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ON - CAMERA FLASH
Electronic flash is now the most common type of photographic lighting , and the standard unit is a portable flash that will fit on the camera body and work more or less automatically . Flash bulbs are much less used now that the elec- tronic units are reliable and fairly inexpensive .
The principle of electronic flash is an electrical discharge passed through a glass envelope ( the flash tube ) containing a gas such as xenon . This gives a rapid pulse of light , useless for seeing by , but ideal for exposing film . All that the camera needs to do is to synchronise the opening of the shutter with the flash discharge . Although the flash pulse from a portable unit is usually very fast indeed around 1 / 50,000sec - the shutter speed on a typical SLR must be considerably slower , between 1 / 60sec and 1 / 125sec on most models , and up to 1 / 250sec on a few . The reason for this is that the focal plane shutter on this kind of camera works at high speeds by passing only a narrow slit across the film . The near - instantaneous flash would expose only a narrow band - just the result if you set the shutter speed incorrectly . The ' X ' setting on the shutter speed dial is intended for electronic flash synchronization .
ABOVE Mounting the flashgun off the camera can eliminate the problem of red - eye .
LEFT Dedicated electronic flash has brought easy - to - use artificial lighting within the reach of every amateur .
Flash alternatives
Ring flash units ( TOP ) provide the even lighting necessary for macro photography . The preferred flashguns of many photo - journalists , hammerhead off- the - camera units ( ABOVE ) are available with re- chargeable battery packs ( SECOND FROM TOP ) . Although most modern guns have a bouncehead facility , the danger of red - eye is always present with hot - shoe mounted flashguns ( THIRD FROM TOP ) .
GUIDE NUMBERS
The light output of a flash can be calculated in different ways , but for portable flash the usual method is a guide number . The higher the number , the more powerful the particular number is already given by the manufacturer , although , as it is usually calculated for use indoors , where the reflections from walls and add to the light , it is worth testing the rec- ommended settings for yourself if it is not an automatic unit . Particularly if you use a flash outdoors , without any bright surroundings to help , you may find that an extra half - stop exposure is needed . Guide numbers are given either in feet or in meters ; to use them , simply divide the distance to the subject into the number and the result is the aperture setting . For example , if the guide number for the film you are using is 100 ( feet ) , and the person you are photo- graphing is standing about 12 feet away , the setting should be f8 .
DEDICATED FLASH
The easiest way of using flash is to buy a unit that is ' dedicated ' to the particular make of camera . This type of flash is linked electronically to the camera's operation , and makes full automation possible , including lens automatic flash metering with some models .
ABOVE The marked difference in power between a flash with a GN of 80 and one with a GN of 160 .
Automatic thyristor flash
In common with all electronic flash units this portable model operates by converting low voltage from the batteries into a higher voltage , and storing the charge in a capacitor . When the unit is triggered , the capacitor , with the help of a smaller trigger capacitor , discharges the stored energy in a burst , ionizing the gas in the flash tube to produce a brilliant white flash . Automatic operation is made possible by using a light - sensitive photo - cell that measures the amount of light reflected back from the subject . This is connected to a thyristor a very fast - acting electronic switch - which can cut off the supply of energy to the flash tube at any point . Modern ' dedicated ' thyristor flash guns read the flash exposure through the lens , during the exposure , but require additional contacts in the camera hot - shoe to transmit exposure information . Most dedicated flash guns come from the camera manufacturers , though an increasing number can be adapted to a variety of cameras by changing the hot - shoe connector .
Adjustable diffusing head . for different lens angles of view
Remote sensor , including photo - electric cell
Sync lead
Flash tube
Capacitor
Hot - shoe mount
Sync socket
Batteries ( Alkaline or Nickel- Cadmium )
ON - CAMERA FLASH
Electronic flash is now the most common type of photographic lighting , and the standard unit is a portable flash that will fit on the camera body and work more or less automatically . Flash bulbs are much less used now that the elec- tronic units are reliable and fairly inexpensive .
The principle of electronic flash is an electrical discharge passed through a glass envelope ( the flash tube ) containing a gas such as xenon . This gives a rapid pulse of light , useless for seeing by , but ideal for exposing film . All that the camera needs to do is to synchronise the opening of the shutter with the flash discharge . Although the flash pulse from a portable unit is usually very fast indeed around 1 / 50,000sec - the shutter speed on a typical SLR must be considerably slower , between 1 / 60sec and 1 / 125sec on most models , and up to 1 / 250sec on a few . The reason for this is that the focal plane shutter on this kind of camera works at high speeds by passing only a narrow slit across the film . The near - instantaneous flash would expose only a narrow band - just the result if you set the shutter speed incorrectly . The ' X ' setting on the shutter speed dial is intended for electronic flash synchronization .
ABOVE Mounting the flashgun off the camera can eliminate the problem of red - eye .
LEFT Dedicated electronic flash has brought easy - to - use artificial lighting within the reach of every amateur .
Flash alternatives
Ring flash units ( TOP ) provide the even lighting necessary for macro photography . The preferred flashguns of many photo - journalists , hammerhead off- the - camera units ( ABOVE ) are available with re- chargeable battery packs ( SECOND FROM TOP ) . Although most modern guns have a bouncehead facility , the danger of red - eye is always present with hot - shoe mounted flashguns ( THIRD FROM TOP ) .
GUIDE NUMBERS
The light output of a flash can be calculated in different ways , but for portable flash the usual method is a guide number . The higher the number , the more powerful the particular number is already given by the manufacturer , although , as it is usually calculated for use indoors , where the reflections from walls and add to the light , it is worth testing the rec- ommended settings for yourself if it is not an automatic unit . Particularly if you use a flash outdoors , without any bright surroundings to help , you may find that an extra half - stop exposure is needed . Guide numbers are given either in feet or in meters ; to use them , simply divide the distance to the subject into the number and the result is the aperture setting . For example , if the guide number for the film you are using is 100 ( feet ) , and the person you are photo- graphing is standing about 12 feet away , the setting should be f8 .
DEDICATED FLASH
The easiest way of using flash is to buy a unit that is ' dedicated ' to the particular make of camera . This type of flash is linked electronically to the camera's operation , and makes full automation possible , including lens automatic flash metering with some models .
ABOVE The marked difference in power between a flash with a GN of 80 and one with a GN of 160 .
Automatic thyristor flash
In common with all electronic flash units this portable model operates by converting low voltage from the batteries into a higher voltage , and storing the charge in a capacitor . When the unit is triggered , the capacitor , with the help of a smaller trigger capacitor , discharges the stored energy in a burst , ionizing the gas in the flash tube to produce a brilliant white flash . Automatic operation is made possible by using a light - sensitive photo - cell that measures the amount of light reflected back from the subject . This is connected to a thyristor a very fast - acting electronic switch - which can cut off the supply of energy to the flash tube at any point . Modern ' dedicated ' thyristor flash guns read the flash exposure through the lens , during the exposure , but require additional contacts in the camera hot - shoe to transmit exposure information . Most dedicated flash guns come from the camera manufacturers , though an increasing number can be adapted to a variety of cameras by changing the hot - shoe connector .
Adjustable diffusing head . for different lens angles of view
Remote sensor , including photo - electric cell
Sync lead
Flash tube
Capacitor
Hot - shoe mount
Sync socket
Batteries ( Alkaline or Nickel- Cadmium )
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