Sometimes the answer to a simple question is more complicated than the answer to a complicated question. Is the focal length of the proposed Periscope critical? As you can see from Gullstrand's Equation the focal length will be slightly less than 500 mm for practical element separation. Will a shutter be used between the elements? What is the required image size? Periscopes have been designed to cover up to 70 degrees at f/30. In primitive cameras, the coverage was less, and the aperture larger. Will the chromatic aberration inherent in the Periscope be a problem? For black & white photography, performance can be improved by color filters. How will you mount the lenses? Some of us are experienced in improvising lenses and lens accessories.