I noticed this tonight when pointing my phone camera at my PC. I’m not sure if it has to do with the camera switching lenses or what because I am using an iPhone XS Max so maybe it has something to do with going between the standard lens and the telephoto lens? Would love some info on this, I have attached a link to a video of what i’m talking about.
[Fan switching direction?](https://imgur.com/gallery/ZaJJDzt)
Your camera is taking pictures at a slower rate than your fans are spinning giving the illusion that they are “moving” slowly enough to see the direction. Because this rate isn’t perfectly timed, the pictures eventually capture the fake motion at a point where the blade is further in the opposite direction giving the illusion that the movement has reversed.
Edit: Realising I didn’t really answer your question… Your phone zoom isn’t really mechanical meaning the more you zoom the more your camera has to process the video. This likely results in the actual frame rate of your video changing which fits within the answer above.