Monday, 6 August 2012

Flash Synchronization

Flash synchronization also called as called ‘sync’ or ‘synchro’ is the fastest speed at which your camera's shutter and flash could work together. So put plainly it is the maximum achievable shutter speed with your flash on.

Types of Flash Synchronization
Types of Flash Synchronization

Flash units emit light in an instantaneous burst with speeds ranging from 1/1,000 second, and often as short as 1/10,000 second. That means you could use any shutter speed on your camera which is less than 1/1000 of a second. So now what limits the maximum shutter speed is the flash sync speed of your camera.

For a better understanding of the importance of flash synchronization, you need to know how the shutter of modern day DSLR’s work. Most modern day DSLR’s come with a Focal Plane Shutter. You may follow the link to the article to better understand the working of a Focal Plane Shutter.

So now we have two variables, one is a light source that emits light at 1/1000 of a second or faster and second is a set of two curtains that zip across the front of the digital sensor. When the shutter release button is pressed; the first curtain travels across the sensor exposing it to light and then the second curtain travels across it closing it. The speed at which the curtains travel is constant and the shutter speed is actually achieved by delaying the release of the second curtain.

If you need to illuminate the full frame with light from flash then you need to sync flash with the time when the first curtain has travelled and the second is yet to start. That means the whole sensor is now open to light. The fastest shutter speed that allows this to happen is called the flash synchronization speed. Theoretically it is easy to achieve, but in reality each curtain takes time to travel the width of the frame. And faster speeds are achieved by releasing the second curtain before the first has reached the end of its travel. This causes to expose the sensor through a moving slit formed by the two travelling curtains. As the duration of a flash unit is very short, if it fires while the curtains are forming a slit, then only the area of the sensor uncovered by the shutter curtains at that exact moment will receive the flash light and the rest of the frame stays dark.

Photo By Adam

So flash could be made to sync with your camera at any speed equivalent or less than your camera’s sync speed. Sync speed varies with each model of camera and most modern DSLR’s sync anywhere from 1/200 to 1/500 depending upon the model. Most point and shoots sync up to 1/500.

One important fact to remember while using flash to illuminate your subjects is that the shutter speed setting for any shot actually has no effect on the exposure as far as illumination from the flash is concerned. The flash duration will be always shorter than the exposure time, so you cannot control the light from the flash using shutter speed. So remember when using flash, aperture value is what controls the flash exposure and shutter speed value is what controls the ambient light; Different combinations of flash and ambient light gives the creative photographer endless opportunities via a variety of lighting situations.

In the next article we will discuss about Photography - Lighting - Flash - Types of Flash Synchronization

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