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X-sync is the simplest to explain and implement: the flash is fired at the instant the shutter is fully open. Electronic flash equipment produces a very short flash.
Cameras designed for use with flash bulbs generally had one or more of S (slow) sync, M (medium) sync, F (fast) sync, or FP/FPX (flat peak) sync, designed for use with corresponding bulb types. These sync modes close the contacts a few milliseconds before the shutter is open, to give the flashbulb time to reach peak brightness before exposing the film. Class M bulbs reach their peak illumination 20 milliseconds after ignition, and class F lamps reach their peak at approximately 5 milliseconds.
FP sync was used with FP (flat-peak) flash bulbs designed specifically for use with focal-plane shutters. In these shutters, although each part of the film is exposed for the rated exposure time, the film is exposed by a slit which moves across the film in a time (the "X-sync speed") of the order of 1/100"; although the exposure of each part of the film may be 1/2000", the last part of the film is exposed later by the X-sync time than the first part, and a brief flash will illuminate only a strip of film. FP bulbs burned close to full brightness for the full X-sync time, exposing the whole frame even at high shutter speeds.
The Nikon F offered FP, M, and ME bulb synchronizations, in addition to the X sync.
X (xenon) sync is a mode designed for use with electronic flash. In this mode, the timing of the contacts coincides exactly with the full opening of the shutter, since
In photography
Photography is the visual art, art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It i ...
, flash synchronization or flash sync is the synchronizing the firing of a photographic flash with the opening of the shutter admitting light to photographic film or electronic image sensor.
In camera
A camera is an optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), with a ...
s with mechanical (clockwork
Clockwork refers to the inner workings of either mechanical devices called clocks and watches (where it is also called the movement) or other mechanisms that work similarly, using a series of gears driven by a spring or weight.
A clockwork mec ...
) shutters synchronization is supported by an electrical contact
An electrical contact is an electrical circuit component found in electrical switches, relays, connectors and circuit breakers. Each contact is a piece of electrically conductive material, typically metal. When a pair of contacts touch, they ...
within the shutter mechanism, which closes the circuit at the appropriate moment in the shutter opening process. In electronic digital camera
A digital camera is a camera that captures photographs in digital memory. Most cameras produced today are digital, largely replacing those that capture images on photographic film. Digital cameras are now widely incorporated into mobile devic ...
s, the mechanism is usually a programmable electronic timing circuit, which may, in some cameras, take input from a mechanical shutter contact. The flash is connected electrically to the camera either by a cable with a standardised coaxial PC (for Prontor/Compur) 3.5 mm (1/8") connector (as defined in ISO 519), or via contacts in an ''accessory mount'' ( hot shoe) bracket.
Faster shutter speeds are often better when there is significant ambient illumination, and flash is used to flash fill subjects that are backlit without motion blur
Motion blur is the apparent streaking of moving objects in a photograph or a sequence of frames, such as a film or animation. It results when the image being recorded changes during the recording of a single exposure, due to rapid movement or ...
, or to increase depth of field
The depth of field (DOF) is the distance between the nearest and the furthest objects that are in acceptably sharp focus in an image captured with a camera.
Factors affecting depth of field
For cameras that can only focus on one object di ...
by using a small aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane.
An ...
. In another creative use, the photographer of a moving subject may deliberately combine a slow shutter speed with flash exposure in order to record motion blur of the ambient-lit regions of the image superimposed on the flash-lit regions.
S, M, F, FP, X and HSS sync
X-sync is the simplest to explain and implement: the flash is fired at the instant the shutter is fully open. Electronic flash equipment produces a very short flash.
Cameras designed for use with flash bulbs generally had one or more of S (slow) sync, M (medium) sync, F (fast) sync, or FP/FPX (flat peak) sync, designed for use with corresponding bulb types. These sync modes close the contacts a few milliseconds before the shutter is open, to give the flashbulb time to reach peak brightness before exposing the film. Class M bulbs reach their peak illumination 20 milliseconds after ignition, and class F lamps reach their peak at approximately 5 milliseconds.
FP sync was used with FP (flat-peak) flash bulbs designed specifically for use with focal-plane shutters. In these shutters, although each part of the film is exposed for the rated exposure time, the film is exposed by a slit which moves across the film in a time (the "X-sync speed") of the order of 1/100"; although the exposure of each part of the film may be 1/2000", the last part of the film is exposed later by the X-sync time than the first part, and a brief flash will illuminate only a strip of film. FP bulbs burned close to full brightness for the full X-sync time, exposing the whole frame even at high shutter speeds.
The Nikon F offered FP, M, and ME bulb synchronizations, in addition to the X sync.
X (xenon) sync is a mode designed for use with electronic flash. In this mode, the timing of the contacts coincides exactly with the full opening of the shutter, since xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
flashes respond almost instantly.
Due to their construction, focal plane shutters, as used on most SLRs, only allow normal xenon flash units to be used at shutter speeds slow enough that the entire shutter is open at once, typically at shutter speeds of 1/60 or slower, although some modern cameras may have an X-sync speed as high as 1/500 (e.g. Nikon's D40 DSLRs). Special electronic flash units for focal-plane shutters fire several times as the slit moves across the film. Electronic shutters used in some digital cameras do not have this limitation and may allow a very high X-sync speed.
Leaf shutters, which are generally situated within the lens housing, open to expose the entire image at once, and therefore allow flash sync across all shutter speeds (up to 1/1600" with a Schneider Kreuznach lens on a Phase One/Mamiya 645DF camera).
The Synchro-Compur leaf shutter of the Braun Paxette Reflex Carl Braun Camera-Werk of Nuremberg, Germany, or Braun, as it was more commonly called, was founded as an optical production house. It is best known for its 35mm film cameras named Paxette, and for slide projectors named Paximat.
History
The com ...
offered V, X, and M flash synchronization, whereby V (German: "Vorlauf") was used in conjunction with self-timer.
Higher sync speeds are useful as they allow ambient light to be controlled by increasing shutter speed rather than reducing aperture. This enables the same ambient light exposure at a larger aperture; this larger aperture in turn reduces the amount of flash output necessary to illuminate a subject.
Today, certain modern xenon flash units have the ability to produce a longer-duration flash to permit flash synchronization at shorter shutter speeds, therefore called high-speed sync (HSS). Instead of delivering one burst of light, the units deliver several smaller bursts over a time interval as short as 1/125 of a second. This allows light to be delivered to the entire area of the film or image sensor even though the shutter is never fully open at any moment, similar to FP sync.
Rear-curtain sync
Many digital SLRs include an option to fire the flash just before the closing of the shutter, so that moving objects will show a streak where they came from and a sharp image where they were at the end of the exposure—useful for moving objects to convey a sense of speed. This mode is called ''rear-curtain sync'' or ''2nd-curtain sync''.See also
*Guide number
When setting photoflash exposures, the guide number (GN) of photoflash devices (flashbulbs and electronic devices known as "studio strobes", "on-camera flashes", "electronic flashes", "flashes", and "speedlights")The Nikon brand name for its came ...
* Through-the-lens metering (TTL)
References
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