Ceiling Fan Moves Faster When You Squint?

Lying here in bed, staring up at the ceiling fan and contemplating the universe, I notice that when I squint, the fan appears to move faster.

what’s up with that?

Huh, you’re right. My first hypothesis is that the vision blurs when you squint, and the increased blur gives the impression of increased speed. My second hypothesis is that with eyes wide open, your eyes make tiny movements to follow the movement of the blade, and this allows you to resolve the blades better. I’m not sure how to test either hypothesis though.

Another thing I noticed is that if you look away and see the fan in the corner of your eyes, it appears slower. This is easier to explain - peripheral vision is made up mostly by rods, and is more sensitive to movement than the central vision.

I think it’s a matter of contrast. When you squint, less light comes in, so your perception becomes more sensitive to small changes in the light level.
A quick search on “aperture and contrast” didn’t provide much to back me up on that though.

Boy does this take me back to my photography days :eek: . I think what you are seeing is the effect of circles of confusion. Rather than trying to explain it this page does a rather nice job of it. Keep in mind as you read the page that squinting your eyes would be similar to stopping down a camera lens. This having a direct effect on your eyes depth of field.

Interesting. The same thing seems to happen when I close one eye, although it doesn’t seem to speed up as much as with a squint.