Flash synchronisation

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Flash synchronisation, typically referred to as flash sync, is a means by which a flash head is fired at precisely the moment when the camera's shutter is at its peak opening.

Before flash sync, cameras had to be set to bulb (B) mode in complete darkness. A cable release would be used to hold the shutter open, and the flash would be manually fired. The photographer would then allow the shutter to close and the lights could be turned back on.


Types of Flash Sync

X Sync

X sync causes the flash to burst in synchronization with the peak opening of the shutter. For some manual cameras, the X synch speed refers to the maximum speed that the camera can synchronize with the flash. more info

M Sync

Some older cameras support M sync, which supports flash sync with (now obsolete) medium-speed electric flash bulbs. Because flash bulbs take some time to generate light, M-sync is timed to open the shutter at the time when light output from the bulb is greatest.

FP Sync

Because cameras with focal plane shutters use two curtains, there is a limit to the shutter speed you can use with traditional flash. This is because the rear curtain begins to close soon after the front curtain has finished opening. At higher shutter speeds, both curtains move simultaneously, forming a "slit" that moves across the film plane. In this case, standard X-sync flash will not work.

Focal plane high-speed sync, or FP-sync, fires the flash repeatedly as that "slit" moves across the film plane, which allows light from the flash head to expose the entire surface area of the negative evenly. more info


Types of Flash Sync Connections

PC Terminal

A Prontor-Compur, or PC, terminal is the standard method for connecting a flash head to a camera. When the flash sync is triggered, a signal is sent from the camera along a wire to the flash telling it to fire.

Hot Shoe

A hot shoe is an accessory holder (or accessory shoe) that has an electrical flash sync contacts. A small, portable flash that has a contact on its "foot" can be connected to a hot shoe, which will cause the flash to fire when you press the shutter release.


Shutter Curtain

Most focal plane shutters are composed of two curtains: a front and a rear curtain. The front curtain slides open to begin the exposure, and then the rear curtain slides closed in the same direction to close the shutter.

Front Curtain Sync

Generally, the flash sync fires at the moment when the front curtain is at the beginning of its peak opening. This is called front curtain sync, and it is used to freeze motion at the beginning of the exposure. Front curtain sync is adequate for most flash-photography. When making long exposures while firing a flash, front curtain sync creates an effect where the motion blur appears to leave the subject behind.

Rear Curtain Sync

Some cameras offer the ability to fire the flash sync when the shutter is at the end of its peak opening. This is called rear curtain sync, and it is used to freeze motion at the end of the exposure. When making long exposures while firing a flash, rear curtain sync creates the effect of motion blur leading up to the subject.


Links

Glossary Terms