![JP Seeburg B-2 Intervalometer](https://upload.wikimedia.org/wikipedia/commons/e/ea/JP_Seeburg_B-2_Intervalometer.jpg)
An intervalometer, also called an interval meter or interval timer, is a
device that measures short intervals of
time
Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to ...
. People commonly use such devices to signal, in accurate time intervals, the operation of some other device. The intervalometer measures the intermittent pulses between a starting pulse signal and an ending pulse signal, before a pulse counter measures the number of pulses released into the appropriate time interval.
For instance, an intervalometer might activate something every 30
second
The second (symbol: s) is the unit of time in the International System of Units (SI), historically defined as of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds ...
s.
Photography
Photographers
A photographer (the Greek φῶς (''phos''), meaning "light", and γραφή (''graphê''), meaning "drawing, writing", together meaning "drawing with light") is a person who makes photographs.
Duties and types of photographers
As in other ...
use intervalometers to trigger
exposures. Photographers often do this for a
time-lapse
Time-lapse photography is a technique in which the frequency at which film frames are captured (the frame rate) is much lower than the frequency used to view the sequence. When played at normal speed, time appears to be moving faster and thus ...
series, or to take or begin taking picture after a set delay.
Examples of intervalometer use in
aerial photography
Aerial photography (or airborne imagery) is the taking of photographs from an aircraft or other airborne platforms. When taking motion pictures, it is also known as aerial videography.
Platforms for aerial photography include fixed-wing aircra ...
include delaying the start of picture taking by an unattended camera until some time after takeoff and separating multiple exposures in time, and thus distance as the vehicle containing the camera travels, to obtain the 3D effect (
stereoscopy
Stereoscopy (also called stereoscopics, or stereo imaging) is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. The word ''stereoscopy'' derives . Any stereoscopic image is ...
). To obtain the 3D effect each image should have about 60% of the surface in common with either the preceding or following image. The interval is calculated as a function of the altitude and speed of the vehicle; shorter intervals for low altitude and high speed.
Often the purpose of a photographic intervalometer is to reduce the resources required either to take the pictures or post-process them as similar images could be obtained by having the camera continuously take pictures as rapidly as possible. Using an intervalometer permits restricting the pictures taken to only those with the desired content. This reduces the requirements for resources such as power and storage media (e.g. film or memory card space).
Most
digital single-lens reflex
A digital single-lens reflex camera (digital SLR or DSLR) is a digital camera that combines the optics and the mechanisms of a single-lens reflex camera with a digital imaging sensor.
The reflex design scheme is the primary difference between a ...
(DSLR) cameras are limited to 30 second or shorter exposures. An intervalometer can control long (>30 seconds) or very
long exposures (minutes or hours) using the "
Bulb
In botany, a bulb is structurally a short stem with fleshy leaves or leaf basesBell, A.D. 1997. ''Plant form: an illustrated guide to flowering plant morphology''. Oxford University Press, Oxford, U.K. that function as food storage organs duri ...
" setting. Long and very long exposures taken at night can be combined to create time-lapse animations, including
star trail
A star trail is a type of photograph that uses long exposure times to capture '' diurnal circles'', the apparent motion of stars in the night sky due to Earth's rotation. A star-trail photograph shows individual stars as streaks across the i ...
s.
Astrophotographers can use processing techniques with such exposures to create images of
deep-sky object
A deep-sky object (DSO) is any astronomical object that is not an individual star or Solar System object (such as Sun, Moon, planet, comet, etc.). The classification is used for the most part by amateur astronomers to denote visually observed fa ...
s in the
night sky
The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon.
Natural light sources in a night sky include ...
, like
nebulae
A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming region ...
and
galaxies
A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...
.
Most modern cameras include the most basic intervalometer functionality, the "self-timer". This delays the shutter release for a short time, allowing the photographer to get into the picture, for example.
In the past, intervalometers were external devices that interfaced to a camera shutter to take a picture, or series of pictures, at a set time. These sometimes used existing
remote shutter
A remote camera, also known as a trail camera or game camera, is a camera placed by a photographer in areas where the photographer generally cannot be at the camera to snap the shutter. This includes areas with limited access, tight spaces where a ...
features on cameras. Later, standalone products commonly referred to as intervalometers added capabilities beyond the basics of just measuring, and signaling, a time interval. One of the first added features was the ability to use an external event to signal the start of the time intervals. The ability to sense an external event is such a common feature of intervalometer products that many people do not distinguish between the sensing of the event and the measuring of time intervals.
What is meant when someone refers to an "intervalometer" must be determined from context. Some possibilities are: time-lapse capability (strictly an intervalometer function), sensing of a remote event, a time delay longer than what most consider the "self-timer" range, etc. Strictly speaking, an intervalometer only measures, and/or signals, time intervals.
Almost all digital cameras have basic intervalometer functions—current and elapsed times. More advanced functions are a matter of what the manufacturer chooses to implement in the camera's firmware. Functions beyond the self-timer are beginning appear in some digital cameras, and often distinguish between similar models in a camera line.
Military application
The ALE-39
countermeasures
A countermeasure is a measure or action taken to counter or offset another one. As a general concept, it implies precision and is any technological or tactical solution or system designed to prevent an undesirable outcome in the process. The fi ...
system uses intervalometers manufactured by Ledex Inc. (now part of
Johnson Electric
Johnson Electric (德昌電機控股有限公司) () is a provider of motors, actuators, motion subsystems and related electro-mechanical components for automotive, industrial and medical applications. Johnson Electric has manufacturing facili ...
) of Dayton, Ohio. The ALE-39 fires
flare
A flare, also sometimes called a fusée, fusee, or bengala in some Latin-speaking countries, is a type of pyrotechnic that produces a bright light or intense heat without an explosion. Flares are used for distress signaling, illumination, ...
s in a synchronized pattern, rapidly and with great reliability. The intervalometer in the ALE-39 is essentially a
solenoid
upright=1.20, An illustration of a solenoid
upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines
A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whose ...
-actuated
rotary switch
A rotary switch is a switch operated by rotation. These are often chosen when more than 2 positions are needed, such as a three-speed fan or a CB radio with multiple frequencies of reception or "channels".
A rotary switch consists of a spindl ...
driven by a separate programmer, which gives timing intervals and channel enabling to either of one or two channels. Intervalometers that contain internal interval clocks include the Lau-68, Suu-13 and similar electromechanically sequenced switches. Safety is provided to unfired outputs by maintaining a ground connection to all except the output being selected for firing; i.e., providing an electrical pulse to the firing squib.
Bomber aircraft
A bomber is a military combat aircraft designed to attack ground and naval targets by dropping air-to-ground weaponry (such as bombs), launching torpedoes, or deploying air-launched cruise missiles. The first use of bombs dropped from an aircraf ...
can release all bombs at once ("salvo") or drop individual bombs at intervals. A bombardier who selects the latter can program an intervalometer to control the rate of bomb release, which determines how far apart they land in the target area.
Home
Common intervalometers in homes include timers that turn lights on and off at set times, or controllers for
automatic sprinkler
A fire sprinkler system is an active fire protection method, consisting of a water supply system, providing adequate pressure and flowrate to a water distribution piping system, onto which fire sprinklers are connected. Although historically on ...
system. People use these devices when they leave home for an extended period, to make it appear the home is occupied. There are also a large number of commercial and industrial applications for even such basic intervalometers.
References
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Photography equipment