Flash photography I don't know why there are shadows.

This is a typical manifestation of unsynchronized exposure in flash photography. The higher the shutter, the bigger the black edge.

The solution is to reduce the shutter speed. Generally, the maximum is not more than 1/250 seconds, and some cannot exceed 1/200 seconds, or even lower.

The general solution is to set it to1125 seconds, which is suitable for any camera and flash.