How to take photos written by flashlight with Canon SLR? have

Darkroom, is there a camera? Fix it on a tripod, first focus (in the position of your flashlight), and then switch to the manual focus position (MF). The camera can use these words 15 seconds. Press the shutter button after setting. Draw a word in front of the camera lens with a flashlight. If you draw in front, the word will be drawn at the back. It can be transferred by software. It's simple. As for cameras? How far is it? You can try it several times.