The above image of the bee has been captured with the following camera settings.
- Shutter speed: 1/1000 second
- Aperture: f/5.6
- Lens: Nikon, 200mm, Micro
- Electronic flash using high speed synchronization
One of the major disadvantages of older cameras is the limitation of using flash at high shutter speeds, many cameras will limit the maximum shutter speed with flash to a shutter speedd range of 1/60 to 1/500 of a second. With more recent cameras and flash units this limitation has now been overcome. This option can be very important when you wish to balance the level of light from the flash and the natural daylight.
The Focal Plane Shutter
In order to understand how high speed flash synchronization works, we need some understanding as to how the camera’s focal plane shutter works.The shutter allows the light to reach the film or sensor and it will generally comprise two curtains travelling across the shutter area. At slower shutter speeds the first curtain will open and then after the shutter time delay the second curtain will close, the shutter opening remaining completely open for the exposure time. At higher shutter speeds (shutter speeds above the high speed flash synchronization speed) the second shutter curtain starts to open before the first shutter curtain has completely closed and this results in a slit travelling across the shutter opening which exposes light to the sensor or film.
When flash is used with a focal plane shutter at slower shutter speeds a single flash of light is all that is required to expose the sensor when the shutter is completely open. However when the shutter opening is a single slit travelling across the shutter opening, to get an even exposure the flash needs to fire continuously many thousands of time per second while the shutter slit is passing across the shutter opening.
High Speed Flash Synchronization
Limitation – There is a limitatation in using high speed flash synchronisation in that around one stop of flash power is lost compared to the normal flash power. However the benefits to be gained are great.
Rear Curtain Synchronization – Also high speed flash synchronization can not be used when rear curtain synchronization is set. This is when the flash is required to illuminate the subject just before the shutter closes, to create a blurred image aqnd then a frozen image at bthe end of the exposure time.
When to use High Speed Flash Synchronization
This setting can be used nearly all the time when the camera and flash is set to high speed flash synchronization, as the camera and flash will operate normally at shutter speeds below the flash synchronization speed and the high speed synchronization will kick in at shutter speeds above the normal synchronisation speed. as stated above the only time it can not operate is when you require to use rear curtain synchronization.
Benefits of High Speed Flash Synchronization
Balanced Lighting – In sunlight, high speed flash synchronization can be used to balance the lighting between the flash and natural light at high shutter speeds.
Freezing Action – High speed flash synchronization can be used at high shutter speeds 1/500 to 1/8000 of a second to freeze action.
Long Lenses – Long lenses generally require high shutter speeds and high speed flash synchronization can be used to acheive this.