Disclosed herein is a method and apparatus for videoconferencing that allows video images from two or more cameras at the same site to be displayed as a single panoramic image. Each of the Fresnel lenses is continuously alined with the sun during a desired period of operation and are maintained at a focus distance from energy absorbers by the support frames and the solar tracking drive. The circular sealing lip is provided so as to form a waveform having concavity and convexity curving in the drive direction of the main valve, due to a thermo-sensitive movable body.