LESSON 61
Flash in depth
TTL, manual, high-speed sync, bounce, off-camera.
IN THIS LESSON
- Sync and the shutter
- TTL or manual
- High-speed sync and rear curtain
- Bouncing the light
- In practice: off-camera flash
Sync and the shutter
Flash sync means firing the flash at the moment the shutter lets light reach the sensor. The camera tells the flash when to fire through contacts in the hot shoe or through a PC sync cable. Most interchangeable-lens cameras use a focal-plane shutter, made of two curtains. At fast speeds the second curtain starts closing before the first has fully opened, so only a moving slit is exposed, and a brief flash would light only a strip. The fastest speed at which the whole frame is open at once is the X-sync speed. The source gives 1/60 or slower as typical, with some cameras reaching 1/500.
TTL or manual
Through-the-lens flash metering lets the camera set the flash power. On digital cameras it works by preflash: just before the exposure, the flash fires a small burst of known strength, the camera measures what comes back through the lens, and it calculates the power for the main flash. Canon calls its system E-TTL and later E-TTL II; Nikon uses i-TTL. It is quick and adapts as you move. In manual flash you set the power yourself, usually as a fraction of full power, and it stays the same from frame to frame. Our practice advice: TTL when distances keep changing, manual when the set is fixed and you want repeatable results.
High-speed sync and rear curtain
To use flash at shutter speeds faster than X-sync, some flashes offer high-speed sync. Instead of one burst, the unit fires a rapid series of smaller pulses across the whole time the slit travels, so every part of the sensor gets light even though the shutter is never fully open. The cost, in practice, is much less power and range. It is useful for fill flash in bright sun with a wide aperture. Rear-curtain sync, also called second-curtain sync, fires the flash just before the shutter closes, so a moving subject leaves a streak behind it and ends sharp, which reads as forward motion.
Bouncing the light
A small flash pointed straight at a face gives hard light, bright skin and dark backgrounds. Bounce flash turns walls and ceilings into large reflectors. The source explains that light bounced off walls looks like light from a large window, and light bounced off a ceiling resembles fluorescent tubes, which can look flat, like an overcast day. It suggests keeping bounced light a little weaker than the room's own light when you want a natural interior, so either can fill the other. Lesson 08 covers the basics of flash; this lesson goes further.
In practice: off-camera flash
This section is working practice. Taking the flash off the camera, on a stand or in a friend's hand, lets you choose the angle of the light, which is what shapes a face. Trigger it with a radio system, the camera's built-in wireless control, or a sync cable. Start with one flash at about 45 degrees to the side and a little above the subject, in a small softbox or umbrella. Set the camera to manual and choose the background brightness with shutter speed and the subject's brightness with flash power. Change one at a time. A gel that matches room light keeps colour consistent.
Try it today
- 01Find your camera's X-sync speed in its manual.
- 02Photograph a friend indoors with direct flash, then bounced off a white ceiling, then off a side wall.
- 03Switch the flash to manual and set it at 1/8 power; adjust only by moving it.
- 04Outdoors in bright sun, turn on high-speed sync and use a wide aperture for fill.
- 05Try rear-curtain sync at 1/8 second on a moving subject in dim light.