intervalometer is the correct answer because it is a device designed to automatically control the timing of a camera's shutter release. In the context of aerial photography, where speed and lighting conditions can vary considerably, the intervalometer can adjust the exposure time to ensure that each photograph is properly exposed. This is particularly important when capturing images from an airplane, where factors such as altitude and speed can affect the amount of light reaching the camera sensor. By automating the shutter operation, the intervalometer allows for consistent and high-quality images regardless of changes in flight conditions.

The other options do not serve the same function. A yaw angle meter measures the rotational position of an aircraft on the vertical axis, which is unrelated to camera operation. A collimator is used to align and focus light beams, often in optical instruments, but it does not directly relate to the timing of a camera's shutter. A diapositive refers to a transparency used for projection and is not a device that manages exposure settings in a camera. Thus, the intervalometer's specific role in managing shutter timing makes it the appropriate choice for ensuring correct exposure in aerial photography.