Flash Techniques

Over the last 6 months I have been using even more flash in my photography. I bought a Canon 430EX 2 speed-light for some weddings I was photographing to assist me with enhancing my images and to use  mainly as fill in flash 


Jim my work colleague being a bit of an expert on the subject has been giving me lots of tuition on using speed-lights recently and at long last I think I have mastered these wonderful gadgets


At first I thought like everybody else,stick it on auto and fire away. Wrong, this is the worst thing you can do with such a great piece of equipment, you must learn how to use it and get to balance your flash with ambient light, the results can be amazing


It took me some time to understand the flash and learn how to use it but now I think i am reaping benefits of my studies


At first I didn't understand sync speeds but after some studying,reading and watching video's I have finally got my head around them now. I understand the science of the subject now and everything has fell into place


Here's a brief explanation of sync speeds and what they do:


Sync speed is the fastest shutter speed you can use with that flash with your camera 


When you take a picture, the shutter opens and closes to let light strike the image sensor. When it does so, the shutter is fully open for a very short time. If the shutter speed is too fast, the burst of light from the flash won't fully expose all parts of the image sensor and part of the scene won't be captured in the image. The fastest shutter speed that can be used is called the flash synchronization speed and is usually between 1/125-1/500 second. My Canon 7 D uses a sync of 1/250th sec. If you select a faster shutter speed directly or indirectly, most cameras will override you and lower it. The shutter works with two curtains, a front and rear (sometimes called first and second curtains). The shutter opens when the front curtain slides out of the way and ends when the rear curtain slides to close it. The flash fires either when the shutter first fully opens or just before it's about to close.

Shown here are some images that explain the process

(Top row) Front/first curtain sync (the usual mode) means the flash fires when the shutter's front curtain first fully opens to expose the image sensor.

• (Bottom row) Rear/second curtain sync means the flash fires just before the shutter's rear curtain starts to close to end the exposure.

A focal plane shutter opens a curtain to begin an exposure and closes a second curtain to end it. At fast shutter speeds (top) the second curtain starts to end the exposure before the first curtain has fully opened so the two curtains form a slit traveling across the image sensor. Flash would only expose the area uncovered by the slit between the two rapidly moving curtains. At the flash sync speed and slower (bottom) the second curtain doesn't start to close until the first one is fully open.