Aside from the topics of type or quality of light is the mere study of numbers, i.e., f-stops and intensities as they relate one light to another. The relationship of the intensity of one camera room light to another is termed Lighting Ratio. The goal of any lighting ratio is to ultimately obtain optimum quality prints from your properly exposed digital or film capture. This stems from an understanding of the unique marriage of digital/ film to paper and the limitations of each.
Ratio Lights
Fill-Light: casually known in portrait studios as the “pockets and
sockets” illuminator. A light which is non-specular and basically
non-evident. This light places an extremely important role in optimum
quality portraiture by simply raising the level of base-illumination
(within the digital or film’s exposure latitude) with a wide overall
wash of general illumination. Always of lesser intensity than the key.
Often seen as a simple bouncelight, large umbrella(s) or large soft-box
type illumination.
Key-Light: is the artistic “paint brush” of light which is constantly
being moved and meticulously adjusted to perform the important interplay
of light and shadow onto the subjects in your camera room. This light is
always capable of casting shadows, since its intensity is greater than
the fill-light. If the key light does not dominate, there are likely to
be conflicting shadows that result in confusing and incoherent lighting.
The “recipe” and interplay of these highlights and accompanying shadows
created by this light, is called Chiaroscuro in the Italian School of
Art. While no information concerning the creative employment of this
light is presented here, it goes without saying that a study of the
artistic application of this very important light in your portraiture
can be a lifelong pursuit. In creative, quality portraiture it is
generally understood, that the key light is to be a modified light;
modified by any number of methods, at the whim of the por-trait artist,
into varying forms of soft to extremely harsh light and also it is
common knowledge that the nearer the subject any size light is used, the
softer it becomes and the reverse is true. A typical working distance of
the Key Light used for head and shoulder portraiture might be 30 to 40
inches. Prudent use of the key light is an artistic endeavor.
Separator Lights
Hairlight: employed to add separation of body to background but more
importantly to add sparkle to the hair in portraiture, this light
becomes very important in low-key work, as separation is now more
critical. While small soft-box type lighting units are a popular,
contemporary application, most often the hair light(s) used are
spotlights with frennel lenses or direct, high efficiency reflector
units controlled by barn doors or snoots. Hair lights are usually
applied from high above the subject(s) and slightly to the rear or
behind, with the light being carefully adjusted or controlled as to
avoid striking the lens, vignetter sys-tem or subject’s nose. To
simplify the placement of this separator light, I occasionally recommend
that the light itself be attached (fixed) to the camera room ceiling,
permanently in place.
Background Light: often an alternative in body-background separation in
low-key work, but, most often used to simply add illumination to areas
behind the subject, providing details to a controlled interest area.
Control of this separator light is paramount to quality portraiture, as
many otherwise good attempts are ruined by the misuse of the background
light. While generally a controlled, gentle glow of illumination is
adequate, tastefully applied colored-gels, “cookies” or shadow patterns
often provide a refreshing level of energy into the otherwise mundane
background of the subject’s portrait (if that is the goal of the
artist).
Accent Light: used sparingly, if at all, to add separation, texture or
highlights to a portrait. I often refer to this effect as “portrait
chrome” . Gener-ally, this light(s) is in the form of a spot or highly
controlled directional light striking the subject obliquely from the
rear quadrant. Other names for this (these) lights would be;
“kicker-lights” or “garlic-lights” or “portrait chrome” lights “ ( a
gentle application is implied here, since a little “chrome” or “garlic”
goes a long way in any recipe).
A Word About Proper Exposure
Digital exposure has brought many new, and more accurate, methods into
our craft. An incident type flash meter, held at the subject and pointed
back towards the light in question, with either dome or flat disc
construction, is most often the approach for accurate illumination
measurement. One must re-member that internal camera meters or any
reflective meter are only accurate when the reading is directed onto a
neutral area or Gray Card. The Lite-Balance® disc or several other
products, generally provide this reading using a neutral area for
histogram (see below) linked exposure control for the critical digital
overall exposure readings. To simplify general RATIO light meter
procedures for film or digital, I recommend, for the studio, a good
flash meter with a dome (rather than a flat disc), which has built-in
cosine compensation, and is therefore very easy to simply switching off
other units and making sure stored power in the dead unit is totally
discharged.
Normal
Perfect
/Gray

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The SWPP 2008 Convention was an outstanding success,
we have 129 days to get ready for the 2009 convention - which starts on January 14, 2009
Photo Quote: Not everybody trusts paintings but people believe photographs. - Ansel Adams