Thursday, November 18, 2004

Soften artificial light

Although beautiful, natural light is preferred, let's talk about making the best of what we get.

PJs use flash. Sometimes it may be our only light source other than stars. At other times, we may need to open up shadows within a scene (fill flash at noon). However, it can look artificial and harsh if not softened.

For PJs, even light with shadows within one to two stops of the highlights is considered "soft." Strong directional light with a three-to-one or greater ratio is considered "harsh." These designations have nothing to do with focus. It's only about the characteristic qualities of light.

The point of softening light is to scatter the light rays in various directions. This allows light to ease into areas which would otherwise remain underexposed (dark) if directional light is the primary source. In effect, it reduces the impact of highlight areas while filling the shadow areas. As such, it will typically create a reduction in the effective power and exposure of the flash (make appropriate GN deductions).

Point source light
Light refracts through the atmosphere, but generally travels in straight lines from a source. Unless the light is redirected by diffusion, refraction or reflection, it will lead to higher light ratios the further it is from the point source.

In real terms this means the difference between highlights and shadows (contrast) on a subject decreases the closer it is to a direct light source. Subject contrast will increase the further it is from the light source. This doesn't mean much to folks who are working with flash on camera (and red-eye), but it is significant for major lighting schemes.

Fall off
Disclaimer: "fall off" is technically the decrease of intensity of light from a point source. I may also use it to describe divergent or stray light particles because "pixie dust" has already been overused elsewhere. ;-}

The Inverse Square Law of Light states how light will work from a point source. If we think of a flash as a firehose, we can understand the closer we are to the nozzle, the harder the water will hit us. The further away we are, the less painful it would be.

We also understand that if we walk below the main stream of water, we'll still get wet from stray water molecules.

Directed light works similarly. If a flash is aimed directly at a subject, the subject will be brightly lit. The closer the subject is to the flash, the brighter the subject will appear in relation to surrounding objects.

Furthermore, light falls onto subjects like pixie dust near the main stream of light at a lesser intensity than those objects in the main path of directed light. Instead of drenching subjects in direct light, they can be moistened by stray light particles.

Tip in
PJs use these stray light particles to "tip in" light. The method uses the Inverse Square Law and fall off to more evenly distribute light. Tipping in light is best used with TTL (through the lens) metering, but the light can be manually metered or chimped and adjusted.

Instead of directing the flash at a subject, the light is directed above or beside the subject. The stray light particles pixie dust fall onto the subject while the main flow of light bypasses the subject and is subject to normal physics for the remainder of the scene.

The end result is a subject with similar light characteristics of the background. This method can be combined with other methods below to average and soften light for the entire scene.

Softboxes both scatter and direct light simultaneously. A softbox channels and redirects light through an opaque medium such as material or plastic. The end result is a portable, wide area of scattered light from multiple directions.

Softboxes are manufactured for both large strobe and hand-held flashes. Both are extremely valuable for light control.

Bounce card
A bounce card is a simple way to reflect and redirect light. PJs can purchase extremely expensive, pre-packaged items to attach to their flashes, but a folded photo assignment and a rubber band do the same darn thing.

PJs attach a white reflector (paper, cardboard, whatever) to the back of a flash where it extends beyond the flashhead. Ideally, it curves around the flashhead and the end pitches slightly forward to reflect more light.

Instead of the flash being the point source (for light calculations), the bounce card becomes the point source while scattering light more evenly across the scene. Because each reflecting medium has a different absorption rate, it's important to test various bounce cards to get proper exposures in non-TTL mode.

Regular bounce
PJs often bounce direct light off other objects to spread and redirect light. Occasionally it will be used to move light around other larger objects (bleachers, trees, beams, etc.), but it has the same softening effect.

Total distance
For exposure calculations, the cumulative flash-to-subject distance must be considered each time light is bounced. If the distance to a ceiling is three feet and the distance from the point on the ceiling to the subject is five feet, the flash-to-subject distance is eight feet (3+5 = 8). Again, different ceiling materials and colors (see below) will affect the actual exposure, but for a white or light cream ceiling, it should be close.

Color shift
An additional problem with bouncing flash is color balance. Different color surfaces get their color by reflecting only one color and absorbing other colors from white light. The same occurs when light is bounced off this surface.

White, cream and even some pale yellow surfaces don't do much harm to the overall image. In some cases, they are actually helpful. Red, green and some brown surfaces are a nightmare for final image color balance.

Do whatever's necessary, but keep this in mind while making lighting decisions. Occasionally an alternative lighting scheme is preferable (particularly with chrome film).

A reflector is a catch-all word for any mobile bounce surface. A photo umbrella and a folded piece of paper are both reflectors. The purpose of these items is to redirect (and typically scatter) light from the point source to the subject.

Most reflectors are neutral hues from white to black. However, gold reflectors slide in and out of vogue each few years.

Although PJs may purchase fancy spring-steel reflector discs and any number of other items targeted at "rich" photographers, an economical alternative is a silver windshield sunshade (they roll up). Likewise, a piece of cardboard with some aluminum foil and tape serves the same purpose.

Again, remember to calculate the total flash to subject distance when using any reflectors (flash to reflector + reflector to subject = total flash-to-subject distance).

Omni-Bounce diffuser
PJs seem to either love or hate the Omni Bounce diffusers. It's marketed as a product which creates a bare-bulb effect from a flash. Frankly, so does a cheap plastic drinking glass or small milk jug. I suppose it's hard to look cool with a milk jug on your flash. "Take me to your leader."

Nonetheless, it's a popular device for PJs who must work with flash on camera. It's not as harsh as direct light and allows for fairly wide light coverage by extending the point source a few inches and redirecting it outward from this point.

They make a green version for fluorescent color balance and a gold one for warming effects. However they don't seem to make a tungsten-balanced one, which is honestly beyond my comprehension.

Simple diffusers
These items are effective, but don't look as cool. Simple diffusers include handkerchiefs, wax paper, bubble wrap or any other semi-opaque diffusion materials. Recalculate the guide number for each new diffuser to ensure proper exposures.

Caution: Do not use flammable diffusers with powerful strobes or at least have a fire extinguisher handy.

Enough for now,

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