Look at the image in the periscope viewfinder. You can turn the device around its vertical axis. What are you seeing?
How does it work
Thanks to the system of precisely set plane mirrors which reflect light rays, our eyes receive images of places that cannot be seen directly.
Periscopes with more complicated optical systems are used by the military, e.g., in submarines, tanks, armoured cars. Currently, they are being superseded by video cameras .