YouTuber builds a camera that films light at 2 billion fps

Okay I just had to share this astonishing video. Dr Brian Haidet, who runs the AphaPhoenix YouTube channel, built this camera to observe light bouncing off mirrors. The video shows how he made it (and there’s a more technical video with fuller details on that) but also shows that positioning the camera to one end makes the light look like it’s accelerating as it moves towards the camera. Extra marks for anyone who can work out why without viewing the answer in the video…