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استخدام الفلاش .. معدات وتقنيات إضافية .. المرشد خطوة بخطوة للتصوير الفوتوغرافي
Using flash
A flash unit is basically a portable , hard light source . It briefly lights a wide area , but the illumination it gives falls off rapidly with distance . There are two quite different types bulb and electronic . Bulbs are cheap to buy but can only be used once . They give a brilliant flash lasting around 1/50 sec . Electronic flash units cost more to buy but give thousands of flashes , each lasting less than 1/1000 sec . Both types are color balanced to match daylight ( see p . 146 ) .
The flash is usually briefer than the time your shutter is open , so it , not the shutter speed , determines the actual exposure time . The shutter must however be fully open at the moment the flash fires . This means you must synchronize the flash with the shutter , and with focal plane shutters , use speeds of 1/60 sec or longer , so that the complete frame is exposed .
You cannot measure the light given by a flash with a regular meter , the exposure is calculated indirectly . Guide numbers , or " factors " , supplied with the unit give you the combinations of aperture and subject distance for the correct exposure .
You can use flash on almost any subject . You can vary its position it need not be on the top of the camera and use it bounced or diffused as well as directly on the subject . It also has some special advantages . You can use it to fill - in harsh shadows or simulate sunlight . With electronic flash you can " freeze " fast movement , or even give a series of flashes during a long exposure , to create unusual effects .
Types of flash
Flashbulb
Flashbulb reflector unit
Synchronizing lead
Reflector for bounced flash
Electronic flash
Bulb flash
Flashbulbs burn brilliantly for around 1/50 sec . The illumination rises to a peak and then fades . You use a battery to fire most bulbs , but some require only the weak current generated within the shutter . The flashbulb unit fits into the " hot shoe " on the top of the camera ( see p . 29 ) or it can be plugged into the " M " socket on the camera , using the synchronizing lead , shown left . Flashbulbs are available in cubes flip - flash bars or individual bulbs such as shown left . Bulbs can be fitted into reflector units .
Electronic flash
Electronic units use batteries , and can be used in the " hot shoe " or plugged into the " X " socket , using the synchronizing lead . The flash is immediate , constant , and very brief . Units range from miniature types to large professional kinds . The intermediate unit , shown left . has a head which can be tilted to " bounce " the light . Some units read the illumination during the flash , and cut it off as soon as enough light has been given for the aperture in use .
Aperture and distance
Flash units carry guide numbers , or factors from which you calculate the correct exposure . Exposure is correct if your chosen f number multiplied by your flash - to - subject distance results in the guide number for your film speed . For example if the guide number is 110 , you can use f11 at 10 ft , f22 at 5 ft , and so on . This relationship between aperture and distance depends on the inverse square law ( see p . 111 ) .
Synchronization of flash and shutter
In the diagram below , the center disk shows when the shutter is open ; the outer ring the flash period ; and " C " when the shutter triggers the flash . A flashbulb is correctly triggered by the " M " socket , top left , allowing the bulb to burn to full power . Electronic flash fires correctly with the " X " socket , bottom left . Electronic flash fired on " M " , top right , or a flashbulb on ' X " , bottom right , fails to syn- chronize with the shutter .
Positioning the flash
The picture , right , was taken with a flash fired from on the top of the camera . It has created harsh , unnatural lighting .
The picture , below , shows the same subject , again taken with flash . The more natural lighting was achieved by pointing the flash upward to bounce it off the ceiling . Some flash heads hinge for this purpose ; others have a " bounce board " included with the unit . When using the flash indirectly you must compensate by increasing the exposure by two stops .
Fill - in flash
Flash is a useful fill - in light source when existing lighting conditions are very contrasty This happens . for example , when you are taking a subject indoors against a bright window , such as shown below left . Used carefully , fill - in flash enables you to expose for the detail through the window without underexposing and losing detail in the subject and interior below right . You can use flash in either daylight or tungsten light for black and white photo-graphy . But for color film , avoid mixing flash with tungsten light because the flash light is color balanced for daylight .
Fill - in flash is best used on the camera itself , but it is usually necessary to bounce or diffuse the illumination given by the flash to prevent double shadows from forming in the subject .
To calculate the exposure for fill - in flash , double the flash factor divide it by the subject distance , and then set the resulting f number on your camera . Now use your exposure meter to measure the brightest existing highlight area . and use the shutter speed that is shown against your calculated lens aperture . Doubling the flash factor underexposes the light given by the flash by two stops As a result the flash does not record as brightly as the existing lighting - filling - in the shadows without upsetting the balance of the natural lighting .
Lighting a dark interior
When you are photographing a dark , contrasty interior , such as shown below , you must use arti- ficial lighting to avoid under- exposing the scene , such as shown left . By firing the flash from several different positions during a long exposure you can light the whole subject without destroying the impression of natural lighting . In the picture , below right , the camera was on a tripod and the shutter set to " B " , the flash was fired from six separate points to give natural , even lighting and to bring out detail .
Reminders : exposure and artificial lighting
By taking the exposure reading carefully you can control the tonal range in the image
Measure the exposure from the most important part of the subject . An incident light reading measures the high- lights in the subject , other wise the area you read will record mid - gray .
In low lighting avoid reciprocity failure
The long exposures required in low lighting may create reciprocity failure . Adjust the aperture and reduce the film development time to over- come . this .
Artificial light can be used to simulate natural lighting or for special effects
Spotlights , photofloods , and flash , plus diffusers and reflectors are generally used to simulate natural light con- ditions . To do this consider carefully the height , direction , and quality of your light source .
The inverse square law relates distance and illumination
Doubling the distance between a lamp or flash and the subject quarters the illumination .
Flash gives hard lighting which must be synchronized with the shutter Flash gives similar lighting to single tungsten lamp . All flash must be synchronized with the shutter . With focal plane shutters use 1/60 sec or longer . Exposure is calcu- lated from the guide numbers .
Using flash
A flash unit is basically a portable , hard light source . It briefly lights a wide area , but the illumination it gives falls off rapidly with distance . There are two quite different types bulb and electronic . Bulbs are cheap to buy but can only be used once . They give a brilliant flash lasting around 1/50 sec . Electronic flash units cost more to buy but give thousands of flashes , each lasting less than 1/1000 sec . Both types are color balanced to match daylight ( see p . 146 ) .
The flash is usually briefer than the time your shutter is open , so it , not the shutter speed , determines the actual exposure time . The shutter must however be fully open at the moment the flash fires . This means you must synchronize the flash with the shutter , and with focal plane shutters , use speeds of 1/60 sec or longer , so that the complete frame is exposed .
You cannot measure the light given by a flash with a regular meter , the exposure is calculated indirectly . Guide numbers , or " factors " , supplied with the unit give you the combinations of aperture and subject distance for the correct exposure .
You can use flash on almost any subject . You can vary its position it need not be on the top of the camera and use it bounced or diffused as well as directly on the subject . It also has some special advantages . You can use it to fill - in harsh shadows or simulate sunlight . With electronic flash you can " freeze " fast movement , or even give a series of flashes during a long exposure , to create unusual effects .
Types of flash
Flashbulb
Flashbulb reflector unit
Synchronizing lead
Reflector for bounced flash
Electronic flash
Bulb flash
Flashbulbs burn brilliantly for around 1/50 sec . The illumination rises to a peak and then fades . You use a battery to fire most bulbs , but some require only the weak current generated within the shutter . The flashbulb unit fits into the " hot shoe " on the top of the camera ( see p . 29 ) or it can be plugged into the " M " socket on the camera , using the synchronizing lead , shown left . Flashbulbs are available in cubes flip - flash bars or individual bulbs such as shown left . Bulbs can be fitted into reflector units .
Electronic flash
Electronic units use batteries , and can be used in the " hot shoe " or plugged into the " X " socket , using the synchronizing lead . The flash is immediate , constant , and very brief . Units range from miniature types to large professional kinds . The intermediate unit , shown left . has a head which can be tilted to " bounce " the light . Some units read the illumination during the flash , and cut it off as soon as enough light has been given for the aperture in use .
Aperture and distance
Flash units carry guide numbers , or factors from which you calculate the correct exposure . Exposure is correct if your chosen f number multiplied by your flash - to - subject distance results in the guide number for your film speed . For example if the guide number is 110 , you can use f11 at 10 ft , f22 at 5 ft , and so on . This relationship between aperture and distance depends on the inverse square law ( see p . 111 ) .
Synchronization of flash and shutter
In the diagram below , the center disk shows when the shutter is open ; the outer ring the flash period ; and " C " when the shutter triggers the flash . A flashbulb is correctly triggered by the " M " socket , top left , allowing the bulb to burn to full power . Electronic flash fires correctly with the " X " socket , bottom left . Electronic flash fired on " M " , top right , or a flashbulb on ' X " , bottom right , fails to syn- chronize with the shutter .
Positioning the flash
The picture , right , was taken with a flash fired from on the top of the camera . It has created harsh , unnatural lighting .
The picture , below , shows the same subject , again taken with flash . The more natural lighting was achieved by pointing the flash upward to bounce it off the ceiling . Some flash heads hinge for this purpose ; others have a " bounce board " included with the unit . When using the flash indirectly you must compensate by increasing the exposure by two stops .
Fill - in flash
Flash is a useful fill - in light source when existing lighting conditions are very contrasty This happens . for example , when you are taking a subject indoors against a bright window , such as shown below left . Used carefully , fill - in flash enables you to expose for the detail through the window without underexposing and losing detail in the subject and interior below right . You can use flash in either daylight or tungsten light for black and white photo-graphy . But for color film , avoid mixing flash with tungsten light because the flash light is color balanced for daylight .
Fill - in flash is best used on the camera itself , but it is usually necessary to bounce or diffuse the illumination given by the flash to prevent double shadows from forming in the subject .
To calculate the exposure for fill - in flash , double the flash factor divide it by the subject distance , and then set the resulting f number on your camera . Now use your exposure meter to measure the brightest existing highlight area . and use the shutter speed that is shown against your calculated lens aperture . Doubling the flash factor underexposes the light given by the flash by two stops As a result the flash does not record as brightly as the existing lighting - filling - in the shadows without upsetting the balance of the natural lighting .
Lighting a dark interior
When you are photographing a dark , contrasty interior , such as shown below , you must use arti- ficial lighting to avoid under- exposing the scene , such as shown left . By firing the flash from several different positions during a long exposure you can light the whole subject without destroying the impression of natural lighting . In the picture , below right , the camera was on a tripod and the shutter set to " B " , the flash was fired from six separate points to give natural , even lighting and to bring out detail .
Reminders : exposure and artificial lighting
By taking the exposure reading carefully you can control the tonal range in the image
Measure the exposure from the most important part of the subject . An incident light reading measures the high- lights in the subject , other wise the area you read will record mid - gray .
In low lighting avoid reciprocity failure
The long exposures required in low lighting may create reciprocity failure . Adjust the aperture and reduce the film development time to over- come . this .
Artificial light can be used to simulate natural lighting or for special effects
Spotlights , photofloods , and flash , plus diffusers and reflectors are generally used to simulate natural light con- ditions . To do this consider carefully the height , direction , and quality of your light source .
The inverse square law relates distance and illumination
Doubling the distance between a lamp or flash and the subject quarters the illumination .
Flash gives hard lighting which must be synchronized with the shutter Flash gives similar lighting to single tungsten lamp . All flash must be synchronized with the shutter . With focal plane shutters use 1/60 sec or longer . Exposure is calcu- lated from the guide numbers .
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