What is the Hou Lian of the front curtain of the camera?

The shutter of a SLR camera works in four steps. Hou Lian is on, the front curtain is on (meaning the start of exposure), Hou Lian is off (meaning the end of exposure), and the front curtain is off. Front curtain synchronization means that the flash works when the front curtain is open. Hou Lian synchronization means that the flash flashes when the Hou Lian is turned off. But now strobe is used when the shutter speed is higher than1125, because the working principle of the shutter at this time is that the Hou Lian starts to close when the front curtain is not fully opened, and only a moving gap is left in front of the CCD (or CMOS) during exposure. If you only flash once, the light will be uneven, so use strobe. In layman's terms, this is probably the case. . . .