Photographer asks for help: What is the principle of high-speed synchronization of external flash? Generally, cameras have X-sync speed. If my d7000 camera

Speaking of high-speed synchronization, it is necessary to explain the working process of SLR shutter first. Generally, when the shutter speed is lower than 1/200 (or 1/250 for medium and high-end machines), the Hou Lian will be closed after the shutter front curtain is fully opened. However, when the shutter speed is higher than this value, before the front curtain is completely opened, the Hou Lian has started to move, and the gap formed by the front curtain and the back curtain sweeps across the CMOS surface, ensuring that the exposure time of each area of CMOS is the preset exposure time, but the whole shutter action time is still 1/200 (or 1/250).

The continuous flashing time of any flash cannot be as long as 1/200 seconds, so when the shutter speed is high, the picture will be underexposed (even completely black) at the lower part, and the underexposed area will extend upward with the increase of shutter speed. The high-speed synchronous flashing lamp solves the above problems by continuously emitting multiflash within 1/200 seconds. X value can be understood as the highest shutter speed at which the machine shutter can be fully opened. When the shutter speed is less than or equal to this speed, any flash can be used for normal exposure.

Due to the core technology, the exposure of domestic TTL flash is not very accurate, especially when using high-speed synchronous flash and strobe. Yongnuo quality is not bad, as long as it is not a constant time and high power continuous flash. The flash supporting Nikon TTL means supporting CLS (in fact, this can be understood as the instruction system name of Nikon TTL), but it does not mean supporting high-speed synchronization; Installed on the top of the machine, it can be used directly, and the built-in flash of D7000 can be used outside the machine (just set it to command mode), so there is no need to buy an external flash (if the overhead light is used to flash, it needs to support the main control function, so that the external light can be controlled to flash correctly according to the camera settings).