Huh, that’s weird, because I have in fact experienced what I described many times while looking at fans (physically, not through video)! The blades would seem to be spinning slowly, and sometimes reverse direction. I hadn’t ever even heard of aliasing, it was just mysterious to me.
Was it indoors or outdoors? Like I said, electric lights often have a flicker frequency (50 or 60 Hz depending on country, or some multiple of that).
The same thing can happen with musical instruments btw. When I play guitar indoors, sometimes I can see the string “wobble”, much slower than the sound frequency ought to be. I’m pretty sure that’s because of the interplay between string frequency and light flicker. In sunlight it doesn’t happen.
It was almost always indoors, so that might have been it. I just did an experiment: I turned on a fan I have in my room, while no electric lights were on (only sunlight through the window). Looking at the blades, they indeed seemed like a blur that didn’t resolve into individual blades. However, when I changed the speed of the fan, it seemed like a part of the blur resolved into a bunch of blades that slowed down their spin and changed directions. The blades didn’t fully resolve into visibility, and there were more blurry kind of visible blades than there should have been blades in the fan, but it was very clearly happening (multiple times as I changed the speed back and forth, though not every time I changed the speed). Weird.
Huh, that’s weird, because I have in fact experienced what I described many times while looking at fans (physically, not through video)! The blades would seem to be spinning slowly, and sometimes reverse direction. I hadn’t ever even heard of aliasing, it was just mysterious to me.
Was it indoors or outdoors? Like I said, electric lights often have a flicker frequency (50 or 60 Hz depending on country, or some multiple of that).
The same thing can happen with musical instruments btw. When I play guitar indoors, sometimes I can see the string “wobble”, much slower than the sound frequency ought to be. I’m pretty sure that’s because of the interplay between string frequency and light flicker. In sunlight it doesn’t happen.
It was almost always indoors, so that might have been it. I just did an experiment: I turned on a fan I have in my room, while no electric lights were on (only sunlight through the window). Looking at the blades, they indeed seemed like a blur that didn’t resolve into individual blades. However, when I changed the speed of the fan, it seemed like a part of the blur resolved into a bunch of blades that slowed down their spin and changed directions. The blades didn’t fully resolve into visibility, and there were more blurry kind of visible blades than there should have been blades in the fan, but it was very clearly happening (multiple times as I changed the speed back and forth, though not every time I changed the speed). Weird.
Yeah, I can’t check right now, but my guess is some electrical effect when changing fan speed.