Complex sentence: Mayer and Gruber had both developed devices for viewing stereo images, but Gruber had made up a stereo imaging rig out of two Kodak Bantam Specials mounted together on a tripod.
Split into simpler sentences: Mayer and Gruber had both developed devices for viewing stereo images. But Gruber had made up a stereo imaging rig out of two Kodak Bantam Specials mounted together on a tripod.