DIY sliding cardboard periscope

The principle of the periscope is a system of a pair of mirrors mounted at an angle. They were used mainly in military equipment on tanks and submarines in order to protect the observer in them from injury. Our periscope was created more for fun, but it also has practical benefits.

If you make a retractable hobby, like a telescope, you can change its size without losing the main function, because with parallel movement, the mirrors will not change their angle.