Light is vital to photography. Without it, we wouldn’t have photographs. Our sensors would just be recording blackness. Personally, I’ve always been a fan of making my own light. Mostly with flash, and mostly on location. This has meant that I’ve had to dip into the world of high speed sync a lot.
But what is high speed sync? And why would you want to use it? In the latest Laws of Light video, Jay P Morgan answers those questions and more.
In a nutshell, high speed sync a way to get around the issue of focal plane shutters. Basically, the mechanical focal plane shutter in a DSLR or mirrorless camera is two “curtains”. The front curtain sits in front of the sensor blocking light from hitting it. It opens up, the sensor is exposed to light, and then the rear curtain closes over the sensor to cut the light off.
But the main issue with the mechanical shutter is speed. It takes a certain amount of time to open the front curtain and then close the rear curtain. And this speed limit where the front curtain can be fully open before the rear curtain starts to close varies from around 1/160th to 1/320th shutter speeds, depending on the camera. This is what’s known as your sync speed. The maximum shutter speed at which you can use regular flash.
Beyond this, the rear curtain starts closing before the front curtain has fully opened. So, instead of exposing the entire sensor at once, a slit travels across your sensor, exposing different parts of it at slightly different times.
To get around this, some flashes offer high speed sync mode. This causes the flash to pulse throughout the duration of the exposure covering the slit as it moves across the sensor. You’re then able to shoot with flash all the way up to your camera’s maximum shutter speed.
Jay uses Dynalite Baja B6 strobes for high speed sync. I started off using high speed sync about 10 years ago when the Nikon SB-900 speedlight was released. Speedlights were all that was really available at the time, which offered HSS, so I had half a dozen of those. I’ve since switched to Godox AD200, AD360II and AD600 Pro strobes now that more powerful lights have started to gain HSS capabilities.
Besides high speed sync, there are a couple of other ways around your camera’s sync speed if you want to use flash.
One method, marketed by different brands under various names, is what’s commonly known as “tail sync”. This basically relies on having a strobe with a really slow flash duration that just stays lit for the entire duration of your shot. The strobe lights up when you take your shot and stays lit until the shot’s over. Although this can cause problems if your flash duration isn’t long enough to cover the entire exposure.
Another option is to use neutral density filters over your lens. This means you don’t have to go over your sync speed at all. But if you would have to use 1/8000th of a second to get a good ambient exposure, to bring that down to 1/250th in order to stay within your camera’s sync speed, you’d need to add 5 stops of neutral density over your lens. If you have an even slower sync speed, that’s 6 stops of neutral density.
With mirrorless cameras, this much neutral density may not be a problem, as the EVF can be brightened to still let you see the scene. But if you’re shooting a DSLR, then you may not even be able to see through the viewfinder to compose the scene or the camera’s autofocus might not be able to focus on the subject standing in shade – but it can be a good method if you want to capture some motion in the environment.
With HSS and tail sync, you’re going to lose some power and traditional metering isn’t going to work. Once you go past your sync speed, you either need a handheld meter capable of recording high speed sync (which right now is just the Sekonic L858), or you’re just judging it from the back of your camera by taking a shot and looking at the shot.
I’ve used all three methods at one point or another. But high speed sync is my go to. It’s the least hassle, especially when I’m working on location in the middle of nowhere.
