The Power and Perils of High Speed Sync
One of the first things that anyone who studies flash photography learns about is that their camera has a minimum sync speed their camera can shoot at with flash attached. That is your camera’s sync speed. High-Speed Sync is the ability of specific flash systems to transcend your sync speed.
Learn more about the advantages and disadvantages of this technique and when best to apply it.
Understand Sync Speed
Sync speed is a limitation placed on all flash users, a fact of life. In the photography world, which often has few true rules, for decades the sync speed of your 35mm SLR camera was a hard and fast rule.
The sync speed is the fastest shutter speed in which the shutter in your camera is fully open when the flash fires. While it depends on the exact camera body you own, it is commonly either 1/200th or 1/250th of a second. Many modern digital SLR cameras won’t even allow the user to move the shutter speed to a faster setting when attached to a flash.
How Your Shutter Works
The reason shutter speeds need to be limited is that while the flash may appear instantaneous to our eye it actually has a duration. For standard exposures, the flash duration must be between after the first shutter curtain has finished opening and the second shutter curtain has finished closing.
For a long time, one of the special features that separated medium format photography from 35mm photography was that it didn’t suffer from those restrictions, allowing the photographer to surpass that sync speed limitation.
Control the Light by Surpassing Your Camera’s Sync Speed
When shooting in the bright sun without high-speed sync 35mm photographers using a flash would need to keep their shutter speeds at 1/200th or 1/250th or lower. This made the shallow depth of field from f-stops of f/2 or f/2.8 inaccessible. However, the introduction of high-speed sync or HSS in some modern flashes surpassed this limitation, leading many photographers to embrace this technological advancement.
©Laura Barisonzi Sony A7riv ISO 64 1/1600s f1.8
When Will You Most Benefit from Using High-Speed Sync?
Firstly: you want to shoot in an environment that has really bright ambient conditions but still gets a shallow depth of focus. For example, you’re shooting a headshot in midday but you still want the creamy bokeh of a shallow f stop such as f/1.4 or f/2. In order to leave the lens wide open, you’d often need very high shutter speeds like 1/1000 or higher.
Use Shallow Depth of Field and Highlight Your Subject
High speed sync flash can be a great perfect solution for this scenario. By lighting the subject and darkening the ambient light of the background with higher shutter speeds, you can make the subject stand out more.
Trade-Offs: With Great Power Comes Loss of Power
Flash systems that utilize high speed sync are tricking the camera and there will always be some kind of trade-off in order to get the result of higher shutter speeds. The high speed sync flash is divided into small pieces or pulses and delivers only a small piece of the flash at a time so that each portion of the sensor gets exposed as the shutter curtains travel across it.
Because of the pulsing, the higher your shutter speed the lower percentage of light from the strobe will actually be hitting your subject while your shutter is open. Even if you set your flash to full power only a small fraction of that light will actually hit the sensor while it’s open. All of these factors lead to a drastic loss of light power and one that is sometimes difficult to predict.
©Laura Barisonzi Sony A7riv ISO 160 1/1000s f3.5
Start with the Light Close to the Subject on High Power
It may surprise you how little light you get out of a high speed sync flash. I generally suggest starting with the flash at the maximum setting and placed close to the subject. This way you can be certain that the flash is indeed firing and then adjust from there.
Especially when using lower power strobes, it is common that full power will be your flash setting when shooting with HSS. Flash meters are not an accurate way to plan exposures when using high speed sync.
©Laura Barisonzi Nikon D850 ISO 100 1/500s f/2.8
Camera Settings for High-Speed Sync
If you want to set your camera to higher shutter speeds, remember that Sony and Canon have menu settings to enable HSS flash, Nikon refers to it as Auto-FP. Some flash brands require setting the transmitter HSS setting to on.
Test your High Speed Sync Settings
Results of high-speed sync flash will change depending on the model of camera, the model of strobe, transmitter, and shutter speeds. While some companies market the idea of shooting at 1/8000th, it is much more common to get successful results in the 1/1600-1/2000th shutter speed range.
Test your high speed sync settings before you are out shooting to see what your combination of gear can achieve.
©Laura Barisonzi Sony A7riv ISO 200 1/640s f/2.8
High Power Lights Deliver Better High Speed Sync Results
Depending on the time of day and ambient conditions, those who rely on speedlights or lights in the 150-300w range may not have enough power. This problem is even worse with cameras with larger sensors, i.e. an FX sensor like a Nikon D850 or Sony A7riv. When light is on full power it will also recycle more slowly.
If you do plan on using HSS, lights with a higher intensity and faster recycling at pull power such as Profoto B1x or Flashpoint AD600 pro are lights that will offer you more flexibility in terms of light placement and output.
Another challenge to keep in mind with HSS portraits is that if the subject’s eyes are sensitive to bright light, firing a flash at full power very close to the subject’s face could be uncomfortable or unpleasant for the subject.
Hyper sync is a related method to overcoming sync speed which uses Pocket Wizards. Instead of pulsing the strobe-like HSS, the flash timing is accommodated to work with the new shutter speeds. However, for those invested in systems other than Pocket Wizard, this could be an extremely pricey solution (especially as not all models of Pocket Wizards can hypersync).
Also, hyper sync has unpredictable results. Sometimes only part of the subject is illuminated and you need to crop the image to eliminate the portion the flash didn’t illuminate. (This is complicated enough to merit its own article and is constantly changing as new flash models come out).
This technique is incompatible with a lot of technology such as Profoto air remotes, Flashpoint branded remotes, and Broncolor remotes.
What About Freezing Action?
While the maximum shutter speed of most cameras is approximately 1/4000 or 1/8000, the fastest flash duration at using regular sync is much faster. That means that the duration that the flash lasts as opposed to the length the shutter is open is the factor that actually determines if action is fully frozen.
Even Though It’s Called High Speed It’s Not Best For Capturing Action
When shooting quickly moving subjects like cars or splashes, the flash duration is very important because the speed of the subject in the frame is relatively fast. In these cases, you want to use the flash with the shortest flash duration possible.
Flash duration is dependent on the output, brand, and model of the flash. When shooting with HSS, the duration of the flash is actually relatively long as it is a series of pulses. Therefore it is a relatively long flash duration and is not the best way to freeze moving subjects.
Short Flash Duration Freezes Subjects
If you are really looking to freeze moving subjects while using flash the best option is to control the light on the subject so that only the strobe light, not the ambient light is lighting them. No ambient light should be visible on the subject (ambient light is ok in the background). In this scenario, only the flash duration of the strobe will determine if the subject is fully frozen.
What Are The Alternatives To Using High-speed Sync?
If your goal in using high speed sync is to achieve shallow depth of field in a bright environment, one easy alternative is to use a neutral density filter or ND filter. This reduces exposure of the scene before you even take a photo by stopping down without changing color cast (this is why it’s called neutral density.)
The reason why the alternative use of an ND filter is a good conservative solution it’s because you can darken and control the ambient exposure to an exposure where you can use an f/2.0 or similar f stop and then add the flashback on top of that.
There will be no sacrifice of large percentages of flash power here so portable lights like the Profoto B10 or Godox AD200 which are currently very popular for their portability are more compatible with this technique.
It’s quite possible that you may start out planning to use high-speed sync on a shoot and not be able to get the result you need because you aren't getting enough power from your flash(es) at the distance you need the flash(es) to be from your subject. For that reason, I always like to have an ND filter in my bag as a backup.
©Laura Barisonzi Nikon D850 ISO 32 (LO) 1/200th s f/1.8 with ND filter
Neutral Density can Deliver Shallow Depth of Field
Even if you don’t own a neutral density filter, many photographers do own a circular polarizing filter. A polarizing filter actually reduces the exposure of the scene by up to 2 stops and can help you achieve a shallow depth of field.
To get a further reduction in exposure you can use ND filters such as 0.6 or 0.9 or greater. In ND filters a .3 filter decreases 50% of the light coming through the filter and is equivalent to a 1 stop reduction, .6 filter is equivalent to a 2 stop reduction and .9 is equivalent to a 3 stop reduction in exposure.
Up to 10 stop, ND filters are widely available. A 3 stop filter such as the Tiffen 3 stop ND filter should be sufficient to control the light in most portrait situations in the bright sun. I recommend removing your UV filter before screwing on your ND filter to avoid possible reflections.
One problem you may find when shooting with ND filters in the bright sun is difficulty with visibility. Especially when the background is several stops brighter than the subject you might have trouble seeing the subject’s face which can appear as a silhouette in the viewfinder. While this can be a challenge, it usually only happens when the background and foreground have a multistop difference in brightness.
Dial Up and Down with Variable ND
To gain even more control over the light you can use a variable ND filter which allows you to dial up or down the ND value within a certain range. This allows you to quickly change how many stops of light are being cut from your exposure without the hassle of changing filters.
©Laura Barisonzi Nikon D850 ISO 250 1/250s f/2.8 with ND filter
Of course, keep in mind that putting any type of glass in front of your lens degrades the quality of an image. That too applies when it comes to ND filters and is usually far worse in cheaper variable ND filters.
The most common aberrations in cheaper models are bad vignetting and color casts. Polar Pro Peter McKinnon’s variable ND filter is an excellent example of a high-quality variable ND filter with very little sacrifice in optical quality.
Step Down to Save Money
When purchasing an ND filter, the most cost-effective strategy is to buy just one filter which is the size of your largest lens diameter and then purchase a set of step down filters to mount the filter on your smaller lenses.
You will need one step down filter for each lens which has a different diameter size than the ND filter you purchase. While Polar Pro step down filters are pricey, they are superior to another step down filters as they have much larger grooves. These grooves make it faster to get on and off the lens and less susceptible to getting stuck as many step down rings do.
Neutral density filters are also a must-have for anyone shooting video and also incredibly useful for control of light in car photography and landscape photography. Since they have other possible uses they are definitely worth having in your kit.
In conclusion, while high-speed sync is a powerful tool to expand what modern photographers can do in bright ambient light conditions, you should use it with the understanding that it can’t fix every problem.
Those looking to truly freeze action should avoid high-speed sync settings on their flash. Remember that shooting in high-speed sync mode has its own special requirements and limitations.
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