Demystifying High-Speed Sync

High-speed sync has been around for quite some time now, and has mostly been limited to speedlights. With Profoto’s recent adoption of the technology into its B1 and B2 Series lighting systems, they are signaling a change that has the potential to bring some much needed relief to the strobist community. This signal hopefully means the beginning of the end of flash sync limitations with DSLR cameras.

Patrick Hall wrote a great article outlining desires for the future of DSLR camera features, and in it one of those wishes was for sync speed limitations to be lifted. While high-speed sync (HSS) has its drawbacks, the flexibility more than makes up for the downfalls. Perhaps in the future, the drawbacks of HSS will be done away with completely and certainly the future of electronic shutters can do away with the whole problem altogether. We have to work with what we have now, so let's chat a bit about how high-speed sync works.

Basic HSS Operation

For some, how high-speed sync works is still a bit of a mystery. In the simplest terms I can, I’ll explain how the technology works.

First, you are in HSS when your shutter speed exceeds the maximum flash sync speed of your camera. For most cameras you can only get a flash to sync properly up to 1/250 second. There are some camera bodies that only have a maximum flash sync of 1/160 and some go to 1/320. If you exceed these shutter speeds with a flash that doesn’t have HSS, you will start to see black bars on your frame. These black bars are actually shadows from the shutter curtains hitting the sensor. So your flash goes off and hits the shutter curtain which casts a shadow on your sensor, and in turn your final image. 

A flash in HSS acts much like a constant light (similar to controlling ambient light: the faster your shutter speed the darker the ambient light gets) and as such you will start to lose flash power at higher shutter speeds. It basically turns your flash into a high-speed strobe light. It pulses light extremely fast and consistent while your shutter curtains are passing in front of your sensor. This pulsing is not noticeable to the human eye.

As your shutter speed gets faster and faster, the front curtain is dropping with the rear curtain quickly following behind it, creating a small open slit that is exposing the camera to light. Think of a scanner or copier machine: you see a “bar of light,” if you will, “scanning” over your piece of paper. The same is true for your camera’s sensor. See the GIFs below to see how your shutter acts in HSS. If you want all the crazy tech jargon involved with the process, you can read more in detail about high-speed sync and flash on PocketWizards website. They are a great resource for information and one of the industry leaders in flash triggers and high-speed sync.

The major drawback to HSS has always been gradual flash power loss when working in higher shutter speeds. As your shutter speed increases, you begin to lose flash power. Why this is, is simply due to the flash changing its flash duration. In short, the flash has to extend its flash duration to allow for the time to pulse light over the entire sensor area (acting like a constant light). Whereas in normal flash operation, both shutter curtains are completely open for a millisecond exposing the entire sensor at once. At normal sync speeds below 1/250, your flash only has to fire once to cover the entire sensor.

The Difference Between High-Speed Sync and HyperSync

This question comes up a lot and it can be confusing. This is a very technical subject matter, so I’ll explain it as simply as possible to the best of my knowledge, but if you want the charts, tables, and all the tech lingo, the PocketWizards article I mentioned above also explains the differences in depth.

High-Speed Sync

As mentioned above, the flash pulses light at a very fast rate to cover the sensor area at high shutter speeds, the resulting image is free of any black bars or gradients caused by shadows from the shutter curtains. There is a lot of other tech mumbo jumbo on how it works, but this is pretty much the basics of it.

HyperSync

HyperSync does not pulse light at all. Your flash acts normally which results in better overall flash power. The technology depends on very precise timing of when the flash goes off, and when the acutal light hits the sensor. They do this by actually triggering the flash to fire just a few milliseconds before the shutter curtains begin to move, so that the light from the flash arrives just as the shutter curtains are doing their dance. The drawback to this technology is that it often requires your flash to be at full power for best results, and the timings are going to vary greatly between different camera bodies and the flashes you are using, as every camera model has different shutter limitations and timings, and the same is true for your flashes. It is actually better for HyperSync to have a flash with a slower flash duration.

I have successfully synced an Elinchrom Ranger RX 1100w power pack and an "S" head with no modifier up to 1/8000 sec on a Nikon D800. However, there will be gradients (shadows from the shutter curtains) that happen across the frame; fairly easy to correct, along with black bars as well depending on the various flash and camera settings. For me, HyperSync is a good technology if you don’t have to have your light very close to the model, and don't mind being at full power. It is also good for action photographers shooting snowboarders or whatever. HyperSync just doesn’t feel as flexible to me and my needs, and the technology feels far from refined for easy use. Below is a real-world example of the gradient that can happen.

HyperSync certainly has a lot of potential and the technological feats made by PocketWizard are extremely impressive. The biggest issue is having to use your lights at full power aimed directly at the subject. There is just not a a lot of wiggle room with the system, and as I mentioned, I don't like fences. For action sports shooters this can be an exciting technology. Even for those who are doing more environmental work it can be useful as well, you will just have to correct the gradient in all the images you want to use in post, which lets be honest can be a pain and a bit of a waste of time if you can use HSS and get it right.

Positives of Using HSS

There are many positives to working in HSS, the first of which is being able to control the ambient light and shoot at a shallow depth of field. This is a big factor in my cinematic headshots, and it is a very liberating experience to shoot in: not having to worry about flash sync limitations, or the time of day. I feel like most photographers don’t want to have limitations when they are spending a lot of money on cameras and lights, and if we put a man on the moon it seems silly in 2015 that sync speeds are still a problem.

Another positive is the ability to stop action with your shutter speed instead of your flash. Common wisdom when not working in HSS says that if you want to freeze action and stay within your camera’s sync speed of 1/250, you need to have a strobe with an extremely fast flash duration. So your shutter curtains drop open, the flash pops and travels to your subject at an extremely fast rate, freezing it in the frame. This is great and has certainly been working just fine for a very long time, but if you had the choice to not have the limitation of your shutter, would you like it? My guess is yes. It is simply a matter of flexibility, and it seems silly to me to have thousands of dollars of gear only to be trapped in a box.  Shooting like this also means that you might have to routinely shoot at smaller apertures like f/8 or f/11 which means if you want the shallow depth of field, you either won’t get it, or you’ll have to use neutral density filters. This brings me to a question I get a lot.

Why Don’t You Just Use an ND Filter So You Can Have More Flash Power?

The simple answer is you certainly can. That’s how most people have been doing it for a long time. It’s fine, but also limiting, which I’ll address below.

I like working in HSS, but I do, at times, struggle with power issues with speedlights (hence why Profoto’s adoption excites me). I like to keep a simple footprint with my headshots or environmental portraits so I only ever use two speedlights: one as a key and one as a back kicker. You can obviously use multiple speedlights for more power, I just choose not to.

ND filters are fine, but you will still be limited in a couple areas. The first for me is the ability to see my subject clearly. I shoot a lot of headshots outside at very shallow depths of field (f/2.8–f/3.2), and my style depends on keeping my models in the shade and lighting them while balancing that with the ambient light. The fact that the model is going to be in the shade is going to make them at least 1 stop darker than the background. Combine that with a bright background and ND filters, and suddenly it becomes much harder for me to read my model’s expression. A headshot is all about the expression, and if I’m hindering my ability to see that, it bothers me. Now I’ve shot with 2 stop, and 3-stop ND filters, and I don’t feel too visually impaired, but it still limits me to a certain time frame in the day. If I’m running a business it certainly doesn’t make sense to have that kind of restriction (in case you haven't noticed I don't like fences). I have also done a shoot with a 6-stop ND filter, and it was extremely hard for me to read my model’s expression, along with that I also had focusing issues as my model was practically dark, and my background was very bright. While I got a great shot, I had to work a lot harder to get it, and I certainly didn’t have as many keepers as sometimes focus was shifting around. With HSS I can generally shoot at any time of day. You can also get vignette issues depending on the filter you are using, and other color shifts can happen. None of these are super common issues, but I’d like to remove any potential problems from a shoot if I can. Besides, if you didn’t have to put anything in front of your lens to get the effect you want, why would you?

I believe Profoto’s adoption will eventually kill the use of the ND filter for controlling depth of field. As more companies develop more powerful strobes with HSS, it will seem silly to even think about using an ND filter. Zach Sutton, Fstoppers resident editor and whip cracker, who is was always a huge fan of using ND filters, recently shot with the Profoto B2 in HSS and he was quoted as saying “it was a very freeing experience.”

Cons of HSS

Obviously you can guess that the biggest and possibly only drawback to using HSS is the power drop-off at higher shutter speeds. I have been shooting almost exclusively in HSS for about three solid years now and it is really the only drawback I can see, and to be honest in a lot of cases it’s not an issue, at least for me. If you are doing senior portraits, headshots, environmental shots, weddings, or things like that outside, you may have to run your speedlights at full power a lot more often, or combine speedlights in a single modifier, but generally it isn’t that big of deal.  For some shooting situations you may also still have limits to the time of day. I like to keep my key light very close to my model which works great in headshots for a soft light, and I usually don’t have many power problems due to that fact. It can be more of an issue when placing a light farther away for more environmental shots, but again, using multiple speedlights can fix this, along with simply compositing the light out in post.

A few other issues I’ve had are occasional misfires (maybe a timing issue) where the flash doesn’t register, and occasional variations of the actual flash exposure resulting in a darker exposed subject. These issues are typically not common enough for me to worry about.

Profoto’s Adoption and What It Can Mean For the Future

I don’t own any Profoto gear at the moment, but I’m hopefully going to soon. As Profoto is perhaps one of the most reputable companies in the industry, I take their adoption of HSS to mean that soon whether you buy Profoto gear or not it could signal an end to the cons listed above. 500w B1s are about 10 times the power of your average speedlight, so that’s plenty of power for almost anything I can think of using it for. The announcement from Profoto is going to hopefully push more manufacturers to get on board with the technology, which should provide more affordable solutions for those who don’t want to drop the coin on Profoto gear. There are currently some higher-powered strobes out there that are capable of HSS, and they are probably cheaper too, I just don't have any experiance with them. Having a big name like Profoto is simply a signal that the more reputable brands are taking this feature more seriously.

The only real drawback I can see with the Profoto B1 and B2 currently is you are limited on power levels when in HSS mode. This means the B1 defaults to a power range of +8–10 on Nikon, and +7–10 on Canon. The B2 similarly controls the usable power range in HSS. All this is in reference to the FAQ on their website, the quote below explains it.

To ensure a perfect exposure and a stable flash pulse, the B1 uses only the upper part of its power range when in HSS Mode. That is 7.0-10.0 for Canon and 8.0-10.0 for Nikon. For the B2 the energy range is 7-10 for both Canon and Nikon. Know that one f-stop of flash light is lost for every doubling of the shutter speed. In other words, when shooting with the extremely short shutter speeds that Profoto HSS offers, the B1 and B2 will in most cases be used at its max or near max power.

They are basically saying that if you are in HSS mode, you most likely you will be on the higher end of the power range anyway. But it would still be nice to have the capability to use the whole power range, especially considering I keep my key light very close, which means +8 power on the B1 is probably going to blow out the face, but I’m waiting to do some testing when I get my hands on a unit. This is something Profoto will hopefully address in either future firmware upgrades or in a new product. As it seems silly to restrict the usable power range if you have indeed got HSS fully working (restricting the usable power range almost sounds like their tech is a cross between HSS and HyperSync). To me this indicates Profoto may have only solved one big part of the problem, and will hopefully continue to tweak the technology to solve the usable power range issue. If we can do it with a speedlight, I’m sure they can figure it out with a higher-powered strobe. The future is exciting!

[Lead image, BTS shot, and shutter GIF's credit: Zach Sutton Photography - Used with permission. All rights reserved.]