The Wonders of Flash Page 5

Normally, fill flash should be weaker than the main light source, so it just lightens the shadows. If the "fill-flash" is too strong, it will eliminate the shadows and produce an unnatural look. Photo by Ron Leach

With backlighting, the fill-flash should balance the background exposure, thus keeping the subject from appearing in silhouette. The flash also adds keylights to the subject's eyes, giving them "life." Some camera/flash systems allow you to set the fill ratio. And some will automatically balance foreground and background exposures. Photo by Ron Leach

If you're shooting against a sky background, you can use "key-flash": Set the flash to overpower the ambient light by a stop, and expose for the flash. Thus, the flash-lit subject will be properly exposed, while the ambient-lit background is slightly underexposed, giving a darker, more dramatic sky. Again, some camera/flash systems let you select the fill ratio (set the flash for +1). You can also do it manually, by placing the flash at a distance that calls for one stop less exposure than the ambient light, and setting the camera for the flash-exposure aperture. This will underexpose the ambient light by one stop. Photo by Ron Leach

A bounce umbrella is an easily positioned source of soft light. Aim your flash unit at the umbrella, and the reflected light output is enlarged and thus softened as it is reflected (bounced) from the umbrella onto the subject. The umbrella's inner surface can be coated with white, silver or gold fabric. White produces soft light, silver produces harsher but still soft light, and gold produces warm soft light that's great for portraits.

A shoot-through umbrella is covered with translucent fabric. The flash unit is again aimed into the umbrella, but the umbrella is aimed at the subject—you're using light transmitted by the fabric, rather than light reflected from it. Shoot-throughs are handy when you need to position the light source very close to the subject, or are working in a room/studio with a low ceiling.

A box light (also known as a softbox) is essentially a square shoot-through umbrella. Its main advantage is that it produces square rather than umbrella-shaped catchlights in subjects' eyes.

Professional people photographers generally use two or more flash units to produce pro-looking studio portraits—a main (also called key) light, which establishes the lighting direction; a fill light, which softens the shadows; a background light, which illuminates the backdrop; and possibly a hair light coming from high and behind the subject, to add a highlight to the hair.

Generally, portraits look best if the main light is above and to one side of the camera. How far above and how far to one side (and to which side) depend on the subject and your preferences—experiment with different main-light positions and see what looks best with your subject. And while expert portrait photographers can do wonders with harsh light, it's a lot easier to work with soft light. Harsh light is produced by sources that are small relative to the subject, such as the flashtubes in shoe-mount flash units. Soft light is produced by sources that are large relative to the subject, such as flash reflected from a wall or a photographic umbrella reflector. Whatever the light source, the closer it is to the subject, the softer the light; the farther it is, the harsher the light. Here, the main light source was a fairly small umbrella reflector around 12 feet from the subjects. The resulting light is intermediate between really harsh and really soft. Photo by Lynne Eodice

Flash Characteristics
Electronic flash units produce light with a color temperature of 6000 K or thereabouts, well suited for use with daylight-balanced color films. (These films are actually balanced for 5500 K light, but that's close enough for most uses.) If your flash photos take on a slight blue cast, shooting with an amber No. 81A filter over the camera lens should solve the problem.

The short duration of the electronic flash burst (from 1/1000 for most manual units at full power and for auto units used at the far end of their distance range, to 1/30,000 or shorter for variable-power manual units set at low power and auto units used at very close range) makes electronic flash great for freezing moving subjects and for reducing the effects of subject and camera movement in close-up work. However, very short flash durations can cause reciprocity failure—a loss of film speed and, with color films, a color shift. With black-and-white and color-print films, this can be corrected when the negatives are printed, but with color-slide films, it might be wise to shoot a test roll to see what (if any) exposure and filtration corrections are needed. Film manufacturers generally publish reciprocity data for their films, which provide good starting points.

When autoflash units are used at close range or manual units are used at low power, there is excess, unused energy. Thyristor circuitry returns this unused energy to the capacitor to be used again, thereby extending battery life and producing very short recycle times. (Automatic flash units used at minimum shooting distances recycle almost instantaneously.)

Recycling time is how long it takes a flash unit to get ready to fire again after it has been discharged. How do you know when the flash unit has recycled and is ready to fire again? The ready light on the unit (or in the camera viewfinder) will glow. However, with many small flash units, the ready light comes on before the unit has reached full charge. If you shoot another flash picture as soon as the ready light comes on, your photograph may be underexposed. So it's best to wait a few seconds after the ready light comes on before shooting the next shot.

Light from a flash unit is directed forward by the built-in flash reflector. The beam is brightest in the center, weakening the farther to the sides you go. A flash unit's stated angle of coverage is useful information—it will let you know how wide a lens you can use with the flash unit. But bear in mind that objects at the edges of the photo won't be as brightly lit as objects in the center of the photo. Also, be aware that very long and very-large-diameter lenses can block a portion of the beam from a built-in or shoe-mount flash unit.