Before we get to the high speed let us have a look at flash triggering.

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1 In search of high speed flash synchronisation Before we get to the high speed let us have a look at flash triggering. All cameras have a maximum synchronisation speed, typically between 1/125 and 1/250 of a second, so what does this mean? When the shutter is pressed the first curtain travels across the sensor. Once the sensor is uncovered the flash is set off and exposes the image. The second curtain closes and the shutters are reset. The camera knows how much time to allow between triggering the first curtain and when the whole sensor can be exposed to light, often called pre-flash. If a shutter speed higher than the sync speed is chosen part of the image will not be exposed, in this case the 2 nd shutter was moving to stop exposure when the flash illuminated Leaf shutters

2 Many medium format cameras had leaf shutters which allowed flash sync at any speed. The wedding photographers of old took advantage of this to use fill in flash even in bright sunlight, after all the Hassleblad 500C had a top shutter speed of 1/500s against SLRs of the time that had 1/60s or 1/90s sync. Modern requirements Modern photographers talk of terms like Bokeh and like large apertures so that the background is thrown out of focus. Using the sunny 16 rule the shutter speed is the same as the ISO in sunny conditions and the aperture is f16 so if we want to use f2.8 then we need a shutter speed of 1/4000s (fill flash is normally 1½-2 stops lower) and fill at about f1.4-f1.8. The solution Actually there are a number of solutions and as far back as 1992 Nikon produced a flashgun with what they called Auto-FP sync and Canon came along with High Speed Sync (HSS). In essence these are not single flashes of light but a stream of lower powered flashes (approx 20% of full power) at such a high rate (10s of thousands of pulses per second) that it looks like continuous light, well at least to the sensor it does. In the Nikon system in such cameras as the D800, D700 etc. the sync speed can be set where FP flash cuts in, if 1/250 (Auto FP) is selected it means that FP flash will be used at shutter speeds of 1/320 and higher and if 1/320 (Auto FP) is selected then FP flash is used at 1/400 and higher. FP or HSS mode needs to be built in to the flash to be used and any triggering systems need to have the signalling system built in to activate it. Of course many flashes such as most studio flash do not support these high speed sync systems. One effect of High Speed Sync is that the effective power of the flash is reduced by about 2 stops (1/4 power) PocketWizard About 2009 along came PocketWizard with the TT1/TT5 system and 2 different timing adjustments.

3 The first is Peak Sync where a small gain can mean that 1 or 2 shutter speeds higher than x- sync speed can be used i.e. instead of 1/250 maybe 1/500 would be achievable, it allows you to squeeze a bit more out of a standard flashgun. This is achieved by firing the flash just a bit earlier so that the peak has completed before the 2 nd curtain moves. The second method is using the long tail of the flash pulse which is what PocketWizard call Hypersync which although not a new technique it was not commonly used. Those that knew of it would have called it Long Tail Sync. This relies on flash having a long (slow) pulse, not the sort you get from hot shoe flashguns (IGBT) but rather studio flashes or the larger portable flash systems. Some Insulated Gate Bipolar Transistor (IGBT) flashes can be used for Hypersync because the flash pulse is long enough, however this can normally only be done at full power as their method of power control is to switch off in the middle of the pulse and not release the full power. Capacitor based lights such as studio lights are very different and their output is controlled by how high they are allowed to charge to and a strange effect is that if they are charged to a lower power it actually takes them longer to discharge. This means that most studio lights can be used at all power for Hypersyncs. Because Hypersync is using the low power in the tail it will also be about 2 stops below what we would get if at X-sync. A second point to note is that the power level is higher at the start of exposure compared to the end which produces the characteristic Hypersync image which is brighter at the bottom of the frame compared to the top. Hypersync Triggers Recently a number of triggers have appeared featuring their own version of hypersync, Odin call it over drive sync, Yongnuo call it supersync and Commlite/Ojecoco call it HS Flash Mode, Pixel King just says it syncs at all speeds and has no timing adjustment and Cactus does not support this. Many of these can also be used to activate the pulsed High Speed Sync found in many hot shoe flashguns.

4 One of the important things to be noted is that there are no industry standard terms for different methods and often many names for the same method so people should be forgiven for getting confused, including suppliers. Add to this the Chinglish instruction books and confusion is to be expected. It would be great if people could use High Speed Sync (HSS) for the pulsed light and Hypersync for long tail as these are the most commonly used terms for the 2 methods. High Speed Flash Some of the newer flash systems entering the market are quoting flash speeds as short as 1/20,000 this should not be confused with high speed sync. When using flash the image is actually subject to 2 exposures, that exposed by ambient light and that exposed by flash. As an example for fill flash the majority of the exposure is from ambient and just a bit of flash. The expression dragging the shutter is used where slower shutter speeds are used to allow in more ambient to balance areas illuminated by flash. Hypersync and HSS are not designed to be used to freeze action but rather to light for the duration of the exposure and therefore will still capture movement; obviously as the shutter speed gets faster more motion will be frozen. If we consider a totally dark room i.e. no ambient then only light from the flash will illuminate the subject. It is in these circumstances where high speed flash can be used to freeze motion due to the very short pulse of light, regardless of shutter duration which will be at X-sync or slower. Why we need these solutions This shot at Sunset in August by Brian Muir is a perfect example of why we need Hypersync or HSS. If Brian had shot at the cameras meter reading the sky would have been washed out and to get these saturated colours you need to under expose by 1.5 or 2 stops which could have been done in a number of ways. Closing the aperture was not an option as he wanted the limited depth of field of f2.8 so another choice is to use a shorter exposure i.e. instead of 1/400 he selected 1/1600. By using a Yongnuo 622N trigger system along with a Lencarta Safari Li-ION he could make use of the long tail to then light the model. And record the ambient as he wished.

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