Difference between revisions of "Understanding HyperSync and High Speed Sync"

Revision as of 08:08, 14 June 2013

This section discusses HyperSync and High Speed Sync at a basic level. Read the HyperSync section for more detailed information on how to adjust HyperSync for your configuration.

This page details how flashes function when triggered with HyperSync, High Speed Sync (or Auto FP), and at your camera's sync limit, or its x-sync speed. HyperSync and High Speed Sync/Auto-FP are not the same thing, and it's important to understand the differences as to how each method relates to your setup.

How Does a Flash Work?

A flash is designed to emit a very intense light for a short duration of time. This is done by filling a flashtube with xenon gas, and then using a charged capacitor to energize the xenon with a very high amount of electrical current. The peak has the highest amount of energy emitted (hence the name, "peak") but energy continues to be emitted at a decreasing rate so long as the xenon gas is energized.

While appearing to be instantly turned on and instantly turned off again, a flashtube can be excited for anywhere from 1 microsecond to tens of milliseconds. Most consumer flashes usually average around 1 millisecond, with some being longer, and some being shorter.

X-Sync - Flash behavior with normal sync limits

A flash directly connected to a camera

X-Sync is typically the fastest shutter speed at which your camera can trigger a flash. For most Canon cameras, this is 1/200th. For most Nikon cameras, this is 1/250th, except for a few exceptions like the D600.

A camera triggering a flash at X-sync follows this timeline:

1. The camera is triggered by the photographer. Several milliseconds of Lag Time pass. The amount of lag time varies from camera to camera.
2. The first shutter opens, exposing the digital sensor. Some microseconds of time pass. This shutter will stay open for the length of your selected shutter speed time (exposure time.)
3. The camera triggers its PC terminal and the center sync pin on the hot shoe.
4. The flash emits light for the its flash duration. This can be any amount of time, up to a few milliseconds.
5. The second curtain begins to move downwards across the sensor, closing the exposure "slit."
6. The second shutter in the camera closes and both shutters reset.

Shutter speeds faster than X-Sync typically have the first and second shutters moving at the same time, or with no delay between the first shutter fully opening and the second shutter beginning to close. This does not work with normal flash triggering because the second shutter can be moving when the flash is generating light which yields a clipped exposure.

If your flash has a very long duration, or your shutter is very slow moving, you can get clipping even at X-sync.

A Flash Triggered Remotely by a Typical Radio Trigger

Standard radio triggers can introduce bottom-frame shutter shadowing, or "clipping" in your image even at your camera's sync limit. 5D Classic 1/200th, Plus II radios

Typical radio triggers right off the center x-sync pin of your camera. Adding a typical radio trigger to the above timeline adds additional microseconds between steps 3 and 4. This additional delay moves the flash triggering moment towards the time when the second shutter will be moving. If your flash has a very long duration, or your shutter is very slow moving, you can get clipping when using a standard radio slave even at X-sync. You may have to use a slower shutter speed.

Users of the 5D series of cameras have especially noticed this, as evidenced by the example to the right.

Users of the PlusX, Plus III, or MultiMAX can select Transmit Only on their transmitter to use a smaller delay, as well as using Receive Only on a receiving Plus III to have the fastest transmission possible.

High Speed Sync

High Speed Sync (HSS), also known as Auto FP Sync, is the camera manufacturer's speedlight-only technique allows for triggering at shutter speeds faster than X-Sync. "FP" stands for "Focal Plane." When the first shutter starts to open, it is exposing the digital sensor, which is the Focal Plane. FP Sync means triggering the flash just before the focal plane is exposed rather than waiting until shutter is fully open.

HSS/Auto FP uses a pulsed light technique (instead of a normal single burst) that generates continuous light from before the first shutter begins to move until after the second shutter closes. At faster shutter speeds, both the first and second shutters are moving simultaneously, creating a moving slit across the digital sensor. Since the light appears continuous to the digital sensor, there is no clipping even at the fastest shutter speeds.

HSS/Auto FP requires a special flash like a Canon Speedlite or Nikon speedlight that is capable of performing this pulsed light technique. Studio strobes are not capable of pulsing light, a requirement for HSS/Auto FP. This method also requires special timing information from the camera that happens between the user pressing the shutter button and the camera's sensor opening. This information is communicated through the TTL pins of a camera's hot shoe. A normal studio flash or standard non-TTL flash cannot perform the light pulse technique, nor does it have the electrical connections required to use the pre-sync information from the camera's TTL hot shoe pins.

The HSS/Auto FP timeline would look like this:

1. The camera is triggered by the photographer. Several milliseconds of Lag Time pass.
2. Just before the first shutter would open, the camera sends signals through its hot shoe to the attached flash. This tells the Speedlight when to begin generating pulsed light as ...
3. The first shutter opens, exposing the digital sensor while the flash continuously pulses throughout the exposure.
4. Shortly after the first shutter moves, the second shutter begins to move. The pulsed light continues.
5. The second shutter in the camera closes and both shutters reset. The flash stops pulsing.

The pulsed light technique cannot emit as much light as a normal flash pulse as it uses a lot of energy to make the light continuous. This means that your flash must be much closer to the subject to be effective.

HyperSync

A normal, single flash pop is much more efficient at delivering light to a subject than an HSS/Auto-FP (pulsed) flash. You can have your flash farther from a subject, or deliver more light to the scene when using a normal flash, as well as use flashes that aren't even capable of pulsing light as required for HSS/Auto-FP.

HyperSync uses special information available in the TTL shoe pins to trigger a normal flash before X-Sync would occur. It does this by knowing how much time passes from these communications until X-sync. It can also eliminate the delay introduced by a typical radio trigger. This is different from the "HSS hack" in that the timing is both adjustable, and can be optimized for some flashes.

HyperSync requires a ControlTL transmitter like the Nikon MiniTT1 and FlexTT5 or Canon MiniTT1 and FlexTT5. Optimizing HyperSync Automation require a ControlTL receiver like the PowerMC2, PowerST4, or AC9 AlienBees Adapter. All transmitter HyperSync adjustments are made in the PocketWizard Utility on the HyperSync/HSS Tab. Any PocketWizard radio can be used as a receiver and be triggered from the ControlTL transmitter's HyperSync timing, but you will see the best results using a ControlTL receiver.

When using a ControlTL receiver there are two methods of using HyperSync Automation to get flash sync at faster than X-Sync shutter speeds, Highest Energy and Reduced Clipping. Most flashes generate a tall peak of light when first triggered, then that light fades down to a long tail. The two methods choose when to start the flash in relation to the camera's shutters opening.

Reduced Clipping

Reduced Clipping uses precision timing to keep hard black bars out of your images. This method may result in a gradation across the image (lighter at the bottom and darker at the top), but for many situations, the results are quite acceptable and usable.

Reduced Clipping benefits photographers:

• Shooting outdoors where the sky is a major factor in the top part of the image
• Using aperture priority in conditions that cause the shutter speed to go above X-sync
• In any situation where the full frame must be used and cropping is not an option

"Reduced Clipping" is selected on the ControlTL receiver, as shown in the section Configuring HyperSync.

• You would be using this optimized tail HyperSync Automation by choosing Reduced Clipping if you chose this option on the HyperSync/HSS Tab using a ControlTL receiver. This is the factory default setting.
• You would be able to use Reduced Clipping-style HyperSync manually with a FlexTT5 connected to your flash as a receiver by following the directions for the FlexTT5 P2 Port and trying to eliminate clipping at your highest shutter speeds.
• You can attempt to use Reduced Clipping-style HyperSync manually with a radio receiving on a Standard Channel (meaning a (Plus II, Plus III, PlusX, MultiMAX, FlexTT5 in Basic Trigger Mode), or internal PocketWizard receiver built in to your flash.) This is done by following the directions for the PocketWizard Radio Receiving on a Standard Channel section, and trying to eliminate clipping at your highest shutter speeds.

Note: We do not recommend using Speedlites for HyperSync due to both their short flash durations, and their IGBT design, which makes HyperSync feasible only at full power. HSS/Auto-FP may return more desirable results for users shooting above x-sync with Speedlites.

Read the HyperSync section for more detailed information on how to adjust HyperSync.

Highest Energy

Highest Energy uses precision timing to get as much flash energy into the image as possible above X-sync. This will reduce gradation, but can result in black bars or clipping in the frame. For many photographic situations this can yield acceptable or useful results as clipping can be cropped out of the image.

Highest Energy benefits photographers:

• Using HyperSync speeds just above your camera's x-sync speed, such at 1/500th or 1/1000th. This may not be the best choice at 1/8000th or the highest limit of your camera.
• Needing as much action stopping flash power in the image as possible (remember that for HyperSync, longer flash durations are better)
• Gathering images where gradation is not acceptable
• In any situation where cropping is an option

"Highest Energy" is selected on the ControlTL receiver, as shown in the section Configuring HyperSync.

• You would be using this optimized Highest Energy HyperSync Automation by choosing Highest Energy if you chose this option on the HyperSync/HSS Tab using a ControlTL receiver.
• You can use Highest Energy-style HyperSync manually with a non-ControlTL compatible flash by using a FlexTT5 connected to your flash as a receiver by following the directions for the FlexTT5 P2 Port and trying to put the most flash energy in the frame at lower HyperSync speeds without "clipping" visible at the bottom of your frame.
• You can attempt to use Highest Energy-style HyperSync manually with a radio receiving on a Standard Channel (meaning a Plus II, Plus III, PlusX, MultiMAX, FlexTT5 in Basic Trigger Mode), or internal PocketWizard receiver built in to your flash.) This is done by following the directions for the PocketWizard Radio Receiving on a Standard Channel section, and trying to put the most flash energy in the frame at lower HyperSync speeds without "clipping" visible at the bottom of your frame.

Note: We do not recommend using Speedlites for HyperSync due to both their short flash durations, and their IGBT design, which makes HyperSync feasible only at full power. HSS/Auto-FP may return more desirable results for users shooting above x-sync with Speedlites.

Read the HyperSync section for more detailed information on how to adjust HyperSync.

Factors to consider

There are many factors that change from flash to flash that affect the success of HyperSync.

Flash Duration

• Flash duration is a critical factor. The flash duration is the length of time from when your flashtube is initially energized to when it is no longer emitting energy. Longer flash durations are better. You may want to compare and contrast flash t.5 times from the flash's manufacturer directly to see how long or short your flash is. The t.5 times listed below come from the Ranger RX manual, for example.

Power Level

• Flash duration often changes with power level. When you are fine-tuning HyperSync, make sure to test across the flash power levels you intend to use so you can see if certain flash durations will cause clipping at any shutter speed you intend to use. For a great comparison of how important flash duration is, see the 5D Mark II results below for HyperSync with a Ranger RX Pack with an S head, and the results with a Ranger RX Pack with an A head. Both image were generated with the same pack and the same camera, but the flash duration is much, much shorter with the A head, and has a very noticeable visual effect. You can see these images and more on our Camera HyperSync results page.

Camera Choice

• Cameras with larger and slower shutter blades will make HyperSync less likely to work without noticeable gradation. Faster shutter blades, smaller sensors, or crop mode can often improve HyperSync success by minimizing gradation. This is not your camera's shutter speed setting.

Camera Communication Time

• Some cameras send signals up through their hot shoe before x-sync sooner than others. This gives the radios themselves a larger window of opportunity for adjustment, resulting in no "clipping" at the bottom of the frame, and some do not, resulting in "clipping" at the bottom of the frame.

What HyperSync results can I get with my camera and flash?

Thankfully, we've done a lot of the guess work for you, the customer, by shooting as many cameras as we can with as many ControlTL compatible flashes as we can. You can see those below. Simply click on your camera, then find the flash that you wish to use with HyperSync. There are countless combinations of flashes and cameras in the world, and only so many hours in a day, so we are constantly trying to add more and more flashes as time goes by. If you don't see a flash yet, feel free to contact us directly: http://www.pocketwizard.com/contact/inquiry/