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PORTABLE FLASH
Most modern portable flash units are automatic in the sense that they contain some means of monitoring the light output and adjusting it according to the exposure that the picture needs . The simple way of doing this is for the flash to contain a light - sensitive cell that will measure the amount of light reflected back from the subject . Additional circuitry then quenches the duration of the flash as soon as a predetermined level of brightness has been reached . There are three important settings to be made when using this kind of automatic flash : the flash synchronisation speed on the camera , the film speed on the flash unit's calculator , and the lens aperture . The synchronisation speed varies between makes of camera : those with between - the - lens shutters will synchronise at any speed , while those with focal plane shutters have a limit , normally between 1/60 and 1 / 125sec , and sometimes simply marked as ' X ' . The lens aperture can be set within the limits shown on the flash unit's calculator , and these depend on the distance of the subject .
A more sophisticated , and increasingly more popular , type of automatic flash is the dedicated unit . This is specifically designed for one model of camera , and often uses the camera's own through - the - lens metering system to control the flash exposure . A warning light indicates when the flash output has been insuf- ficient .
The problem with using a flash directly from the camera is that the lighting effect tends to be flat , with only a thin edge of shadow , and that the exposure is only good for one distance . Usually , this results in underlit backgrounds , and occasionally , overexposed foregrounds . A standard answer to this is to bounce the light from the flash off the ceiling , or even off one wall . This softens and diffuses the light , as well as giving it an overhead direction . Many flash units have a swivelling head to allow just this , or the unit can be removed from the camera and aimed upwards . As the ceiling will absorb much of the light , a wider aperture is needed , by about 2 or 3 stops or even more if the ceiling is high or dark .
LEFT Gelatin filters are particularly useful when you want to colour or diffuse light from a portable flashgun , because they can be cut to shape and fitted over the flash head .
Flashguns are now available that act almost as ' seeing eye ' dogs for autofocus cameras - they send out an infrared beam that measures the camera to subject distance , and instruct the SLR's AF system accordingly ( top ) . Basic automatic flashguns ( above ) are fitted with a light - sensitive cell which ' kills ' the flash light when a sufficient exposure has been made .
Bounce Flash
BELOW The only source of illumination in this scene is from the desk lamp , the result being that much of the facial detail has been lost .
LEFT However , light from a flashgun mounted off the camera can be bounced off a suitably reflective surface to regain the detail and give a natural , balanced look to the scene .
LEFT Portable units can be employed to great effect when backlighting still life subjects . In this case , the backdrop has diffused the light from the flashgun to overcome the problems of reflections within the bottle .
PORTABLE FLASH
Most modern portable flash units are automatic in the sense that they contain some means of monitoring the light output and adjusting it according to the exposure that the picture needs . The simple way of doing this is for the flash to contain a light - sensitive cell that will measure the amount of light reflected back from the subject . Additional circuitry then quenches the duration of the flash as soon as a predetermined level of brightness has been reached . There are three important settings to be made when using this kind of automatic flash : the flash synchronisation speed on the camera , the film speed on the flash unit's calculator , and the lens aperture . The synchronisation speed varies between makes of camera : those with between - the - lens shutters will synchronise at any speed , while those with focal plane shutters have a limit , normally between 1/60 and 1 / 125sec , and sometimes simply marked as ' X ' . The lens aperture can be set within the limits shown on the flash unit's calculator , and these depend on the distance of the subject .
A more sophisticated , and increasingly more popular , type of automatic flash is the dedicated unit . This is specifically designed for one model of camera , and often uses the camera's own through - the - lens metering system to control the flash exposure . A warning light indicates when the flash output has been insuf- ficient .
The problem with using a flash directly from the camera is that the lighting effect tends to be flat , with only a thin edge of shadow , and that the exposure is only good for one distance . Usually , this results in underlit backgrounds , and occasionally , overexposed foregrounds . A standard answer to this is to bounce the light from the flash off the ceiling , or even off one wall . This softens and diffuses the light , as well as giving it an overhead direction . Many flash units have a swivelling head to allow just this , or the unit can be removed from the camera and aimed upwards . As the ceiling will absorb much of the light , a wider aperture is needed , by about 2 or 3 stops or even more if the ceiling is high or dark .
LEFT Gelatin filters are particularly useful when you want to colour or diffuse light from a portable flashgun , because they can be cut to shape and fitted over the flash head .
Flashguns are now available that act almost as ' seeing eye ' dogs for autofocus cameras - they send out an infrared beam that measures the camera to subject distance , and instruct the SLR's AF system accordingly ( top ) . Basic automatic flashguns ( above ) are fitted with a light - sensitive cell which ' kills ' the flash light when a sufficient exposure has been made .
Bounce Flash
BELOW The only source of illumination in this scene is from the desk lamp , the result being that much of the facial detail has been lost .
LEFT However , light from a flashgun mounted off the camera can be bounced off a suitably reflective surface to regain the detail and give a natural , balanced look to the scene .
LEFT Portable units can be employed to great effect when backlighting still life subjects . In this case , the backdrop has diffused the light from the flashgun to overcome the problems of reflections within the bottle .
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