Flash modes explained
For many people, flash is that horrid burst of light that ruins indoor photographs, stripping scenes of all atmosphere whenever it goes off. However, when it’s used correctly, flash can be the saviour of many an image, and shouldn’t be confined to being used in darkness. For example, a subtle burst of flash can be used to fill in shadows when shooting portraits of people with their backs to the sun. This means no more squinting, or dark shadows where the eyes should be. Instead, the flash turns what might otherwise be a silhouette into an evenly lit image. Here’s a quick guide to what you need to know…
Traditionally, the flash operates at 1/60 sec. This means that when you’re using flash, the shutter speed is set to 1/60 sec and the flash is synchronised to fire while the shutter is open. However, modern cameras take advantage of the fact that the flash duration is extremely short, and offer higher ‘sync’ speeds of around 1/200 sec or 1/250 sec.
Naturally, there’s nothing to stop you using slower shutter speeds, and this can be particularly useful for balancing the illumination of the flash with ambient lighting for a more natural look. This is often referred to as ‘slow-sync’ flash.
Rear curtain sync
Most flashes 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.
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.
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.
In fully-automatic mode, the pop-up flash fitted to most SLRs activates when light levels are low. However, in the more creative modes you can pop the flash up manually whenever you like, and use it for adding a little extra illumination. Bear in mind that you’ll be limited to shutter speeds that are the same as or lower than the flash’s maximum flash sync speed – usually 1/200 sec or 1/250 sec. Other limitations of built-in flash units include the risk of red-eye and the fact that the flash won’t fire in certain scene modes. Also, you might have to remove the hood from your lens to prevent it from casting a shadow across the image.
Having a flash fixed just above your camera is limiting, not least because it tends to create harsh shadows. Taking a hotshoe flashgun off-camera means it can be directed with more control, and if required can produce more even and flattering light. Some cameras feature wireless flash connectivity, enabling you to trigger multiple flashes wirelessly, but all SLR cameras can be fitted with an off-camera cord. These enable you to connect the flashgun to the hotshoe and fire it remotely.
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on Thursday, December 8th, 2011 at 10:59 am under Beginner.
Tags: camera tips, flash, flash photography tips, flashgun, rear curtain sync, red eye