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Glossary
Photographic Equipment
A Glossary of Flash Terminology
Almost all camera manufacturers have adapted their particular terminology
and ways of describing many of the entries contained in this glossary. The
terms that follow are defined based on standard Nikon School definitions,
and some terms are particular to Nikon cameras, equipment, and photographic
technology.
AF Assist Illuminator
Autofocus systems require sufficient light and contrast to operate
effectively. An AF assist illuminator provides the necessary light and
contrast when ambient conditions are not sufficient for autofocus
operation. AF assist illuminators generally operate automatically,
without requiring any additional action by the photographer. The AF
assist illuminator''s light will not appear in the picture. A useful
feature for photography in very dim light or total darkness.
Angle of Flash Coverage
The measurement in degrees of the angle formed by lines projecting from
the center of the flash to the extremities of the field of coverage.
Generally expressed by referring to focal length coverage. Uniform,
edge-to-edge illumination is very important when photographing subjects
in low-contrast ambient light.
Automatic Balanced Fill-Flash (Nikon)
A type of TTL auto flash operation which uses the camera''s exposure
meter to control ambient light exposure settings, integrated with flash
exposure control. This enables flash exposure to be kept in balance with
the overall and background brightness of the scene.
Automatic Balanced Fill-Flash with TTL Multi Sensor (Nikon technology)
An automatic balanced fill-flash system using a TTL Multi Sensor to
control TTL flash output. Compared with conventional TTL auto flash
using a single-segment sensor, flash output control is greatly advanced.
There are two types of Automatic Balanced Fill-Flash with TTL Multi
Sensor -- 3D Multi-Sensor Balanced Fill-Flash and Multi-Sensor Balanced
Fill-Flash. One or the other is available, depending on the speedlight
and lens in use.
Center-Weighted Fill-Flash
A fill-flash technique that uses the camera''s center-weighted meter for
ambient light exposure measurement. Ambient exposure is based on the
brightness of the subject from which the center-weighted meter reading
is taken, while the camera''s flash exposure control automatically
controls flash illumination to achieve the fill- flash effect. By
pointing the center-weighted area at different parts of the picture, the
photographer can select the desired brightness level. Camera-controlled
EV compensation and speedlight-controlled compensation can affect
fill-flash results. Recommended when the photographer wants to control
the ambient light exposure. For more information, refer to Matrix and
Spot Fill-Flash.
Fill-Flash
A technique that uses flash illumination as a supplement to ambient
light. Useful when photographing subjects that are backlit, with very
high-contrast lighting or in shadow. For a natural-looking effect, a
technique called "balanced fill-flash" is required. In balanced
fill-flash operation, flash output is controlled to keep it in balance
with the ambient light on the scene. Nikon offers Automatic Balanced
Fill-Flash where flash output is automatically compensated to be in
balance with the ambient light.
Flash Duration
Refers to the very short amount of time it usually takes for a flash to
fire. Automatic flash control varies the brightness by varying the
duration of the flash. Flash duration typically varies from about 1/1000
to 1/20,000 sec. for an automatic flash.
Flash Output Level Compensation
A control used to adjust an automatic TTL flash unit''s operation,
enabling an increase or decrease of flash output to lighten or darken
the flash effect.
Flash Shooting Distance Range
The distance range over which a flash can effectively provide light is
controlled by the amount of flash output available. Each automatic
speedlight''s flash output varies from maximum duration to minimum
duration. Close-up subjects will require lower (to minimum) output,
while more distant subjects will require more light up to the maximum
output. The maximum and minimum flash shooting distances that are
possible vary with the aperture in use and the maximum and minimum flash
output capability of the flash in use.
Flash Sync Speed
Normal X sync flash operation requires the entire film frame to be open
when the flash is fired. Shutter speeds at which this is possible are
referred to as the speeds at which flash sync is possible, typically
from about 1/250 sec. or slower. Varying the flash sync speed is useful
for achieving fill-flash pictures in daylight and indoor conditions.
FP High-Speed Sync (Nikon N90 and SB-25 Autofocus Speedlight only)
This feature enables flash pictures to be taken at shutter speeds higher
than the camera''s normally synchronized speeds. The flash fires
continuously at a very high cycle rate, exposing the film uniformly as
the focal plane shutter''s slit travels across the film. The light output
is moderate, with the effective output diminishing as higher shutter
speeds are used. Recommended for outdoor action photography using high
shutter speeds or for fill-flash pictures taken with wide apertures in
bright light.
Front-Curtain Sync
The flash fires an instant after the first (front) curtain of a focal
plane shutter has completed its travel across the film plane. This is
the way most cameras and flash units operate. See Rear-Curtain Sync.
Full-Open Time
With a focal-plane shutter, this indicates that the shutter is fully
open to expose the entire frame area. When a Nikon speedlight is used,
the full-open time must be longer than the momentary flash duration to
expose the entire frame. Shutter speeds that allow the entire frame
image to be exposed are referred to as flash sync speeds.
Ghost Image (or ghosting)
A double image which results from using an electronic flash in
relatively bright light with a low shutter speed. Two images, one from
the ambient light and a second from the flash, do not perfectly
coincide. Can be reduced or avoided by using higher shutter speeds.
Guide Number
The guide number indicates the power of a flash in relation to ISO film
speed. Guide numbers are quoted in either meters or feet. To convert
from meters to feet, multiply the metric number by 3.3. Guide numbers
are used to calculate the f/stop for correct exposure as follows:
f/stop=guide number/distance. Using a selected aperture, we can
calculate the required flash-to-subject distance with the formula
distance = guide number/f/stop. Useful for determining the maximum
picture-taking range for flash photography. For example, with a guide
number of 110, and an f/number of 8, the distance can be determined to
be 13 3/4 feet.
Hot Shoe
A mounting device, usually built onto the top of a camera, that enables
a flash unit, or speedlight, to be mounted on the camera. Most hot shoes
include a series of contacts that correspond to contacts on the
speedlight; these are used to control various features such as TTL flash
operation, flash sync speed and ready light activation.
Matrix Balanced Fill-Flash (Nikon technology)
A TTL automatic fill-flash system that uses the camera''s Matrix light
meter to calculate the ambient light exposure setting and then controls
the flash unit''s output with the use of the camera''s single TTL flash
sensor. Flash illumination is kept in balance with the scene''s ambient
exposure.
Monitor Pre-flash(es) (N90 with SB-25 and D-type lenses only)
Using automatic balanced fill-flash with a TTL Multi Sensor system, the
speedlight with this feature fires a series of preflashes to enable the
camera''s computer to pre-analyze the scene. The TTL Multi Sensor inside
the camera body reads the amount of reflected light, then the camera''s
microcomputer determines the area of the TTL sensor to be used for flash
output control and adjusts the flash output level. The Monitor
Pre-flashes are visible but not recognizable; they are different from
the preflashes used in Red-Eye Reduction.
Multiple Flash
Refers to the use of more than one speedlight to illuminate a subject.
The use of front light combined with side and backlight illumination
enables more creative control of lighting effects. TTL automatic flash
exposure control is possible with compatible equipment. Manual exposure
control requires complex exposure calculations.
Multi-Sensor Balanced Fill-Flash (Nikon technology)
A type of Automatic Balanced Fill-Flash that uses a TTL Multi Sensor. As
in 3D Multi-Sensor Balanced Fill-Flash, the TTL Multi Sensor is used to
provide flash output control while the camera''s exposure control system
determines the background exposure. However, distance information is not
available for Multi-Sensor Balanced Fill Flash. There are two types of
Multi-Sensor Balanced Fill-Flash -- one uses Monitor Pre-flashes in the
same manner as with 3D Multi- Sensor Balanced Fill-Flash; the other uses
no Monitor Pre-flash. The type activated is determined by the speedlight
and lens (D) in use.
Non-TTL Auto Flash
The sensor built into the flash is used, rather than a camera''s TTL
flash sensor. Sensor angle is fixed, and the system requires that the
lens aperture be set at a predetermined f/stop. Useful for ...
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