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3-3. Shooting a Photography With an Electronic Flash

With its short duration, electronic flash (also known as a strobe) is an excellent source of artificial light for exposing both black-and-white and daylight color films and for digital imaging.

The burst of light is so brief it is easier on the eyes than bulb flash.  All electronic flash units operate on the same principle: electric energy is built up within a capacitor (condenser) and suddenly discharged through a gas-filled glass tube, thereby creating the flash.  Most units will recycle for another flash in a matter of seconds, as long as the batteries are fresh.

 

Using Electronic Flash

Set the ASA/ISO dial to match your film's rating.  For DCS operation, set ISO, white balance and focus controls according to manufacturer’s recommendations.

Attach the electronic flash unit to the camera.  This can be done by sliding the flash into a "hot shoe" or plugging a "PC" cord from the flash into the camera's "PC" plug.  Since different cameras have different arrangements for hot shoes and PC plugs, you should refer to the camera's instructions.

Check the flash unit batteries.  (Normally, camera manufacturer instructions list procedures for checking the batteries.  In normal use, as the batteries lose strength, the recycle time between flashes greatly increases.)

Set the flash to the proper film speed/ISO setting.   Set the flash in either automatic or manual mode.  Since every manufacturer's flash unit is different, read the instructions for your particular flash.

Set the shutter speed in accordance with flash synchronization guidance in the operator's instructions (normally, 1/60th or 1/125th for a 35mm SLR).  It is usually indicated by a different colored number or a "lightning bolt" indicator.  Failing to set the correct camera shutter speed can result in loss of the picture.  Generally speaking, leaf shutters will synchronize at higher shutter speeds than focal plane shutters.  Check your owner’s manual.

Set the aperture control to the automatic mode or the setting established by the flash-to-subject distance in feet or meters, e.g., f/11 for 0-15 feet.

Turn on the flash.  Employ direct, diffused, fill or bounce-flash techniques to achieve optimum effects.

Using one of these flash techniques, you advance your film one frame, focus on the subject and depress the shutter-release button.

Check the flash's pilot lamp to check the battery charge.   (Some flash units also indicate whether the exposure and lighting was sufficient.   If the unit you are using indicates such, check this device with each exposure.)

Keep a notepad/audio tag record of caption information for each frame or sequence.  (NOTE: As a learning tool, note flash and exposure information with each frame, if possible.)

Be sure to turn the flash unit off when not in use to conserve batteries.

 

Synchronizing Camera with Electronic Flash

The camera shutter must be synchronized with the flash unit to ensure that the shutter is wide open at the instant the camera triggers the flash to fire; modern cameras automate this function.  Otherwise, only a partial exposure would result. 

On many 35mm cameras, a shutter speed of 1/60 second is set on the camera to synchronize the camera shutter with electronic flash.  Some digital cameras and advanced 35mm cameras may require exposure compensation, special mode settings or control settings; refer to the owner’s manual for specific guidance.

When electronic flash is used, there is usually no need for a fast shutter speed.  The exposure speed is governed by the extremely short duration of the intense light -- not the shutter.  However, a phenomenon known as a "ghost image" can result under certain circumstances.  If your subject is moving quickly while you take the picture and the available light is sufficient to make an exposure on the film, then you might get a flash shot which freezes the subject -- while at the same time getting an available light shot showing a much-dimmer subject in motion.   This usually happens when the available light is also relatively bright and movement is occurring.  DCS users should comply with owner’s manual procedures.   The owner’s manual provided by the manufacturer is normally the most complete and reliable source of information and operating procedures for their product. 

 

Setting the Aperture

When shooting a flash photograph using the manual flash mode, you cannot rely on the camera's meter to guide you in setting the proper aperture for the camera.  While many flash units have a calculator dial, which tells you at a glance what aperture to use for a given flash-to-subject distance, yours may not.   Therefore, you should know how to calculate an aperture setting, given a flash guide number.

The flash unit’s manufacturer provides a numerical rating, or guide number, for a specific ISO setting.  This number indicates flash strength and aids in determining the aperture setting for that ISO.  Once the guide number has been established, it will always be valid for a particular combination of camera, flash unit, and ISO.  If the flash unit has variable power and/or flash head positions, guide number tables for both feet and meters, are usually provided.  You must be certain to use the correct table for your type of distance measurement.

f/ISO

25

50

64

100

200

400

800

1000

1600

24mm

41

58

65

82

116

164

232

259

328

35mm

49

69

78

98

138

196

277

310

392

Note: This table extract (feet) is highlighted to indicate a guide number of 98 for an ISO of 100 at a flash head position of 35mm.

To find the lens aperture, divide the flash-to-subject distance into the guide number.  Example:  A flash-to-subject distance of 12 feet divided into an ISO 125 guide number of 96 (for a particular flash unit) would result in an f/8 aperture.

Guide numbers are used as guides only.  They can be changed to fit individual conditions of use.  If your color slides are too light, use a higher guide number.  If your negatives are not dense enough (too light) use a lower guide number. 

The "automatic flash" unit or auto-flash mode is easier to use.  It uses built-in photoelectric eyes.  When the burst of light from the flash unit reflects off of the subject and returns to this photoelectric eye, it shuts the flash unit off.  In effect, it "knows" when the subject has been exposed properly.  So once the proper aperture has been set (different for each type of flash unit) you need only focus and shoot.  Read the instruction booklet for the flash unit you are using.

Automatic flash units do have disadvantages and can be fooled.  The photoelectric eye really can't distinguish between the subject and any other object, which happens to be in the picture.  This can be a problem if there are any objects in the foreground and the subject is farther away.  Some subjects reflect light better than others.  That too, could throw your exposure off.  When you have the time, use manual flash settings.  But automatic can be useful when things are happening quickly.

 

Flash Techniques

Using flash techniques properly compensates for low existing light intensity.  Below are several techniques you can use.

Direct flash. When the unit is in this position, light is flashed directly to the subject.  The flash head is aimed directly at the subject.   Direct flash often results in harsh shadows, bleached-out whites and lost details.   The subject's shadow normally cannot be eliminated using this technique. The shadow can actually detract from the subject, so be careful when using direct flash.  Direct flash can make a person appear mean and cold.  In addition, a phenomenon called "red eye" can result when your subject looks straight into your direct flash. The subject's eyes will look red or pink in a color photograph.  This can be avoided by keeping the flash at least a foot or two to one side of the camera. 

Diffused flash. With the flash in a direct flash mode, open up one f/stop setting.  The flash is diffused by placing a specially made filter in front of the flash head.  Diffusion also can be achieved by using one or two layers of lens-cleaning tissue or a white handkerchief over the flash face.  As in direct flash, the subject's shadow normally cannot be eliminated.  Again, the harsh shadow tends to detract from the subject. 

Fill flash. This technique balances sunlight (or brilliant light) and shadows by illuminating the shadow areas, thus bringing out details.  This technique is used frequently, for example, to illuminate the eyes of a subject wearing a baseball cap.  Fill flash is used with another light source to eliminate or soften harsh shadows caused by intense directional light.  The guide number of a flash could come in handy when using fill flash.  A flash that is too strong or too weak might make fill flash difficult.  Refer to the flash operator instructions for specific fill flash guidance, as directions vary from one maker to the next.  With special energy saving technology, many manufacturers make units capable of limiting output power to one-half, one-quarter, one-eighth, and even one-sixteenth, with the flick of a dial.   This is useful with fill flash. 

Bounce flash. This technique uses the ceiling or walls to bounce light and cover a wide field of view.  It works best with flashes that feature tilting flash heads.  The head is rotatable from the direct-flash position (9 o'clock) to the straight-up (12 o'clock) position.  Bounce flash often requires that the photographer open up two or more f/stops to make up for light absorbed by the ceiling or walls.   You can determine the f/stop setting by determining the distance from the flash to the ceiling or wall, and then from that  point to the subject.  Add the two distances for your total distance.  Then you must consider the color and texture of the surfaces used in bouncing; darker ceilings and walls may require another f/stop.   Many flash units feature a sensor device which, in automatic mode, compensates for bounce flash by increasing the light output until the scene receives enough illumination.   The sensor measures the amount of light reflecting off the subject and adjusts the time the flash is exposed to the subject accordingly.  When using this method with a subject who has deep-set eyes, affix a plastic picnic-type spoon (concave side toward subject) to the back of the flash head with a rubber band.  This will redirect some of the flash directly to the shadow areas.  The end result will be more balanced lighting of the subject.

Split-beam flash. This method combines bounce and fill flash techniques.   A specially made bounce card is attached to the head of the flash in its bounce flash setting.  Light is directed off the card and also off the ceiling or wall and to the subject.  This technique produces an evenly illuminated background and subject, as well as soft shadows.  It is widely used by modern photojournalists.

Open flash. Open flash is used to evenly light large dark areas.   At night, or anywhere there is little ambient light, you can open a camera shutter (with the camera on a tripod) and leave it open while you fire the flash several times to cover the entire area.  The shutter is set to "B" and the f/stop according to the guide number (the flash is not attached to the camera body).

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