The wider the better. For example, the common lens group of SLR is the lens that comes with it when buying SLR. Generally from 18mm, you can shoot long legs. If possible, it will take longer to buy 16mm or even 14 mm. In addition, it is also important to carefully arrange the picture. Putting your feet on the edge of the picture will give people the feeling that you want to extend the picture indefinitely. There is also the lens angle, and the foot is in front of the photographer, which will also bring the influence of the change of perspective. Use these aspects together, and you will make your sister love you to death.