Problems of SLR photography How to show three problems of selfie photography in photos?

Just use the camera's door B. I've seen this before. At that time, we took two pictures and exposed them twice. You must expose this photo five or four times. Adjust the shutter speed to door B first, and then adjust the aperture. When shooting, keep the whole photo space dark, keep the flash on and turn off the lighting. People pose, press the shutter once, keep the dark environment, pose the next position, pose and shoot again, and the third position is the same, pose and shoot again, while light painting only keeps the brightness of the luminous body while moving slowly, and the shutter is open when the camera moves. It's okay, this is my reasoning, because I don't have that much troubleshooting, just two exposures. Two figures, I wanted to send a photo, but I couldn't find it at the moment.