To understand high speed sync, we need to understand how shutters work. Most camera shutters are two curtains that open and close. I know there are some cameras with a leaf shutter but that is for a different lesson. At speeds slower than 1/125th, or 1/60th depending on your camera, the first curtain open completely before the second curtain begins to close. At faster the first curtain of the shutter opens and before it is completely open the second curtain starts to follow it and close. This means that there is no time that the sensor is open to light all at once. A small slit travels across the sensor exposing the frame it as it goes. If your strobe goes off during this time, it show a black bar at the bottom of the frame, basically the part of the image that was not exposed to the strobe flash.
High speed sync solves this problem by firing the strobe in pluses as the first curtain opens and continues to pulse until after the second curtain closes. It happens so fast that the sensor perceives the flash as continuous light.
The upside is that you can shoot at fast shutter speeds keeping your strobe synced with the camera, allowing you to shoot with a wide open aperture in bright light situations and giving you a nice shallow depth of field. You can also strobe light your subject and then crush the BG with the shutter making your subject stand out. Remember: shutter controls ambient light and we match the aperture to the power of the strobes.
Let’s look at our shoot in downtown Los Angeles. We took beautiful Angela Whitworth downtown and shot on Grand Ave. In LA you can get a permit that allows you to shoot on the street as long as you aren’t blocking traffic or the sidewalks. I am shooting on my Canon 5D Mark III, starting with a Tamron 24-70mm lens. The camera settings are ISO 320, shutter 1/500th of a second at F4.5. The key light is a medium, silver lined soft box. It will give us nice highlights on her skin. We put a full orange (CTO) on the light and I will shoot on Tungsten for my white balance. We will allow the shadow exposure to be bright enough so the shows are blue on her face.
That is it. One Baja B4 with a full CTO.
I did a few shots at the end with another light as a rim. I used the back of a mirror as a bounce board under her chin to open up some of the shadows.
I hope you learned something about high speed sync today – how it works and how you can manipulate the background light with your shutter while still getting enough light on the subject. Keep those cameras rollin’ and keep on clickin’.