What is flash sync? Your flash modes and when to use them (free cheat sheet)

How your flash modes work: free photography cheat sheet from Digital Camera World

What is rear curtain sync?

Most flashguns work in what’s known as ‘front curtain’ mode. The term itself is a hangover from film days, but it basically means that the flash fires just after the shutter opens.

Rear curtain sync is a flash menu option that will fire the flash at the end of the exposure, just before the shutter closes.

To understand what this means in practical terms, imagine shooting a car coming towards you at night using a long shutter speed of, say, three seconds.

Front curtain flash would illuminate the car for an instant at the beginning of the exposure, after which only the light trails would register as the car moved across the frame; the result would be an image with a stream of lights stretching out in front of the car.

Rear curtain flash, on the other hand, would illuminate the car for an instant at the very end of the exposure, after the car and its lights had moved across the frame. The result would be a much more natural-looking image, with the light trails stretching out behind the car.

What is rear curtain sync? Digital Camera World explains

What is red-eye reduction?

Red-eye is caused by light from the flash reflecting off the red blood vessels at the back of a person’s eyes and into the lens. Red-Eye flash mode reduces the problem by firing pulses of light just before the main flash, to narrow the pupils of the subject’s eyes and reduce the amount of light reflected back. In practice, however, it works poorly, if at all, and the pre-flash pulses usually make for unnatural expressions in your subjects. It’s easier to get rid of red-eye in Photoshop Elements or CS.

What is flash metering?

Through the Lens (TTL) flash metering takes much of the complexity out of calculating flash exposures. In this mode, the camera registers the amount of light falling onto the sensor during the exposure and adjusts the power of the flash accordingly. Some cameras have a flash value (FV) or flash exposure lock (FEL) button.

This is useful for getting a good overall exposure in a complex scene, as you can zoom in on the object you want to expose correctly, fire off a test flash, and the camera will remember the correct flash level.

PAGE 1: What is flash sync?
PAGE 2: Rear curtain sync, red-eye reduction and flash metering
PAGE 3: How your flash modes work (free cheat sheet)
PAGE 4: Built-in flash vs off-camera flash


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