system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are camera lenses round but photographs are square/rectangular?
gpt
Because it is easier to cut a round magnifier than a rectangular one, also, most cameras are not fixed lens, which means they have interchangeable lenses, it is easier to connect something using a thread than clasps, round objects take to threads easier than rectangular object.  It has nothing to do with the final shape of the image why lenses are round.  The reason why the image is rectangular is because the sensor and film cells is rectangular, if the focal pattern created by the lens is smaller than the sensor or film cell you get a grayish black circular outline, anything larger will expose the entire area thus no circular outline.