[HenrikB]

I remember connecting a VHS video camera directly to a cathode-ray tube (CRT) teve to produce funky patterns back in the 80's.

You did it in a pitch dark room, aimed the camera towards the teve, and have someone briefly light a lighter in between. That generated a visual feedback loop.

By rotating the camera upside down, the feedback loop would introduce systematic effects, because the camera's vertical scan is now opposite to the teve's swipe. It would create random, constantly changing, colorful, spiraling patterns.

You could move your hands in front to adjust the patterns and control the brightness that could increase due to the feedback loop.

Stunning, cool, and fun.