Mirrors with angles
As soon as the mirrors are no longer parallel, rotational patterns appear.
Here you can alter the angle between two mirrors and watch the copies
of Dr. Stickler.
Only for certain angles one will get a "sharp" image. These are exactly
the integer divisors of 180°, i.e.
180°, 90°, 60°, 45°, 36°, 30°,... (test them!).
Here are a few photographs of real world experiments done with real mirrors.