The SLR does not need a flash, and it is half bright and half unlit.

This is because the shutter speed is higher than the flash synchronization speed. When the shutter speed is set to 1/200 seconds, black will not appear.

"Synchronization" in flash photography means that the flash flashes just when the shutter is fully opened.

Because the flash duration of electronic flash is extremely short, if the flash is not triggered when the shutter is fully open, the whole picture will feel insufficient flash, or some pictures will flash, some pictures will not flash, or even the whole picture will not feel flash. These situations are called "out of sync". It is not difficult to understand that when you take flash photography, ensuring "synchronization" is the premise. For cameras and flashlights with normal performance, the synchronization effect is directly related to the shutter speed used.

Flash synchronization speed of different cameras is different. Traditional film cameras are mostly between 1/60s and1.250s (of course, there are higher or lower flash synchronization speeds. The synchronization speed of the flash will be marked with different colors on the scale corresponding to the camera's quick dial. As long as the flash synchronization speed or any other shutter speed slower than the flash asynchronous speed is applied, the flash can be synchronized.