Photography / Tips and Solutions

Sync Speed versus Flash Duration


Sync Speed versus Flash Duration: Flash duration is a measurement of the burst of light that creates the exposure. While flash durations are almost always shorter than the shutter speed, there are times―especially when working on larger sets at full power―when the camera’s shutter speed can be shorter than the flash duration. These times should be avoided. When shooting with flash, the synchronizing issues between your camera and your studio lights must be addressed.

Every camera has a maximum flash sync speed, which is the fastest shutter speed you can use when shooting with flash.* It’s important to note that the top sync speed indicated on the specs is often the top sync speed for shoe-mounted Speedlites, which is often faster than the top sync speed for studio lights. As an example, one manufacturer lists a top sync speed of 1/300th-second for Speedlites, but only 1/250th-second for studio flash.

With few exceptions, the top sync speed on most compact DSLRs is 1/125th-second to 1/200th-second, and 1/250th –second for pro DSLRs containing focal plane shutters. DSLRs containing leaf shutters have top sync speeds of up to 1/800th –second or faster.

Shutter Clipping No Shutter Clipping

As an example, if your camera is set to 1/250th-second and the flash duration is longer than 1/250th-second, you’re going to experience “clipping,” which means the tail end of the flash exposure is not going to be recorded, which in turn can result in an uneven exposure and/or a color shift in the final image. (During the course of the flash exposure, the color temperature of the flash, like a candle flame, goes from warm (yellow) to cool (blue). What this means is if you should clip the flash exposure, the tail end of the exposure might suddenly shift to yellow.

It’s important to note that few flash meters have the ability to record the speed of the burst rate, which means it’s always a good idea to set the shutter speed of your camera one to two speeds slower than the highest sync speed, to ensure that you are recording the entire duration of the flash exposure.

*You can use faster speeds, but there will be a cut-off shadow going across the left or right side of the image that covers larger portions of the frame each time you increase the shutter speed.

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Why is flash duration important to freeze action when its so much faster than shutter speed.Say you have a flash duration of 1/5000 and a sync speed of 1/250. Are you not just freezing it at the  sync speed?

If you are shooting in a dark setting, for all intents and purposes, the flash duration will become your shutter speed: the light will be hitting the sensor for only the amount of time it is available (the flash’s duration).  So, it wouldn’t matter if your max sync speed is 1/250th of a second, you could shoot with a longer shutter speed and the sensor would still only be exposed to the light for the duration of the flash.  Again, this would be in a dark setting such as a studio (where you can control the ambient light) or a stage/auditorium. 

Useful information. Perhaps you can help me solve my problem of shooting with a flash in shutter priority mode. When I set a shutter speed in shutter priority mode in my 50D and shoot with a speedlight, the camera overides my set speed and sets it own, usually slower one. This contradicts what the camera and flash hand books say (that the shutter speed should not change). Is there something I am doing wrong or missing?