Hypersync – Constant ISO, Aperture, Flash Power and Distance, yet varying the Shutterspeed
From my previous tests I wanted to confirm my previous observation of the effect of shutterspeed on the flash exposure, something that does not happen in traditional flash photography using shutterspeeds at or below the camera’s advertised sync speed.
So with a constant ISO of 100, aperture constant at F2.8, flashes at constant power and flash to model distance kept constant, I shot my model at shutterspeeds ranging from 1/1,000th to 1/8,000th of a second in one stop increments. As you can see from the image below the relationship with flash exposure is inverse and linear. Double the shutterspeed, and all other variables kept constant, the flash exposure, as well as the ambient exposure (obviously) drops by one stop.
As a sidebar, the reason for adding the palm leaves in the foreground was to have something at the edge of the frame that would be hit by the flash so I could see how far the dreaded shutter curtain banding was intruding into the image. And you can see the flash banding start to intrude onto the palm leaves on the right hand side of each image, especially noticeable at 1/4,000th and 1/8,000th shutterspeeds.
Hypersync – Constant ISO and Aperture, increasing Flash Power with increase in Shutterspeed
So I did another experiment to confirm it, but this time, each time I increased the shutterspeed, I increased the flash power by one stop. And as you can see in the image below, while the ambient exposure decreased linearly at 1 stop increments, the flash exposure remained constant.
So this further confirms that the flash exposure is affected in exactly the same manner as the ambient exposure …. An increase in shutterspeed above the advertised sync speed will affect the flash exposure at the same rate as it affects the ambient exposure.
And of course the banding is now way more visible with the extra flash illumination. For my use, the banding is not negatively affecting the image at shutterspeeds up to 1/2,000th but as I get above that I will need to pay attention to how I frame the image if I have any objects that will receive flash illumination in the foreground. As long as I frame the image to allow for the banding I will be able to shoot with flash all the way up to 1/8,000th of a second.
Cool – now I understand it better and kind of know what I want to do next!
We had the recent pleasure of having our stunning images of Nikki grace the pages of Playboy South Africa – April 2014 Edition! If you missed seeing those images here’s a small sample of some that we shot (some that made it and some that didn’t) for this pictorial plus some behind the scenes from the shoot! Enjoy!
Our lovely and talented make up artist, France working her magic on set!
As mentioned before in my previous blog posts regarding hypersync, my main objective was to be able to use wide open apertures around F2.8 in bright sunlight, and use flash to fill the shadows. Shooting at wide open apertures with long lenses provides the shallow depth of field that makes the model “pop” off the blurred background. But shooting at the maximum sync speed allowed by the camera, typically around 1/250th of a second, in bright sunlight, means that you have to stop the aperture down to around f8 and this unfortunately brings the background back into focus.
You can see my previous hypersync testing approach here
So after collating my previous test data I continued my testing, this time using a live model, the adorable Latvian model Diana, who was a total pleasure to shoot with and who was patient as I experimented with various settings and lighting combinations.
Determining the ambient exposure for optimum background saturation
We shot outdoors at our pool, and I started with a simple exposure test at 100 ISO and F2.8 and the shutterspeed needed to get the background saturation I wanted was 1/2,000th of a second seen in the image below.
Hypersync testing with Nikon D3x and up to 3 Alien Bees 640WS flash heads in bright sunlight
So while the sun was out, most of my shooting was done with shutter speeds in the range of 1/1,600 – 1/3,200th second. Later on a storm cloud darkened the sky and the ambient light dropped around 4 stops so I had to slow down the shutterspeed so as not to completely underexpose the background.
I started off using the Alien Bees at full power as in my earlier testing this had yielded the best results. With all three flash heads connected I found the system quite unreliable, and it was quite a process of un-plugging, re-plugging all the connections to try and get all three units to sync and fire at full power. And most bizarely, the lower shutter release on my Nikon D3x would not allow the three units to sync at all, I had to use the upper shutter release which is a pain when shooting portrait format.
With the 3 heads at full power there was a lot of flash-to-model distance adjustment going on and it definitely killed the flow. And of course I had to allow several seconds between each shot to allow the Alien Bees to fully recharge from each full power discharge. I ended up shooting way fewer images in the 3-hour shoot than I would have in my normal glamour shooting mode. This can be a good thing and a bad thing, sometimes you see something happening in the viewfinder that you just have to capture, but the flashes have not recharged, so as I say it can be a buzz kill on a shoot with a model who moves well from pose to pose.
The images below show shutter-speeds ranging from as slow as 1/1,000th all the way up to 1/2,500th of a second. I did shoot images at 1/4,000th and at 1/8,000th of a second, but the fall-off in flash illumination is dramatic, and of course the background ends up way too dark and loses the saturation and interest that I wanted to capture.
Hypersync Testing Summary to date.
I am sure you noticed the “well, sort of…” comment in my opening line. Yes, Pocket Wizards’ Hypersync functionality definitely allowed me to shoot at shutter speeds up to 4 stops faster than the maximum camera flash sync speed without any noticeable banding. And overall I am thrilled not only with the results in my limited testing to date, but I am more excited about the possibilities to brings to our studio and our customers.
However throughout the four tests I have conducted to date, the Pocket Wizard hypersync system proved to be pretty unstable, and would give widely differing results image to image. And this occurred in all four tests conducted to date. Apparently I am not the only one experiencing this phenomenon according to my reading.
Mounted on the hotshoe of my Nikon D3x I had the Pocket Wizard MiniTT1 transmitter with the AC3 Zone Controller to adjust the flash power. On the Alien Bees I had the Pocket Wizard FlexTT5 transceivers with the AC9 Alien Bees Adapter, and I had a dummy plug inserted into the sync socket to ensure that the Flashes were not firing in slave mode. All batteries were fresh and I was powering the Alien Bees direct from the mains.
I also experimented with the AC3 controller adjusting the flash outputs. This did not go well and the output was not consistent across all the flash units despite multiple corrections, plugging and unplugging. I have no idea what was causing the instability. Something that will require some more experimenting.
At this point I am not comfortable using hypersync on a commercial shoot as it is too unreliable. But I am very excited with its potential and I am hoping that I can get the system stable enough to trust it in image-critical situations.
Maybe some other shooters can comment on their own observations………..
Back to more testing trying to get to terms with Hypersync. For a long-time shooter like myself there is a lot to unlearn and relearn with this technology. For my entire pro shooting career I always relied on the simple fact that shutterspeed has no influence on the flash component of an exposure as the flash duration was always shorter than the shutter opening.
So when shooting outdoors using flash to balance the ambient light, this meant you could set your flash-to-model distance and power level and then chase the ambient light with the shutter, slowing down or speeding up as the clouds moving overhead would change the ambient light level. And when shooting models in front of sunrises and sunsets, the same would hold true. Keep the flash-to-model distance and power constant, hold the same aperture and chase the changing lighting conditions with your shutter speed.
Well, all of this worked really well when using flash with shutter speeds equal to or slower than the camera’s sync speed.
Now with the advent of HSS and Hypersync we are tricking the camera and getting the flash to sync at shutter speeds well above the camera’s advertised sync speeds.
We know that shutterspeed will affect the ambient light exposure, but with these elevated shutter speeds, the shutterspeed is now also affecting the flash illumination on the model as well, something entirely new in my shooting experience, and it is a new aspect to shooting that I have to understand and relearn.
So this round of trials is to try and understand how much the shutterspeed will affect the flash component of the exposure.
Once again I started shooting in late afternoon in full sunlight. The equipment setup is as follows
Nikon D3x with Nikon 70-200mm f2.8
Trigger is the Pocket Wizard Mini TT1 with the AC3 Zone Controller
Receiver is the Pocket Wizard TT5 with the AC9 Alien Bees Adapter
Alien Bees 640WS flash heads, all bare heads with standard reflector, no modifiers
My previous tests with Hypersync and the Alien Bees illustrated that very useable full frame flash exposure is possible up to 1/1250th of a second with this setup. I say “full frame” as with shutter speeds above 1/1,250th there was a slightly noticeable intrusion of the inevitable shutter curtain shadow banding that crept into the frame more as the shutter speed increased, making the one edge of the frame unusable.
However if you fully understand the position of the banding and are prepared to compose your image accordingly it is possible to get decent images all the way up to 1/8000th of a second, but the flash exposure is being diminished several stops by the fast shutterspeed.
Ambient Light Testing
As before, I established the desired ambient light exposure set the ISO at a constant 100, kept the Aperture at a constant F2.8 and varied the shutterspeed. Unfortunately a large cloud moved over the set as I did this so the exposures recorded are about 2 stops less than full sunlight, but the images nevertheless clearly illustrate the effect of increasing the shutterspeed on the ambient light exposure.
Single Alien Bees Main Light FULL Power
Next I put a single bare head Alien Bee 640WS light approx. 8ft from the model, slightly off-center of the camera position, on the same side as the ambient light. I did the test with the Alien Bees at full power keeping the aperture constant at F2.8 and the ISO constant at 100. Starting from 1/500th second I increased the aperture for each image, allowing the flash time to fully recharge from the full discharge each exposure. I took the shutterspeed all the way up to 1/8,000th as I wanted to see how far the shutter shadow banding intruded into the full frame with the camera in the vertical portrait position (all my previous tests were in the landscape format)
As you can see from the images, the banding only becomes noticeable at around 1/2,000th sec, and only intrudes about 10% of the frame at 1/8,000th sec. The image is fully useable without any cropping all the way up to 1/2,000th sec, but this was not the goal of the test.
What we can see is that increasing shutterspeed from 1/500th to 1/1,000th reduces both the ambient and the flash exposure by 1 stop, and there is a similar correlation from 1/1,000th to 1/2000th , from 1/2,000th to 1/4,000th and from 1/4,000th to 1/8,000th.
So many photographers have reported widely diverging results with hypersync depending on the equipment used, so while the flash exposure appears to have a linear relationship with shutterspeed, I am hesitant to just accept this.
Single Alien Bees Main Light HALF Power
I did the same test again with the Alien Bees at ½ power (controlled from the AC3 control) and the same relationship appeared to hold true but there was not enough flash illumination to make the images at the higher shutterspeed useable.
Three Alien Bees – One Main Light , Two Rim Lights, all FULL Power
This time I added two additional Alien Bees as rim lights about 10ft from the model. Because of my findings in the previous tests I limited the shutterspeed to 1/2,000th of a second. Once again the relationship of shutterspeed to flash illumination appears to be linear.
Basically, with this setup it appears that if you double the shutterspeed you will decrease the flash illumination by one stop, which ultimately means that when you end up with an underexposed subject, you will need to shorten the flash to model distance, or add additional flash units to maintain the shutterspeed.
But as you can see the results are very promising, and obviously more testing is needed prior to relying on this technique in a commercial shoot. And knowing how the banding will affect your image will allow you to use really fast shutterspeeds, as shown in this image shot at 1/4,000th second, 5 full stops faster than the maximum camera sync speed.
The next test will be with a live model using elevated shutter speeds, and getting comfortable with the affect of shutterspeed on flash exposure
Hypersync with Nikon D3x and Alien Bees B1600 Flash
Pocket Wizard’s hypersync function allows you to use flash at shutter speeds well over the standard maximum synch speed of your camera (in most cases the max flash synch speed is around 1/250th of a second).
Why do you need flash synch at speeds over 1/250th second?
Sure I know I am late to the game, but the ability to sync flash at shutter speeds well above the camera manufacturer’s flash synch speed is a huge advantage for photographers like myself. While researching the various approaches to making this work, I became very aware that most photographers yearn for more information, so in an attempt to help photographers like myself wander through the hypersync / high speed sync morass of conflicting opinion, I offer my own journey of discovery. Hopefully some of this helps.
I typically shoot outdoor glamour and this has been paying the bills for most of my life, but like most photographers I wanted to be able to shoot my models with flash outdoors at any time, including the mid day sun, but at wide apertures to create the shallow depth of field that blurs the background and makes the model pop out of the shot. But the midday sun necessitates shutter speeds way higher than the camera’s flash sync speed, even at low ISO values. So I was confined to using either early morning light with flash or typically shooting with reflectors once the sun got higher.
My typical early morning sunrise beach shots typically required shutter speeds in the range of 1/250th – 1/2,000th of a second at my preferred shooting apertures ranging between F2.8 and F4.0 at 100 ISO.
Prior High Speed Sync HSS Experiences
Several years ago I experimented with my Nikon D3x and the Nikon SB 800 and SB 900 flash heads doing the Nikon HSS high speed synch. And while I was able to get some decent exposures all the way up to 1/8,000th of a second, for the most part it was a very unsatisfactory approach for my work from many viewpoints.
Irrespective whether I was using the Nikon SU 800 as the commander unit or the SB 900 flash as the commander, the infra red signal would not transmit the signal consistently in bright sunlight
The rapid strobing in HSS robbed the units of so much power that I had to gang four SB900 flash heads together to blast through a small soft box to illuminate the model evenly and to create a somewhat larger catch light in the eyes than the tiny pin pricks that a speed light delivers.
So the ganged flash combo had to be placed very close to the model, sometimes interfering with the shot, and would sometimes provide the uneven illumination that comes from having the light source to close to the subject.
And the flash heads would over heat under any type of rapid shooting that occurs when you get in the zone.
Since the SU 800 and SB 900 infra-red signals were not reliable, I tried out the Radio Popper transceivers that convert the infra red signal to radio signal. The flash signals were transmitted way more reliably than with the SU 800 SB900 combo on its own, but the other issues above remained.
I eventually gave up on High Speed Sync for any commercial shooting but still played with it for my personal work as I love to experiment and try new things
So last year I started playing with the pocket Wizard Mini TT1 and Flex TT5 for Nikon. I wanted to see if the HSS mode was any better. The Pocket Wizard radio signal was totally reliable, the flashes fired 100% of the time even over long distances in the midday sun but sadly the power issue of the speed lights was no different and the heads had to be placed way too close to the model to make them usable.
So I put the gear away in frustration and went back to what worked for me in the past. But after a few months I felt that I should give it another try, and this time I was going to focus on Hypersync and not High Speed Sync. For those of you who are not sure of the difference between High Speed Sync and Hypersync, I suggest reading up on this as the two approaches are very different.
Hypersync technology is achieved using the Pocket Wizard radio transmitters and receivers, PLUS software to create a pre-trigger event that allows most of the illumination from a particular flash head to synchronize with the higher than normal shutter speed on a particular camera. Please note that this very dependent on the equipment used. The brand and model of flash will have an effect, as will the brand and model of camera used. You must experiment with your equipment to see what works best for you.
Hypersync Nikon D3X with Alien Bees B1600 Monolights
While the Hypersync yielded way better performance and reliability with the Nikon SB 800 and SB 900 Speedlights than with HSS, the lack of power was still the main issue. So I started experimenting with our traveling mono lights, the Alien Bees B1600’s that provide 640WS at full power. Paul C Buff has built a superb reputation with these lights by providing arguably the best customer service in the industry as well as exceptional value, and these lights have been our go-to location lights for years.
Following the instructions on the Pocket Wizard site
I updated the firmware on all my Pocket Wizard transmitters and receivers.
Using the Pocket Wizard Utility software I set up the Pocket Wizard TT1 transmitter to Hypersync ONLY.
I set up the Pocket Wizard Flex TT5 transceiver to the Reduced Clipping mode and selected the AB1600 as the flash unit. This optimizes the trigger point to get the most power out of the unit at elevated shutter speeds
Since I have the Pocket Wizard AC3 zone controller to control the power settings of the Alien Bees, I also wanted to try the AC3 out it in this test. From the Pocket Wizard Wiki I was able to determine that the AB 1600 flash allows shutter speeds up to 1,000th second with very even illumination. At shutter speeds above 1/1,000th the clipping or banding starts to become noticeable on the full frame, but can be eliminated by cropping the image if needed.
Ambient Light Test
I conducted this test in the late afternoon shooting directly into the setting sun. As I already knew that 1/1,000th of a second was achievable, I kept the ISO constant at 100, the shutterspeed constant at 1/1,000th of second and adjusted the aperture to get the most pleasing background exposure
Playing with Aperture
Everything I had read indicated that you needed to fire the flashes at full power as this gave the longest flash duration and this would provide the best illumination with the elevated shutter speeds. So the first test was conducted with the following settings
Shutter Speed 1/1,000th
Flash Power FULL
Aperture – adjusted to suit
I was specifically looking to see if there would be any banding at the 1/1,000th shutterspeed and if so would it be more noticeable at smaller apertures. As you can see from the images below, there was no detectable banding at 1/1,000th second and while the aperture selection affected the overall exposure, the smaller aperture did not yield any banding at all.
As expected, reducing the aperture reduces both the ambient light and flash exposure.
Playing with Shutter Speeds
I was so encouraged with the ability to immediately sync at 1/1,000th of a second without any banding (2 full stops faster than my Nikon D3x max flash sync speed of 1/250th ) that I decided to see for myself what the real limit would be with shutterspeed.
So this time I set my Nikon D3x camera and Alien Bees flash settings as follows
Flash Power FULL
Varying Shutter Speed
I started at 1/1,000th second and went up in full stops from there.
As you can see all the images are a bit overexposed at F2.8, full power and the flash to model distance I selected, but it did reveal the shutterspeed at which the banding becomes noticeable. There is absolutely no visible banding at the bottom of the image at 1/1,000th.
At 1/2,000th there is just a hint of imperceptible banding, but as we get to 1/4,000th and 1/8,000th it is very noticeable but in reality the banding only projects into the bottom edge of the landscape formatted images. A simple cropping of less than 10% of the image yields a very usable image will almost no detectable banding at 1/8,000th of an image. WOW.
Knowing which side of your frame will be banded and how far it will project into the image will allow me to compose the shot for cropping in such a way as to yield very acceptable shots a 1/8,000th of a second, a major breakthrough for my photography. This is very exciting.
Interesting to note. Now since we are dealing with a flash exposure that is inherently longer than the shutter speed, increasing shutter speed now not only reduces the ambient light exposure but also now reduces the flash exposure, something that must now be factored into the exposure calculations.
Playing with Flash Power and Shutter Speeds
Based on the very encouraging results I obtained at full power, I wanted to see if they would be dramatically different at lower power settings, so I immediately lowered the power to ½ power using the AC3 Zone Controller, and tried the same test, varying the shutter speeds.
So this time I set my Nikon D3x camera and the Alien Bees flash settings as follows
Flash Power ½
Varying Shutter Speed
As you can see all the banding results are almost identical to those achieved at the full power setting. There is absolutely no visible banding at the bottom of the image at 1/1,000th, but it does become noticeable as the shutter speed increases. However, once again, cropping 10% of the image yields a very usable image will almost no detectable banding at 1/8,000th of an image. WOW.
But even more important is that I now have options. The ability to reduce flash power and get great exposures at elevated shutterspeeds is HUGE. So instead of being forced to change the flash-to-model distance to get the right exposure, I now have the option of using the AC3 controller on top of the camera to reduce the flash power and this will further allow me to get more exposures from the battery.
To be honest I am more than thrilled with the results so far. More testing is needed! But remember that shooting directly into the sun will reveal all the sensor dust bunnies that you never knew you had!
Hypersync with Nikon D3x and Nikon SB 800/SB 900 flash
Pocket Wizard’s hypersync function allows you to use flash at shutter speeds well over the standard maximum synch speed of your camera (in most cameras the max flash synch speed is around 1/250th of a second).
Why do you need flash synch at speeds over 1/250th second?
So why would you want to use flash at speeds higher than 1/250th? There are many reasons, ranging from freezing action in sports photography to my case where I shoot models outdoors and I run into the typical issues all photographers face……
If you shoot the model in direct sunlight and you want to use a wide aperture to create a narrow depth of field that blurs the background and makes the model pop out of the shot, then you have to use higher shutter speeds, even at low ISO values. My typical early morning sunrise beach shots require shutter speeds in the range of 1/1,000th – 1/2,000th at my preferred shooting apertures ranging between F2.8 and F4.0 at 100 ISO. This means that you cannot use flash and you need to use reflectors to fill in the shadows.
And while approach this has worked incredibly well for me over the years there are several issues created with the reflector approach
The model has to keep her eyes closed until the moment the trigger is tripped so she does not have to stare into the bright reflector reflecting the sunlight into her otherwise silhouetted face. Keeping the model’s forehead relaxed and her eyes fully open is always a struggle in these situations
Often the wind direction is coming from the same direction as the sun, and to keep the model rimmed by the sun, you end up with her hair blowing around her face, making shooting in the that direction almost impossible.
So it would be really great to shoot at 1/2,000th of a second at f2.8 and use flash to fill in the shadows. This gets around both of the problems above as the model no longer has to deal with a bright light continuously in her face, and it also allows you to orientate the model in such a way that the wind is blowing her hair in an acceptable direction.
Hypersync vs. HSS (High Speed Sync)
There are at least two methods that allow you to use flash at higher than normal synch speeds
HSS (High Speed Synch). This essentially makes the Nikon strobes fire in continuous low power pulses, and while it works very well in most situations, the power fall off from the flash firing thousands of consecutive low power flashes means that you cannot get normal illumination from your flash. So you have to gang several flash heads together and bring the flash units very close to the model. This often results in uneven illumination and also results in overheating the flash heads if you are shooting a lot of images in quick succession. I have used HSS shooting models at high shutter speeds but the inability to pull the flash heads further back from the model to create more evenly lit model has resulted in less than ideal results, and the overheating is a real issue.
Hypersync. This technology is achieved using Pocket Wizard hardware and software to create a pre-trigger event to get most of the illumination from the flash head to synchronize with the higher than normal shutter speed. In my case I use the Nikon specific Pocket Wizard TT1 transmitters and the Pocket Wizard TT5 transceivers. Hypersync can be used with both Speedlights (Nikon, Canon flash heads etc.) and with studio lights, but note that both have to be set at FULL power (in most cases) meaning that you have no flash exposure control other than the distance of the flash to the model. In the case of studio lights, they offer way more power (WS) than speed lights, so can potentially offer substantially faster shutter speeds and allow you much greater flash to model distances and allow you to use modifiers like soft boxes that create more even illumination. However the down side to using studio lights outdoors on location is that they need a power supply (either generator or portable battery) and are heavy to drag around outdoors, and of course large light boxes are prone to blowing over in the wind so you need additional sand bags to secure the light stands. Note that in the case of studio flash units, a light with a LONGER flash duration works better in Hypersync than a flash with a shorter flash duration as the tail of the flash is better able to synch with the elevated shutter speed
TEST:- Hypersync with Nikon D3x and Nikon SB 800/SB 900 flash
In this test I am purely going to see what results I can achieve with my Nikon D3x and my Nikon SB800 and SB 900 strobes in hypersync mode. I have 6 of these but will only use 4 in this test. I wanted to do the test with the default PW settings (not adjusting any timing offsets in the software application) to see if it would work and then only make adjustments if the results were unacceptable.
I wanted to do the test at midday to deal with the harshest conditions but rain kept me inside and the test was conducted late in the afternoon. I shot at 100 ISO and F.8 with a 70-200mm lens.
First determine ambient light exposure
I first checked ambient light with no flash to determine what I considered the ideal exposure to give me the underexposed saturated background that I wanted
While I actually liked the look of the background exposure at 1/800th, I settled on 1/1250th of a second to see if I could get the flash to synch at shutter speeds that I would typically deal with in my normal early morning beach shoot scenarios.
Pocket Wizard Nikon SB900 / SB800 speed lights in Hypersync
I positioned the flash units as follows. Note that I ganged two SB 900’s as my main lights as the distance to the “model” was too close to get even illumination over the full length of the model with just one bare flash head, so I added a second head lower down on the light stand to illuminate her “legs”.
The right hand side of her face was bathed in direct afternoon light. Below you will see a couple of examples. All images were shot in landscape format. None of the images below have been edited other than the text placed over the images. They are just as they came out of the camera, no adjustment of levels, color, contrast, saturation etc. They are also shown full height so we can see if any banding occurs (bottom of frame in landscape format on Nikon cameras)
I am happy to say that I was able to get very usable results with the 4 Nikon flash heads at speeds all the way up to 1/8000th of a second at F2.8 and at F4.0. The minute I tried stopping down the aperture to F5.6 or smaller, the flash units were not able to illuminate the model adequately, so this is where the studio lights would start to come into play. I achieved these results with the default PW settings, no adjustments were made to the flash offset timing.
It is important to note that when using hypersync, in these elevated shutter speeds, the flash duration is now inherently longer than the shutter speed, so now not only does the aperture control the flash exposure, but so too does the shutter speed. This is completely different to shooting with flash at shutter speeds under the sync speed where shutter speed has not effect on the flash exposure.
This means that if you want to shoot at really high shutter speeds around 1/4000th or faster, you will have to gang several speedlights together to compensate for the reduction in illumination.
Nikon Hypersync Summary
In summary the PW TT1 and TT5 units allow you to use Hypersync with Nikon (and other brands of speedlights) at much higher than standard shutter speeds. This allows you to
freeze action in sports photography,
use wide open apertures in bright sunlight,
to overpower the sun (to a limited effect with speed lights)
to underexpose the ambient light background to create deeply saturated images.
And I encourage you to do your own testing. Do not rely on my information as all cameras and flash units behave differently in Hypersync.