What does synchronization mean in photography?

This synchronization refers to flash synchronization.

Explain a few related concepts first.

Camera shutters can be roughly divided into two categories, one is mirror shutter and the other is curtain shutter.

The latter is the most common in modern SLR cameras.

In the early years, it was a curtain shutter that moved left and right.

At present, almost all 135 digital SLR shutters are vertical (moving up and down) rigid shutters.

Take this as an example:

Shutters are generally divided into two groups: front curtain and Hou Lian. Usually, two sets of shutter blades cover the photoreceptor.

At the moment when the shutter is pressed, the front curtain begins to move, gradually exposing the photoreceptors (CCD, CMOS, film).

Until the photoreceptor is completely exposed.

At this time, if your exposure time reaches, say, one thirtieth of a second, the shutter Hou Lian starts to move and gradually covers the photoreceptor to complete the exposure.

Although the moving speed of the shutter blade is extremely high, it will take some time for the longitudinal shutter blade to travel this long distance of 24mm (although it is short and fast). For the high-speed shutter of the camera, that is, the limit exposure time, such as11000 seconds, 1/4000 seconds, etc. After the shutter front curtain starts to move, it hasn't waited until the whole photoreceptor is exposed.

That is to say, in such a short time as11000 seconds, the photoreceptor has never been completely exposed, and the exposure is completed through a gap sandwiched between the front curtain and the Hou Lian.

The shorter the exposure time (the higher the shutter speed), in fact, the physical speed at which the shutter blade moves is constant. The "shutter speed" here is an unscientific statement in photography for decades. The narrower the gap formed by the front and rear curtains; The longer the exposure time,

The wider the slit formed by the front and rear curtains is, the complete photoreceptor is exposed when the maximum width is 24 mm.

In addition to the flash, the flash is very bright, but its luminous duration is extremely short, usually about one tenth of a second.

If the shutter is pressed, the shutter blade flashes in the fully open state and the photoreceptor is completely exposed, then the whole photoreceptor, that is, the whole picture, can receive light.

However, if the exposure time is very short, that is, a "high-speed shutter", a slit is formed between the front curtain of the shutter and the Hou Lian to sweep the photoreceptor at the moment of flash illumination, so the whole picture cannot be illuminated, and only that slit can be illuminated.

That is to say, in normal use of the flash, it is necessary to ensure that the front and rear curtains of the shutter blade do not block the photoreceptor for at least a moment, and the flash flashes only when the CCD or film is fully exposed, so as to ensure the integrity of the picture. Otherwise, some of them will be covered up.

It can be ensured that the front and rear curtains of the shutter blade do not block the photoreceptor, and the exposure time ("shutter speed") when the photoreceptor is fully exposed is the flash synchronization time ("flash synchronization speed") of this camera.

The synchronization time of early horizontal curtain shutter cameras was only about 1/45 seconds (long horizontal distance, 36mm).

Now the shutters move vertically, and the synchronization time is shortened from 1/60 and1125 to 1/250 seconds.

Due to the different technologies of different manufacturers and different camera grades, the synchronization time of each model of flash is different.

I don't know if I made myself clear. If you have any questions, please ask.