High speed sync (HSS) for off camera flash has been around for a while now, but it’s really starting to become widely used with all types of photographers. It’s very popular with portrait and fashion photographers and portrait photographers working outdoors and is becoming popular with hobby photographers too.
High speed sync is also called focal plane sync.
On Nikon cameras, the camera setting for HSS is called Auto FP (FP stands for focal plane).
What is flash sync anyway?
Before we get into the details of high speed sync photography, let’s first go over what flash sync is.
Flash sync, or sync speed, is when the flash and the shutter release are synchronized. The flash fires at the same time that the shutter exposes the image sensor.
At shutter speeds below maximum flash sync, the front (first) curtain drops to expose the sensor at the same time the flash fires, then the rear (second) curtain drops to finish the exposure.
Here’s a representation of how the shutter works with normal flash sync.
What is high speed sync for?
High speed sync is for any time that you need to use a shutter speed faster than the maximum flash sync speed your camera.
The maximum flash sync speed of different cameras varies between brands:
- Sony – 1/160 – 1/250
- Canon – 1/200
- Nikon – 1/250 and 1/320
When not using HSS, if you use a shutter speed higher than the flash sync speed of your camera, you’ll get a black band on your photo.
3 times to use high speed sync:
There are three ideal situations for using HSS rather than normal flash sync:
1. High speed sync for blurry backgrounds
A great time to use HSS flash is when you’re photographing portraits outdoors during the day and you want a wide aperture.
Without HSS, you would have to either:
- Not use a wide aperture.
- Use a neutral density filter (ND filter) to bring down the exposure so that you can use a wide aperture.
The drawback of using an ND filter is that because you’re blocking light, seeing your subject and focusing can become harder. Some ND filters also have a color cast, which impacts the color of the image.
2. High speed sync when it’s too bright outside
Even if you didn’t want to blur out the background with a wide aperture, sometimes it’s just too bright outside to use normal flash sync. Remember the Sunny 16 rule of thumb (with an f-stop of f16 you can set your shutter speed to one over the ISO for an accurate exposure)?
Well at f16 and a shutter speed of 1/300 it won’t be possible to use flash without using HSS as it’ll exceed the maximum flash sync speed of your camera.
Without HSS you’ll have to:
- Overexpose the background for your subject to be correctly exposed with the light behind them, or
- photograph with the light behind you, hitting your subject straight on, which is usually unflattering.
3. High speed sync for fast action photography
Another good use of HSS is if you want to record fast action, using a fast shutter speed, and freeze it with flash. If you need a fast shutter speed and flash, you’ll need high speed sync to achieve it.
Just be aware that high speed photography uses a lot of battery power, so you flash might take longer to recycle. It will also wear the battery down faster.
How is high speed sync different?
As we’ve discovered, the big difference with HSS is that you use high speed sync at shutter speeds above your camera’s flash sync speed. This is the whole point of HSS.
The mechanics of HSS flash work differently from normal flash sync.
How high speed sync works
To create an image using HSS, the flash pulses several times during the exposure, so that it has the effect on constant light on the subject. The pulsing is far too fast for us to see, so it still looks like just one flash of light to us.
Here’s a representation of how the shutter works in high speed sync.
What’s happening inside the camera is that as the front (first) curtain starts to drop, the rear (second) curtain follows fractionally later, so there’s a tiny gap between the two curtains as they fall.
As a result, only a rolling sliver of the image is visible to the sensor at a time. While this is happening, the flash constantly pulses, lighting the subject “continuously” as the opening drops.
So, because you can increase your shutter speed so much, with HSS you can widen the aperture to blur out the background. As a result, for portraits, you can achieve a blurry background at any time of day without having to use an ND filter. This is amazing for portrait photographers!
How do you use high speed sync?
HSS flash is a two step process, just like as using normal off camera flash.
- FIRST you assess the background brightness of an image and then set your camera accordingly. The correct exposure setting depends on your style of photography.
- THEN, once you have measured the ambient light of the scene and are happy with the exposure settings, set your lighting to illuminate your subject.
Remember, shutter speed affects the ambient light. So, for a darker background (or even a black background), increase shutter speed. If you feel that the background is too dark, lower the shutter speed.
For more dramatic portraits, underexpose the background so that your subject stands out in the image. A viewer’s eye is drawn to the lightest part of an image.
Where can you use high speed sync?
You can use HSS indoors or outdoors – anytime that you need to sync flash to a shutter speed higher than your camera’s flash sync speed.
That said, most of the time HSS is used outdoors, because of the freedom it gives to use high shutter speeds and wide apertures in daylight.
What do you need for high speed sync to work?
- Flash (either speedlights or strobe lighting) that’s capable of high speed sync. For HSS to work, you need the camera to transmit HSS to flash, and for the off camera flash to have HSS capability.
- A transmitter fitted to the hotshoe of your camera to trigger the flash.
- Light modifiers for shaping and/or softening the light like various softboxes and photography umbrellas.
- I always recommend using a light meter when using lighting of any kind. It’s a quick, easy and accurate way of establishing your exposure. However, not all light meters can measure exposures at very high shutter speeds. My Sekonic L-358, for example, works up to a maximum shutter speed of 1/1000th only.
Challenges of HSS flash
Although high speed sync is incredible and brings a wonderful freedom to photographers, as with all things it does have its challenges. Because HSS flash has to fire many times during the exposure, it has to deliver a powerful burst of light with very short duration repeatedly.
The quality of the lighting equipment you use has a big impact on performance. With high end equipment, such as Profoto, you won’t face the same challenges as when working with speedlights.
Even then, as expected, high quality speedlights will perform better than cheaper speedlights.
This isn’t insurmountable, and I’m not saying you should rush out and replace your speedlights, you just need to learn to work within the restraints of the equipment you have.
Six challenges you could face when using High Speed Sync
- HSS takes a lot of power, so the higher the speed you’re syncing at, the greater the impact will be on battery life. Some lighting equipment performs better than others. Speedlights very often don’t have enough power.
- Because HSS makes the flash work so hard, your flash may become too warm and might need to shut down for a bit to cool down.
- Recycle time between flashes can be slow with different lighting equipment. Again, speedlights will require more recycle time than any other equipment.
- You could have inconsistent exposures from the flash, particularly with speedlights.
- Bare bulb is not particularly flattering, but adding a modifier reduces the light output by up to 2 stops. This in turn means the flash has to work harder.
- Distance will impact the ability of your flash to deliver enough light. Again, better quality lighting will significantly outperform speedlights.
A word of warning about HSS photography
Once you start using HSS and discover the freedom it gives to be able to capture your subject outside at any time of day without blowing out the background with wide apertures, you’ll be hooked!
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