> You really need to know the sensor size to adjust accordingly. Absolutely. Focus length without sensor size (or film size) is a meaningless indicator for FOV

> You really need to know the sensor size to adjust accordingly. Absolutely. Focus length without sensor size (or film size) is a meaningless indicator for FOV. But when it comes to a FOV being equivalent to the human eye, surely we should take display size into account as well. A photo made with a 500mm lens displayed at 4"x6" has exactly the same perspective as a photo taken from the same place with a 50m lens, displayed at 40"x60". In fact that small picture is basically the same as the large one cropped to the size of the small one. It's a factor I never see mentioned. The usual explanation is that a "normal" lens gives more or less the same image when we look through the viewfinder as when we look directly, without the camera. But we don't look at photographs through a camera's viewfinder; we see them on our screens, on billboards, on prints.