Cameras for Time-Lapse Photography

J. Aloway, C. B. Moore, and B. Vonnegut

Motor-driven, cam-controlled cameras are particularly suitable for simple time-lapse photography.External intervalometers can be arranged to control the duration of each exposure to compensate auto-matically for widely varying light intensities.

IntroductionFew adequate and inexpensive time-lapse cameras

are available commercially. In order to study thunder-clouds, we have constructed drive and exposure controlsystems for various cameras that use film ranging in sizefrom 8 mm to 128 mm.

Initially we used the system described by Schaefer'and obtained some excellent sequences showing themotion of clouds with this method. While it has thevirtue of simplicity, use of the technique requires theclose attendance of an operator to rewind the cameradrive at least once every 10 min. In our studies wewish to photograph the thunderstorms that grow overour mountain top laboratory, therefore, we do notneed an operator and-in contrast to Schaefer's modeof operation-we do not want the direction of thecamera to be changed during the sequence. Wemerely need reliable and automatic photography witha camera aimed at a fixed arena.

In an effort to achieve these aims, we next used thecontinuous drive system developed by Vonnegut2 andinstalled several 16-mm cameras in a network surround-ing the cloud laboratory. The camera drives advancedone frame every 20 see with a nominal 3-sec exposure.Neutral density filters were placed in front of each lensto attenuate the incident light so that a satisfactoryexposure was obtained under some predetermined lightintensity. This arrangement was quite satisfactoryfor photography of clouds at a distance when they wereilluminated constantly by sunlight; we have obtainedmany kilometers of interesting cloud film exposed inthis manner from remote unmanned stations. Auto-matic time clocks were used to turn each camera on inthe morning and to turn it off 10 h later. In thismanner the interesting clouds during the daylight period

The first two authors named are with the New Mexico Instituteof Mining and Technology, Socorro, New Mexico 87801; B.Vonnegut is with SUNY, Albany, New York 12203.

Received 1 April 1970.

over a 2-day period were photographed on a standard30-m roll of 16-mm film.

With this system, however, poor photography re-sulted whenever the light level changed and-for ourthunderstorm studies-this often limited the use offixed exposure, continuous drive cameras.

Lenses with automatically controlled irises becamereadily available for 8-mm cameras several years ago;we equipped several of the smaller cameras with con-tinuous drives and with automatic lenses. Some ade-quate cloud pictures have been obtained with thesecameras but the technique is limited to the 8-mm filmand to the focal lengths of the lenses that are availablewith automatic irises.

Camera DriveTo overcome the disadvantages, for our work, of

available camera drives, we have constructed a cameradrive of a different type which uses a low-speed motor,a cam, and two switches operated by the cam. Thecam is mounted on the motor shaft which drives thecamera mechanism directly. Power to the motor ispassed through the switches which are cam-controlledin such a manner that the motor will drive the camerauntil the cam opens one of the switches which then stopsthe camera at that position until an external switchclosure is provided. One switch is set at the positionnecessary to stop the drive when the camera shutter isopen, while the other switch stops the drive when theshutter is closed. An external intervalometer providesswitch closures at predetermined time intervals whichbridge across the cam-controlled switches and causethe camera to advance film and to make exposures.This arrangement minimizes the wear and fatigue ofparts caused by rapid accelerations and abrupt stopsexperienced with solenoid drives.

The SS 25 stepping motor manufactured by SuperiorElectric Company has been particularly useful in acamera drive as its output shaft rotates once every 6

see without gear reduction and it delivers 0.17 Nm(25-in. ounce) of torque which is sufficient to advancefilm in most of our cameras. When necessary more

August 1970 / Vol. 9, No. 8 / APPLIED OPTICS 1811

torque can be obtained by use of larger motors of thistype. The motor shaft stops within about 1.50 when-ever input power ceases; this allows excellent control ofthe position of a camera shutter.

The basic motor that we use operates from 120-V60-cycle ac, but a bifilar version is available which wehave used with solid state circuitry to drive camerasfrom a low voltage battery. A camera driven in themanner described above can be arranged so that, whena brief external switch closure occurs, a short filmexposure is made, the film advances, and the motor thenstops awaiting the start of the next cycle.

We use this mode of camera operation for time-lapsephotography from the nose of an airplane that fliesaround and over thunderclouds. To minimize theeffects of aircraft motion, the cameras used here areeither Kodak Type Cin E equipped with a Genevamovement (for short exposures) or a Bolex Type H 16which advances one frame every th revolution of theexternal drive shaft.

Lightening PhotographyBy proper arrangement of external circuitry, the

camera may also be made to stop with the shutter openuntil a switch closure is provided whereupon the camerashutter closes, film is advanced, and the shutter opensagain, awaiting the next external pulse. This secondmode with normally open shutter is employed in severaldifferent ways. It is used for the photography oflightning which interests us greatly as we want todetermine the volume in a cloud from whence lightningcomes. To have a high probability for photographyof lightning in the field of view the camera shutter mustbe open for the largest fraction of the framing timepossible; the exposure must be short enough thatthe film is not overexposed, and the short duration ex-posure given by lightning must be significant whensuperimposed on the longer duration contribution ofthe background light. These conditions are easy tomeet at night when the background illumination islow. Here it is desirable to have an intervalometerwith a pulse repetition frequency that can be adjustedover several orders of magnitude. In night photog-raphy of lightning it is often desirable to have theexposure sufficiently long that the outlines of the cloudcan be seen by light of the moon or of internal lightning,and it is often desirable that the intervals betweendischarges be compressed. On the other hand, duringvigorous electrical storms the intervals between dis-charges are often less than 4 sec and here one needsfrequent advance of the film to avoid superpositionof many flashes in the same picture.

To meet these conditions for daytime photographyof lightning we place an H-alpha, narrow-band, in-terference filter in front of a long focal length lens inthe manner described by Salanave and Brook.3 Forthis we generally use Linagraph Shellburst film asrecommended by Krider4 in order to obtain the mostfavorable contrast of lightning against the background.With this arrangement we are able to operate with an

open shutter for daytime exposures as long as 15 secwithout fogging the picture background and havephotographed the location of lightning to ground inthis manner. We are now modifying our equipmentfor photographic location of lightning within cloudswith the aid of a whole sky parabolic reflector' and aninterference filter.

Automatic Exposure ControlThe same camera arrangement driven with the nor-

mally open shutter also photographs the cathode raytube indicators in our radars. Here a switch on theantenna drive causes the camera to advance film onceevery antenna revolution at a point of minimum in-terest. For the vertically scanning radar, film advanceoccurs when the antenna is pointing toward nadir,while for the azimuthally scanning radars the film isadvanced when the antenna is directed away from thecloud under study. Use of the Slo Syn drive resultsin a small blank sector on the developed film; this is asmall price to pay for the trouble-free operation ofthese cameras. In contrast, when using solenoiddriven cameras, we often have had to replace fatiguedcamera parts several times each season.

One of the great improvements in exposure of ourdaylight time-lapse films occurred when we connectedthe Slo Syn driven cameras to a photoelectric controlthat varied the duration of each exposure inverselywith the intensity of the incident light. The controlconsists of an intervalometer, a vacuum photocell(Type 934), a capacitor, a latching relay, a voltagecomparator, and various relays and power supplies.The intervalometer provides the basic timing by con-trolling the latching relay in a predetermined cycle.At the start of each cycle the relay is set to open thecamera shutter and also to start the charging of thecapacitor by current flowing from a power supplythrough the vacuum photocell. We arrange the circuitsuch that, when sufficient light has passed through theoptical filter-lens system to produce a proper exposureon the film, sufficient charge has passed through thephotocell and has been collected on the capacitorwhere the resulting voltage is sufficient to trip the volt-age comparator. This in turn causes the reset of thelatching relay which closes the camera shutter anddumps the charge on the capacitor in preparation foranother cycle. If insufficient light is available tocause this action, a followup contact on the inter-valometer resets the latch relay immediately beforeanother cycle commences. For a Bolex H 16 equippedwith the Slo Syn drive the film advance time is about50 msec; the period between intervalometer actionsis about 19 sec. These time values permit a variationin the exposure duration of about 380: 1 which is equiv-alent to about eight stops in light level. Similarly,our Cin E cameras compensate for changes of about40:1 in the incident light level with the photoelectriccontrol. The photocell circuit is adjusted to allow adecrease in exposure of about one stop as the incidentlight level decreases over five stops thus preserving the

1812 APPLIED OPTICS / Vol. 9, No. 8 / August 1970

qualitative impressions of a darkening sky withoutexceeding the film latitude.

An unexpected bonus from the use of this arrange-ment for photography of storm clouds is the high yieldof daytime lightning pictures when the camera is oper-ating under dark thunderclouds even without an inter-ference filter. Under these conditions with low lightintensity the motions of the clouds do not make thefilms unuseable even when the camera shutter is openfor the full 19-sec period. Some of our best views ofcloud-base motions have been obtained with unat-tended cameras under dark storm clouds.

To study the relation between lightning and the in-tense bursts of rain and hail that often fall shortly afternearby lightning, we photograph the whole sky as seenin a convex, first-surface, parabolic mirror using thetechnique described by Von Arx5 with one of the photo-electrically controlled 16-mm cameras. Instrumentsare arranged around the mirror in the field of view ofthe camera to display time, air temperature, electricpotential gradient, point discharge currents, and event-indicating lights controlled by lightning detectors andby rain gauges. While this technique gave us sometantalizing views of the relationships between light-ning and rain with fixed exposure cameras, the greatvariability of light beneath a thundercloud made thepictures that we obtained of limited quality photo-graphically. With the leveling off of the exposurevariations by the photoelectrically controlled camera,the association between lightning and rain is quitestriking as seen in many of our whole-sky storm se-quences.

We are presently working with another camera drivewhich uses a 12-V dc motor and an electrical clutch,again with a cam-switch arrangement. In this drivethe motor runs continuously but the camera movementis isolated from the drive except when the clutch isenergized. Current operating the clutch passesthrough the cam-controlled switches such that thecamera movement can be stopped as desired when theshutter is either open or closed. An external, solid-

state circuit counts down the number of motor rotationsand provides a switch closure at the end of any pre-determined interval when it is desired that the cameradrive advance either a half or a full cycle. This ar-rangement permits photocontrol of the exposure dura-tion from a battery-operated system as well as givingthe advantages of the Slo Syn motor drive withoutrequiring alternating current. The operation of theclutch-controlled camera drive is similar to the coiled-spring drive arrangement developed by Vonnegut2 butdoes not have the power economy and high accelerationsencountered in that system.

The ability to stretch or to compress time by motionpicture photography gives us insight into physicalprocesses. With the rapid advance of technology weare sure that better equipment will become availablefor time-lapse photography, and we look forward to thecontinued development of this technique. If thereare any groups who wish to develop time-lapse cam-eras of their own, we will be glad to aid them as we can.Information on any new techniques that can be usedin our work will be welcomed.

The work described here has been supported by theNational Science Foundation under Grants 11089 and1497, and by the Office of Naval Research. We wishto thank these agencies for the support that made thecameras possible. We also thank the many studentphotographers who have helped us in this work.Among those who made significant contributions areJames Bauer, Benjamin Husted, Donald McCaig, andDavid Rust.

References1. V. J. Schaefer, Appl. Opt. 9, 1817 (1970).2. B. Vonnegut, Appl. Opt. 9, 1814 (1970).3. L. E. Salanave and M. Brook, J. Geophys. Res. 70, 1285

(1965).4. E. P. Krider, J. Geophys. Res. 71, 675 (1966).5. W. S. Von Arx, Weather 13, 179 (1958).

: Moire effect-two radial figures superim-posed; see the book review on page 1963

August 1970 / Vol. 9, No. 8 / APPLIED OPTICS 1813