What’s the Difference? is a series of video lighting tutorials. Each episode responds to a single question. In this episode, Jared Platt tries freezing motion with the High-Speed Sync. The entire series, including all videos, articles and lighting diagrams, is available here.
Here is the scenario (that is all too common): You are shooting outside on a sunny day. You are shooting with the sun behind your subject, so she is not staring into a bright ball of flame and being front lit by the harshest light in existence. This means you need to use a flash.
So you set your shutter speed between 1/125 and 1/250 of a second (depending on your camera body), you dial down your ISO to 50 or 100, and you set your aperture at the required f number for the depth of field you need.
Now it’s time to test the ambient settings you just dialed in. With a little flash, the bad lighting on the subject will be fixed. But that sky is far too bright, and so is the tree line.
This means that you need to either sacrifice your f stop, come back when it is not so bright, or pretend you meant to take a photo with a white sky. None of those options are ever really all that appealing. But thanks to High-Speed Sync, there is a fourth, much more appealing option.
With Ambient Light
This ambient exposure was taken at 1/125 sec at f 5.6 and ISO 100. It is not uncommon to find yourself in a similar situation even when using flash, as your ambient exposure remains too bright because of the sync speed requirements (1/125 – 1/250 on most cameras).
I was not going to leave my sky this bright, so something had to be done.
We brought in the sky by lowering the ISO to 50 and increasing the f number to f10. Of course, the subject would have been far too dark at those settings if we had not used our Profoto B2 and B1 Off-Camera Flashes to add some light.
The B1 (with a Zoom Reflector) was behind the bride and to the right of the frame as a hair light.
Our two B2 Off’-Camera Flashes were being employed from the right of the frame as a main light. The higher B2 was modified with a Umbrella Deep Silver M and lit her face and body. The lower B2 was bareheaded and pointed directly at the bottom of her dress.
In this image, we solved the problem of the bright white sky with our exposure changes, but there were some negative trade offs. First, motion was still a problem at 1/125 – 1/250 sec. In this case, you can see motion in the bride’s hair and in the flowers. Second, because we had to change our f-stop from f 5.6 to f 10 to capture the sky, our depth of field was far greater, giving us far too much detail in the trees and not enough separation between the subject and the background.
With High-Speed Sync
Enabling High-Speed Sync (HSS) changed the dynamics of the shot completely. Because HSS allows the flash to expose the chip evenly at higher shutter speeds, raising the shutter speed to 1/1600, 1/2500 or higher meant I could keep my aperture at f 5.6 and maintain the softer background I preferred.
The other effect of raising the shutter speed was that I was able to freeze the motion of her hair and the flowers as the bride spun around.
There is no question that sometimes we want motion and sometimes we don’t. Also, there is no correct answer to which f-stop is the correct f-stop to use in any given photograph. We all make choices that effect depth of field, movement and noise every time we take a shot, and many times there is a serious compromise that has to be made in favor of one setting or another.
But having flashes with High-Speed Sync functionality removes one layer of compromise in the image making process. Because any shutter speed is fair game.