Section II Shooting
266
The physical size of most shoe-mount flashes
does not vary greatly. Most are approximately
3″ in width and from 4″–6″ tall. Depth will vary
from 2″ to almost 4″, depending on the projection
of the flash head.
The major mechanical difference in shoe-
mount flash units is whether the flash head
is fixed at a right angle to the body, or can be
pivoted to point upward at an angle or even
straight up. See Figure 9-45. The pivoting
head provides greater flexibility, allowing the
photographer to soften the light by bouncing it
off the ceiling or another surface. A variation is
the ringlight flash, used for close-up and macro
photography. The flashtube encircles the front of
the lens, providing even, shadowless light. The
flash body containing the electronic circuitry
mounts on the hot shoe and is connected with a
flexible cable to the flashtube, Figure 9-46.
In recent years, shoe-mount electronic
flash units have become highly sophisticated,
with many automated features. The most
fully-featured products are the dedicated
flash units manufactured for use with specific
camera models (or a range of models from one
manufacturer). These units fully automate the
process of flash photography, setting the proper
aperture and shutter speed, and adjusting the
duration of the flash by reading the light at the
film plane. Because of the metering method they
use, such dedicated units are often referred to as
TTL (through-the-lens) flash systems, Figure 9-47.
TTL exposure control is more precise than the
Shoe-mount flash units
Models are available from camera
manufacturers and from third-party equipment
makers (those whose units can be used with
various camera brands). They vary in light
output, physical size, mechanical design (typically
with or without a tilting head), and degree of
automated operation.
Light output is measured scientifically in
beam candlepower-seconds (BCPS), but from
a practical photographic standpoint, the guide
number is generally used. The guide number is
calculated by the flash manufacturer and relates
the light output to the ISO rating being used. As
described in Chapter 8, Making Exposure Decisions,
the proper flash exposure is determined by
dividing the guide number by the flash-to-subject
distance to yield the proper f-stop.
Guide numbers will range, depending on
the manufacturer, from the low or mid-40s to
as high as 150 for shoe-mount units; handle-
mount flash units may have numbers as high
as 200. All of the guide numbers noted thus
far have been for distances measured in feet.
For distances in meters, the guide numbers are
just under one-third those used for feet (1 m
is equal to approximately 39″, or a bit over 3′).
Thus, a flash with a guide number of 66 for feet
has a guide number of 20 when distances are
measured in meters. Manufacturers’ catalogs or
advertisements often will list both numbers, such
as 20/66 or 36/120.
Figure 9-45. Many shoe-mounted flash units are designed with a pivoting head that can point straight forward,
straight up, or at one or more angles in between.