A few years ago, we shared a video on how the vertical scanning in digital cameras can distort fast-moving objects like fans and propellers. For example, the rotors in this digital photo of a drone are, in fact, perfectly straight:
A clever 15-year old on Imgur has created an elegant way of describing the phenomenon using mathematics. Here's his animation:
The black line represents the scanning line in the digital camera chip, and the blue curves represent the image captured thanks to the blades moving while the image was being scanned. In the online version of the animation, which was created using the mathematical calculator Desmos, you can even adjust the rotation speed of the propeller. A slower propeller results in slightly bent blades (as in the image above), while a very fast propeller generates multiple virtual blades.
Try it out yourself on a propeller aircraft or even a fast-moving ceiling fan. (If you get any good shots, share 'em in the comments below.) In the meantime, we're signing off for the weekend. See you back here on Monday!