One of the most important concepts in flash photography is sync speed. This is the fastest shutter speed that your camera can use with normal flash. For most DSLRs, the sync speed is 1/250″. Your camera’s sync speed may be faster or slower — so check your user manual if you don’t know.

Why can’t I use flash at any shutter speed I want? This is a fair question. It has to do with the design of your camera’s shutter. If you use a DSLR or an old-school 35mm film camera, your shutter mechanism has two curtains in front of the sensor/film plane. During the exposure, the 1st/front curtain opens and then the 2nd/rear curtain closes. The difference in timing between the movement of the two curtains is your shutter speed.

At many shutter speeds, the 1st-curtain will completely clear the sensor before the 2nd-curtain begins to close. If your flash fires at any of these speeds, the entire sensor will see the flash — which is what you normally need to make a flash photo. Your sync speed is the fastest shutter speed at which the 1st-curtain completely clears the sensor before the 2nd-curtain begins to move.

At faster shutter speeds, the 2nd-curtain begins to close before the 1st-curtain is completely open. The shutter literally becomes a slit between the curtains that moves across the sensor. So, there is no point at which the flash can illuminate the entire sensor.

High-Speed Sync is a special flash mode that changes the way your Speedlite fires. Rather than fire one big pulse of light, HSS turns the Speedlite into a machine-gun of light that fires an insanely-fast series of pulses. Essentially the Speedlite becomes a continuous light source for a very brief period of time. The downside is that HSS consumes a ton of power. So, your Speedlite in HSS is 2.5 stops dimmer than it is in normal mode. There are loads of reasons to use HSS. Click here for the many articles I’ve written on HSS.

More Tid-Bits About Flash and Sync

Photo shot with shutter faster than camera sync speed

The black band in this shot is evidence that the shutter speed was faster than the camera's sync speed. If the camera does not sense that a flash is attached, then it will not limit the shutter to the sync speed.

Your Camera Might Not Know That You Are Using Flash

If your camera senses that a Speedlite is attached and turned on, then it will impose the limitation of sync speed. However, there are several situations when the camera will not know that you are using a flash. In these cases, the camera will fire at any shutter speed you specify. As shown above, when the shutter speed exceeds the sync speed, you’ll get a black band on a portion of your photograph. So, you need to be mindful of the sync speed in the following situations:

  • using a Nikon Speedlight with a Canon camera or vice-versa
  • using a radio trigger to activate your off-camera flash
  • using a PC-sync cord
  • using an infra-red trigger to fire flashes via optical slave sensors
Why Outdoor Flash “Overexposes” Your Photos

Using your flash outdoors in bright sunlight is a smart idea because your camera cannot record the full ranges of brights and darks that you can see. Outdoors, in bright sunlight, the shadows will often be too dark. Turning your flash on in bright sunlight will throw “fill flash” into the shadows so that the camera can record those important details.

If you’re using a wide-aperture to create shallow depth-of-field that hides distracting background details, then under bright sun, you’re also using a fast shutter speed. So, when you turn your Speedlite on for fill flash, the camera slows the shutter back down to the sync speed — even if the camera is in shutter-priority (Tv) or manual mode. So, if you just turned your Speedlite on and your photo looks way over-exposed, you need to activate high-speed sync so that the camera can return to using fast shutter speeds.

Some Cameras Have Very Fast Sync Speeds

For most of us, the sync speed is imposed by the mechanics of the common two-curtain shutter used in SLRs. If your camera does not have a two-curtain shutter, then you likely have a much faster sync speed or no sync speed at all. For instance, the shutter in a view camera lens is made of blades that open from the center out to the edges (much like the design of the aperture mechanism). So with view cameras and some medium-format cameras, sync speeds can be very fast. Another example is the digital cameras that have electronic shutters. With these, the sensor literally turns on and off very quickly. So the sync speed can be 1/500″ or faster.

X-Sync Is The Same As Sync Speed

Old-schoolers will refer to sync-speed as the X-Sync because cameras used to have an X on their shutter dials to indicate the maximum speed with flash. So, when you read “X-Sync” just think “Sync Speed.”

For more details on sync speed and flash photography in general, check out my Speedliter’s Handbook.

18 Responses to Sync About It…or Thinking About Syncing

  1. Michael says:

    Nice article, something to point my fellow club members to when they ask questions.

    One nit, X-Sync. I was told way back in the dark ages before digital this stood for "Xenon electronic flash" and M-Sync was for Medium speed flash bulbs (20 ms delay in peak output). Class M bulbs were the most common.

  2. Victor says:

    Is it possible to have good sync speed below 1/200? I find myself dropping to 1/30 at times and I still get good light. Is it my triggers?

    • Syl Arena says:

      Hey Vic – Sync speed refers to the fastest shutter speed that you can use normally. Any shutter speed slower than your camera’s sync speed will also sync with your flash. The reason to use longer (aka: slower) shutter speeds is to collect more ambient light from the background — typically the dimmer the ambient, the longer the shutter speed.

      • Victor says:

        Yes makes perfect sense and thats exactly what I'm looking for. Genius! Thank you so much. Broke it down perfect. Again luv your book. Its my bible at the moment. Have done some great work for a rookie following your book "Speedliter's Handbook" Again very grateful for the reply.. You rock!

  3. Kevin Miller says:

    This is the clearest explanation of high speed sync that I have come across. The illustrations are a very helpful part of this. Thanks for sharing.

  4. Dembo says:


    I think your diagram for "Normal Sync" is quite misleading: It gives the impression that flash duration equals X-Sync time while in fact the flash duration usually is much shorter.

    I suggest referring to page 53 of the excellent Speedlighter's Handbook written by a guy called Syl Arena, it gives the correct relation between X-Sync time and flash duration. 😉

    • Syl Arena says:

      Hi Dembo – Thanks for the shout-out on the Handbook. For those who do not have the book at hand, the figure on page 53 is a composite of two oscilloscope captures of a 580EX II firing at 1/2 and 1/128 power. The Normal Sync diagram above shows the exposure from a different perspective. The three center frames in the diagram represent the entire duration of the exposure — not just the center frame. So, as I see it, the diagram is correct in that it shows that the flash duration is still a fraction of of the exposure time and that the flash must fire between the movement of the two curtains. To avoid the confusion in the future, I’ll heed your advice and tighten the flash graph up a bit. Thx. for the comment! It’s always great to hear how others perceive my work.

  5. David ziser posted a great video of how to cheat sync with flash espically if tou are a wedding photographer have a look when you get a chance as it was something i never thought of but so simple and Syl great post as usual i should write to you more 🙂

  6. […] Wenn die Belichtungszeit kürzer wird, dann ist irgendwann der Punkt erreicht, an dem der zweite Vorhang schon zugeht, bevor der erste Vorhang den Sensor komplett freigelegt hat. Somit hat das Blitzlicht keine Chance, Licht auf den gesamten Sensor zu bringen und der vom Verschluss verdeckte Teil des Sensors bleibt dann dunkel. In diesem Artikel ist das sehr schön mit Diagrammen erklärt: Sync About It […]

  7. Greg says:

    I’m assuming your ‘example’ (skateborder) is manufactured, rather than a genuine example? The reason I ask is because it appears to be a mix of ambient (blue sky, sun top left) and flash (fill). Surely sync failure would only affect the fill-flash element, and the ambient, i.e. the blue sky, would be unaffected throughout the frame? If I saw this I would assume the shutter had failed!

    • Syl Arena says:

      Greg – This is a straight shot out of my 5DM2 using three Speedlites in high-speed sync (one as master, the other two as slaves). Not sure what you mean by “sync failure.” In normal sync, the camera will force the shutter back to the sync speed (1/200″ for the 5DM2) which typically overexposes the image. If a non-Canon flash is in the hotshoe, then a black band will appear across the bottom of the frame — the faster the shutter speed, the wider the band.

      • Greg says:

        What I don’t understand from the example is; if the background blue sky is the ambient exposure and determined by shutter speed/aperture (i.e. not influenced by flash power or sync with the shutter), why is it not uniform across the frame? Surely only the fill light would be cut off? Why would both the ambient exposure and flash exposure elements be affected by the failure of the flash to sync with the shutter? I have your book and is very good, but I never fully understood this example.

  8. […] de externe strobe bediend? Of anders, kijk hier even, ik denk dat dit toch je probleem verklaard: KLIK Mvg, Rudy Mas Nikon D5100 Met citaat reageren « De nieuwe Olympus […]

  9. Matt says:

    Hi Sly, I tried sending you an email, but it got bounced back to me. Can I confirm your address ?

  10. […] times Maybe this will help you to understand…. Sync About It?or Thinking About Syncing | PixSylated | Syl Arena's Photography Blog on Light & I… Normal flash.. 1 big flash… when the shutter is fully open (synced) High Speed Sync flash.. lot […]

  11. […] that’s too fast, wouldn’t work with synched flash – to read more on it, click here). The flash, which was triggered by the remote piece attached to the top of the camera, would fire […]

  12. michael says:

    when using speed sync, the flash must fire a little delay to get a proper timing with the shutter window. when the flash not support hss, it will always fire with the timing of shutter button not with the timing of shutter window so that your image get blank band because the flash end first before the shutter window finish cycle. im sorry with my English but that is the truth.

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