Difference between revisions of "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.   
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{{Flickr_image
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|image_source= http://www.flickr.com/photos/camerawiki/5518947122/in/pool-camerawiki
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|image= http://farm6.static.flickr.com/5218/5518947122_96de763bb4.jpg
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|image_align= right
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|image_text= 1940 Goodspeed add-on flash synchronizer;<br>electrical contacts in shutter plunger
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|image_by= Voxphoto
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|image_rights= non-commercial
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}}
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[[Flash]] synchronisation, typically referred to as '''flash sync''', is the means by which electronic flash or [[flashbulbs]] can be fired at precisely the moment when the camera's shutter is fully open.   
  
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.
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==History==
  
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Before flash sync, cameras had to be set to '''bulb mode''' ('''B''') for flash photos. In dim light, the photographer would hold the shutter open, perhaps using a [[squeeze bulb]]. Then the flash would be manually fired (or in the earliest days, some form of flash powder ignited).  The photographer would then allow the shutter to close and the lights could be turned back on.
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In the 1940s, add-on flash synchronizers became common. To make a flashbulb shots using a press camera, the photographer would press a button on the flash handle. This would send current both to fire the flashbulb, and to energize a solenoid "tripper" connected to the shutter release. Other styles of synchronizers used the mechanical pressing of the shutter release to close an electrical contact.
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Eventually, the manufacturers of shutters began including internal sync contacts; and the ungainly add-on synchronizers vanished from the scene.
  
 
== Types of Flash Sync ==
 
== Types of Flash Sync ==
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The synchronisation mechanism of the shutter must take into account the delay between initiating the flash and the actual light output; a characteristic of the type of flash equipment. Flash bulbs, which produce their light by burning a small quantity of metal wire, have a delay that is significant relative to typical shutter times. Flash bulbs are coded with a letter representing their synchronisation delay. Many cameras have a switch allowing more than one delay to be selected. Some shutters use the same letter codes for  this. Others (for example the [[Zenit C]] and the [[Taylor-Hobson]] Talykron shutter) allow the actual delay to be set, in milliseconds.
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=== X 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. [http://www.photozone.de/3Technology/flashtec4.htm more info]
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'''X sync''' causes a Xenon tube or other type of electronic flash to fire in synchronization with the full opening of the [[shutter]], without any time delay between the two events. Cameras offering X Sync alone can only be used with older M Sync and F Sync flashbulb units at shutter speeds slow enough to allow the slower flash systems to reach their maximum light output before the shutter closes. When speaking about [[focal-plane shutter]]s, the X sync speed refers to the maximum speed that the camera can synchronize with the flash.<ref>More information on X-Sync [https://web.archive.org/web/20140109095319/http://www.photozone.de/standard-flash-sync here (archived)].</ref>
  
 
=== M Sync ===
 
=== 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.
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Some older cameras support '''M sync''', which supports flash sync with (now obsolete) medium-speed electric [[flashbulbs|flash bulbs]]. Class M flash bulbs have a firing delay of 18 to 22 milliseconds, so M-Sync is timed to fire the flash 20 milliseconds before the shutter reaches its peak opening, allowing the two events to coincide. <ref><i>[http://books.google.com/books?id=CU7-2ZLGFpYC&lpg=PP3&pg=PA459#v=onepage&q&f=false The Focal Encyclopedia of Photography</i>, Leslie Stroebel and Richard D. Zakia, Page 459]</ref>
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=== F Sync ===
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Cameras that support '''F Sync''' or Fast Sync are designed for fast-speed [[flashbulbs|flash bulbs]] that have a firing delay of approximately 5 milliseconds. A camera with F Sync will fire the flash 5 milliseconds before the shutter reaches its peak opening.
  
 
=== FP Sync ===
 
=== 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.
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Because cameras with [[focal plane]] shutters use two curtains, acting in sequence, to determine the overall exposure, there is a limit to the shutter speed you can use with flash that is close to instantaneous, including standard, traditional flash bulbs as well as basic electronic flash.  Any such flash source is only workable at or below a shutter speed which sees the whole film frame uncovered at the same time, i.e. when the first curtain has fully opened before the second curtain starts to close. With horizontal blind type shutters this generally limits the electronic flash sync speed to a maximum of 1/60 sec.
  
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. [http://www.photozone.de/3Technology/flashtec5.htm more info]
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This limit applies because, in order to achieve higher speeds from a focal plane shutter, the rear curtain begins to close soon after the front curtain has finished opening, forming a "travelling slit" that moves across the film plane. In this case, standard X-sync flash will not work, yielding only a partially exposed frame determined by the width and position of the slit at the time the flash fires.
  
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Focal plane high-speed sync, or '''FP-sync''', traditionally involved special, slow-burning flashbulbs that maintained nominally constant light output over the time it took the travelling slit to complete its journey across the film frame. With electronic flash such extended light output is not feasible, and advanced flash units have been evolved that provide a strobed output (rapidly repeated flash) as that "slit" moves across the film plane. This allows light from the flash head to expose the entire surface area of the film frame (or, these days, the digital imaging sensor) evenly, though at necessarily reduced flash output.<ref>More information on FP-sync [https://web.archive.org/web/20140109095340/http://www.photozone.de/hi-speed-flash-sync here (archived)].</ref>
  
 
== Types of Flash Sync Connections ==
 
== Types of Flash Sync Connections ==
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{{Flickr_image
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|image_source= http://www.flickr.com/photos/camerawiki/5517495802/in/pool-camerawiki
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|image= http://farm6.static.flickr.com/5139/5517495802_083e97b65b_m.jpg
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|image_align= right
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|image_text= PC sync socket
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|image_by= Voxphoto
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|image_rights= non-commercial
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}}
 
=== PC Terminal ===
 
=== 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.
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The standard '''PC''' terminal (from "[[Prontor]]&ndash;[[Compur]]") was by 1960 the nearly universal method for connecting a flash unit to a camera.  Electrically, a switch inside the camera closes a circuit between the two conductors of the PC connector, just as the shutter opens.  This triggers the flash to fire.
  
 
=== Hot Shoe ===
 
=== 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]].
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A '''[[hot shoe]]''' is an accessory holder (or accessory shoe) that has electrical flash sync contacts. The center contact and conductive metal sides work exactly as the PC connector does.
  
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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]].
  
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=== Older Types ===
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{{Flickr_image
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|image_source= http://www.flickr.com/photos/90900361@N08/15697253712/in/pool-camerawiki
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|image= http://farm4.staticflickr.com/3946/15697253712_98a6eb236a_t.jpg
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|image_align= right
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|image_text= ASA terminal on a 1952 Kodak
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|image_by= Geoff Harrisson
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|image_rights= wp
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}}
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Before the emergence of the PC connector as a global standard, several other flash sync terminals were in use: the ASA bayonet, dual pins, etc.
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{{br}}
 
== Shutter Curtain ==
 
== 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.
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Most [[focal plane shutter]]s 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 end the exposure.
  
 
=== Front Curtain Sync ===
 
=== 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.
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Generally, the flash sync fires at the instant the front curtain has fully opened.  This is called '''front curtain sync''', and it is used where it is desired that the flash freeze motion at the beginning of the exposure.  Front curtain sync is adequate for most flash-photography.  When making long exposures while also firing a flash, front curtain sync creates an effect where any motion blur - from ambient light - appears ''ahead of'' the subject, i.e. it appears to leave the subject behind. In the case of a moving motor vehicle in a night scene, for example, this can create an unrealistic effect since its headlamp and tail-lamp trails will extend out in front of it.
  
 
=== Rear Curtain Sync ===
 
=== 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.
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Some cameras offer the ability to fire the flash just before the ''second'' curtain ''closes''.  This is called ''rear'' (or ''second'') ''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 trailing the main subject.
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=== Focal Plane Shutter evolution ===
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Partially to address the low maximum shutter speeds usable with flash, later focal plane shutters, beginning with the [[Copal]] Square shutter from the 1960's, first commercially fielded on the [[Nikkorex F]], have lightweight metal or polymer blades, moving vertically. As these moved faster and over a shorter distance (the height of a 35mm frame as opposed to the width,) these allowed synchronization speeds of up to 1/250 sec.<ref>There is an illustration of a Nikon implementation of a Copal Square focal plane shutter [http://www.mir.com.my/rb/photography/hardwares/classics/nikkormat/elseries/el2/shutter.htm here].</ref>
  
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==Notes==
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<references />
  
 
== Links ==
 
== Links ==
 
* Vivid Light - [http://www.vividlight.com/articles/3311.htm Flash Photography Made Simple]
 
* Vivid Light - [http://www.vividlight.com/articles/3311.htm Flash Photography Made Simple]
 
* [http://www.kenrockwell.com/tech/syncspeed.htm Flash Sync Speed] KenRockwell.com
 
* [http://www.kenrockwell.com/tech/syncspeed.htm Flash Sync Speed] KenRockwell.com
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* A discussion of some old flash connections in [http://www.photomemorabilia.co.uk/Ilford/Flash_History.html a page about the Ilford flashguns]
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* [http://seandavisphotographic.com/blog/high-speed-flash-sync-freezing-action-with-flash/ high speed flash sync] by Sean Davis
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{{glossary}}
  
 
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[[Category:flash]]
{{glossary}}
 

Revision as of 01:33, 27 March 2019

Flash synchronisation, typically referred to as flash sync, is the means by which electronic flash or flashbulbs can be fired at precisely the moment when the camera's shutter is fully open.

History

Before flash sync, cameras had to be set to bulb mode (B) for flash photos. In dim light, the photographer would hold the shutter open, perhaps using a squeeze bulb. Then the flash would be manually fired (or in the earliest days, some form of flash powder ignited). The photographer would then allow the shutter to close and the lights could be turned back on.

In the 1940s, add-on flash synchronizers became common. To make a flashbulb shots using a press camera, the photographer would press a button on the flash handle. This would send current both to fire the flashbulb, and to energize a solenoid "tripper" connected to the shutter release. Other styles of synchronizers used the mechanical pressing of the shutter release to close an electrical contact.

Eventually, the manufacturers of shutters began including internal sync contacts; and the ungainly add-on synchronizers vanished from the scene.

Types of Flash Sync

The synchronisation mechanism of the shutter must take into account the delay between initiating the flash and the actual light output; a characteristic of the type of flash equipment. Flash bulbs, which produce their light by burning a small quantity of metal wire, have a delay that is significant relative to typical shutter times. Flash bulbs are coded with a letter representing their synchronisation delay. Many cameras have a switch allowing more than one delay to be selected. Some shutters use the same letter codes for this. Others (for example the Zenit C and the Taylor-Hobson Talykron shutter) allow the actual delay to be set, in milliseconds.

X Sync

X sync causes a Xenon tube or other type of electronic flash to fire in synchronization with the full opening of the shutter, without any time delay between the two events. Cameras offering X Sync alone can only be used with older M Sync and F Sync flashbulb units at shutter speeds slow enough to allow the slower flash systems to reach their maximum light output before the shutter closes. When speaking about focal-plane shutters, the X sync speed refers to the maximum speed that the camera can synchronize with the flash.[1]

M Sync

Some older cameras support M sync, which supports flash sync with (now obsolete) medium-speed electric flash bulbs. Class M flash bulbs have a firing delay of 18 to 22 milliseconds, so M-Sync is timed to fire the flash 20 milliseconds before the shutter reaches its peak opening, allowing the two events to coincide. [2]

F Sync

Cameras that support F Sync or Fast Sync are designed for fast-speed flash bulbs that have a firing delay of approximately 5 milliseconds. A camera with F Sync will fire the flash 5 milliseconds before the shutter reaches its peak opening.

FP Sync

Because cameras with focal plane shutters use two curtains, acting in sequence, to determine the overall exposure, there is a limit to the shutter speed you can use with flash that is close to instantaneous, including standard, traditional flash bulbs as well as basic electronic flash. Any such flash source is only workable at or below a shutter speed which sees the whole film frame uncovered at the same time, i.e. when the first curtain has fully opened before the second curtain starts to close. With horizontal blind type shutters this generally limits the electronic flash sync speed to a maximum of 1/60 sec.

This limit applies because, in order to achieve higher speeds from a focal plane shutter, the rear curtain begins to close soon after the front curtain has finished opening, forming a "travelling slit" that moves across the film plane. In this case, standard X-sync flash will not work, yielding only a partially exposed frame determined by the width and position of the slit at the time the flash fires.

Focal plane high-speed sync, or FP-sync, traditionally involved special, slow-burning flashbulbs that maintained nominally constant light output over the time it took the travelling slit to complete its journey across the film frame. With electronic flash such extended light output is not feasible, and advanced flash units have been evolved that provide a strobed output (rapidly repeated flash) as that "slit" moves across the film plane. This allows light from the flash head to expose the entire surface area of the film frame (or, these days, the digital imaging sensor) evenly, though at necessarily reduced flash output.[3]

Types of Flash Sync Connections

PC Terminal

The standard PC terminal (from "ProntorCompur") was by 1960 the nearly universal method for connecting a flash unit to a camera. Electrically, a switch inside the camera closes a circuit between the two conductors of the PC connector, just as the shutter opens. This triggers the flash to fire.

Hot Shoe

A hot shoe is an accessory holder (or accessory shoe) that has electrical flash sync contacts. The center contact and conductive metal sides work exactly as the PC connector does.

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.

Older Types

Before the emergence of the PC connector as a global standard, several other flash sync terminals were in use: the ASA bayonet, dual pins, etc.

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 end the exposure.

Front Curtain Sync

Generally, the flash sync fires at the instant the front curtain has fully opened. This is called front curtain sync, and it is used where it is desired that the flash freeze motion at the beginning of the exposure. Front curtain sync is adequate for most flash-photography. When making long exposures while also firing a flash, front curtain sync creates an effect where any motion blur - from ambient light - appears ahead of the subject, i.e. it appears to leave the subject behind. In the case of a moving motor vehicle in a night scene, for example, this can create an unrealistic effect since its headlamp and tail-lamp trails will extend out in front of it.

Rear Curtain Sync

Some cameras offer the ability to fire the flash just before the second curtain closes. This is called rear (or second) 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 trailing the main subject.

Focal Plane Shutter evolution

Partially to address the low maximum shutter speeds usable with flash, later focal plane shutters, beginning with the Copal Square shutter from the 1960's, first commercially fielded on the Nikkorex F, have lightweight metal or polymer blades, moving vertically. As these moved faster and over a shorter distance (the height of a 35mm frame as opposed to the width,) these allowed synchronization speeds of up to 1/250 sec.[4]

Notes

  1. More information on X-Sync here (archived).
  2. The Focal Encyclopedia of Photography, Leslie Stroebel and Richard D. Zakia, Page 459
  3. More information on FP-sync here (archived).
  4. There is an illustration of a Nikon implementation of a Copal Square focal plane shutter here.

Links

Glossary Terms