The Pyrotechnics of Slit-Shutter Films

by Jno Cook

Some say that these are not films at all, for they have no location in time, and also because they can be projected forwards or backwards, and can be shown at speeds which have no relationship whatsoever either to reality or to the taking speed. They are, it is claimed, about space, not about time, and therefore do not adhere to Frampton's model which holds film as a metaphor for linear thought, presumably developmentally based in time. Also objectionable is that these so-called "films" are projected sideways - never mind that Edison's and Muybridge's original ideas were to do the same. I might add to this the objections that slit-shutter "films" also have no frame lines, being composed end to end of a single frame, or, at best, of separate camera takes terminated with a flash of light or a fade.

Yet these type of films are being made on film stock, processed and printed by film labs, and projected to audiences riveted to their seats in darkened auditoriums in the manner traditional of the "normal" films composed of flickering discreet images. What are we to make of the efforts of the few who are recklessly proceeding with this type of imagery in total disregard of traditions, and are insisting on calling their efforts "filmmaking?"

Let me first establish something of the tradition within which this work is being done, for in effect slit-shutter images are nothing new. After this introduction I will detail the technical aspects of camera construction, in the hope that if enough people take up this medium, some of the reluctance of tradition will be overcome.

Tradition

We could point first to Adrian's column in Rome as a precursor from antiquity, or the tapestry of Bayeux, but all of filmmakerdom could hold the same as their long lost grandfathers, especially as these are both discreet panels of images - frames, if you like. Perhaps closer to an exclusive tradition, which does not otherwise intersect with filmmaking, are the panoramic daguerreotypes made in France in the 1840s, which depended on the simple optical fact that rotation about a vertical axis of a lens does not relocate the image made at the focal plane. These cameras used rotating lens mounts, flexible bellows, curved plates, and a slit-shutter located near the focal plane. Similar claims can be made for the real or imagined dioramas made in the 19th century, daguerreotypes from New York to St Louis, and after 1865 of the continued trek to the West coast, all the discrete images strung together as prints or repainted on rolls of canvas and used as carnival attractions, each unrolling presenting a thousand miles or more - or so it has been claimed - all lost of course.

By the early part of this century the slit-shutter camera has evolved into the well-known banquet camera, many of which are still in use today, and of a design still made today but now in miniature formats. By the late twenties this type of camera is also used to record the finish line at race tracks. Here the obvious has happened: the availability of long rolls of film has allowed the rotating lens to be dispensed with. The pseudo-rotation, instead, of the field and the movement of the film are used instead to record sensible images of the moving horses, although with an unchanging background.

Other more contemporary and industrial uses can be found: in Japan the slit- shutter camera is used to record road surfaces for maintenance. At the National Geographic it is frequently used to depict on a two dimensional plane the cylindrical surfaces of vases. I might add that the Xerox machine is a slit- shutter camera, where the copy bed and drum rotate or slide past each other.

Recent Filmmaking

A number of people are using 35mm slit-shutter cameras in film making in Chicago. Peter Thompson has used a slit-shutter camera in filming trajectories through the Mayan skies in the Yucatan peninsula for incorporation into a film on a Mayan shaman. This involved not only the normal rotational sweep of the camera, but a circuit which alternately pointed the camera to the ground and the sky. Viewing needed some means of righting the image as it descended from the sky. His projection equipment thus rotates the image, that is, turned it upside down, after each sky circuit, and right side up again as it passed along the ground. Naturally, the projection equipment is only designed to transfer the images to standard film stock or video.

Kosta Dimitreas started using a 35 mm slit-shutter hand-held, and has recently started experimenting with the inclusion of moving persons within the scope of the scan, which results in body parts seeming to hang in the air as the subject withdraws from the sight of the scan. The purpose of film-making here is both for the production of exceedingly long panoramic images and to produce projectable film stock.

Gabor Csaszari, a Hungarian film maker, a few years ago started to develop a narrative series by moving persons past the slit of a stationary slit-shutter camera, using a finish-line camera borrowed from the Omega Company of Switzerland, which initially used unperforated 35mm stock. After changing to perforated 35mm film the images could be viewed with more readily available modified 35mm projection equipment. Currently a modified flatbed editor is used for projection, equipment which allows projecting two films simultaneously. Films have been shown in Glasgow, Paris, Hamburg, and Budapest.

The author, Jno Cook, has worked with Csaszari and independently to produce slit- shutter films. Cook has also been a major supplier of 35 mm cameras and projection equipment in Chicago. Recently exhibited was a record of the ever-late starting of the annual Flotilla floating art event, during which the camera accidentally turned over into the Chicago river and kept rotating under water. Modified projection equipment exhibited the half hour river-dunked "Waiting for Flotilla" as a four hour film.

Advantages

What are the advantages of slit-shutter camera in cinematography? Foremost is cost savings. Fifty feet of 35mm cine film can be used to record for a half hour or an hour and a half, and can be used to project images for an equal time or for a period ten times as long. This is of course because the camera records only a differential image, like a xerox machine or a fax machine, but a large section of the time-adjacent integrated image can be projected at the same time.

A second advantage is the welcome change in metaphor. The slit-shutter film is definitely about space, not about time. This requires a way of thinking which connects elements throughout a field of adjacent objects rather than the more familiar method of thinking in scripts. Some visual artists will welcome this, for it might break the insistent application of narrative as the imposed model used by viewers to order the sequence of film images. Many viewers will reject this, however, for slit-shutter films are still experienced in time when presented, and the first means most of us will use to make sense out of the imagery is to attempt a script construct - to superimpose a story onto the sliding image as it unrolls before us. There is much room for aesthetic investigation here.

There are disadvantages also. What stands out is the fact that nothing much really happens (a time-based notion) in slit-shutter cinema, and thus the motion of motion picture realism is simply negated. If expectations are formed from a life-time of seeing traditional films, disappointment will ensue quickly. This shortcoming follows from the fact that the film is recorded incrementally, but the constructed image is whole, and projection of the image is not related to the recording methods, for a section of the whole film is simply projected as if it were a moving slide - in effect a film strip. More experimentation with the as yet undiscovered diversity of recording and projection methods and with an extensions of the basic principals will surely bring improvements in the future. So will an extension of use of this equipment by more filmmakers.

Optics and Operation

The operation of a slit-shutter camera is based on the principle that the image formed by a lens does not change or move in space if the lens is rotated about an axis which is perpendicular to the axis of the lens and goes through the rear nodal point of the lens. In other words, it is possible to rotate a slit-shutter camera about itself and record a sensible image of the surroundings. Rotation does not need to be limited to a single 360 degree rotation, it can be any number of turns. In practice it matters little if rotation is about the "rear nodal point" of the lens or some other point. Distortion does not show up except when using very wide angle lenses. Translation can be added, so that the camera may move along a straight line path as it rotates. Slit-shutter films have been recorded from moving vehicles along highways. If the translation is not too fast, or if the subject matter is far from the camera, the image will still be mostly sensible.

Building a Camera

Now, how to build a slit-shutter camera: All one needs for a start is a camera which will advance film continuously past the film plane. I have seen Gaylord Herron, a photographer living in Tulsa, use a broken 2 1/4 twin-lens reflex camera with a cardboard shutter at the film plane. He held the camera sideways, and hand cranked the film while he rotated about his position. Somewhat choppy results, and only viewable as photographic prints, but it illustrates the principles involved.

It would be better, for those of us who want verisimilitude and tripod-steady images, to use an electric motor somehow attached to the film take-up or to a sprocket-drive film advance. A second motor would be used to rotate the camera. Generally slow motors are needed, like a gear motor. This is one which could operate in the range of 6 RPM to 1/100 RPM. If an AC motor is used, the speed will be guaranteed to be steady, but not adjustable. If a DC motor is used the speed can be adjusted over a wide range by changing the voltage at which it operates, and can be controlled with a voltage regulator. DC motors make for more portable cameras.

One need not worry about the speed of the film advance at first. The film advance speed will determine how fast the camera needs to be rotated (the second motor), and will determine the shutter speed. More about that below. The question which needs to be answered at this point is, How long is the image of a single rotation of the camera? The answer is that for a correct ratio of height to width, you will need to move an amount of film equal to 2 times pi (3.14) times the focal length of the lens.

image length = 2 x pi x (Focal Length)

Thus, for a 50 mm lens the film which is transported in one rotation will equal 2 x 3.14 x 50 = 314 mm. If approximately this amount of film is moved past the slit in one rotation, the proportions of the subject will look about correct. Being off by 10 or 20 percent mostly doesn't matter.

The slit size determines the equivalent shutter speed. Obviously it is related to the time it takes to rotate the camera. It is the fraction of the rotation time, that is, the slit-size times the rotation time divided by the image length for a single rotation.

shutter speed = (slit size)x(rotation time)/(image length)

About lenses: Any lens can be used which is more or less appropriate for the film gage. In fact, the lens does not need to cover from corner to corner, only from top to bottom. Thus very wide angle lenses can be used. A long lens will produce a long image (long before it repeats itself); short lenses will make short images. What needs to be done is to adjust the film advance and the rotation of the camera to make the two match.

The gauge of the film doesn't matter much either. The gauge of the film will be determined by the processing methods which are available and projection equipment which can be altered or constructed. Thirty-five mm film stock has the advantage that there is a surplus of film, reliable lab processing, and numerous camera bodies and projection equipment which can be altered. I built my first camera from a 100-foot load Graphlex ID camera, mounted on a rotating base which in an earlier life had suspended a mirrored ball from some ballroom ceiling. I used a 2" enlarging lens found on the streets of New York. The slit was carved into a piece of brass shim-stock with a razor blade; the equivalent exposure was calculated after the fact. I also used all AC motors at first, a mistake, for an DC-AC invertor had to be build before the camera could be taken into the field.

Here is a more recent example, and although it involves a large panoramic camera, it will illustrate the calculations. I wanted to convert an aerial camera which uses 7 inch wide roll film into a panoramic slit-shutter camera which would rotate 2 or 3 times before running out of film. The original camera used a 15" lens. This would have made a 94" image with each rotation. I wanted a shorter image, and mounted a 6" lens. The amount of film which would now move past the film plane is 2 times 3.14 times 6 inches, which is 38 inches. I attached a small 12 volt DC gearmotor to the take-up knob with a drive belt. It moved 38 inches of film in about 45 seconds. The next problem was to find another motor which would take the camera through a complete rotation in the same time. Both motors would operate from a 12 volt lantern battery strapped to the top of the camera. I should point out here that there is one limitation to camera rotation: the motor which rotates the camera should move the camera in the same direction as the film, or no sensible image will be made.

The camera was fastened to a lazy susan, which had a gear mounted to the bottom plate, and was driven with a chain from a motor attached near the bottom of the camera. Once two motors were found which would approximately do the job, one needed to be slowed down. This was accomplished by wiring the second motor through a voltage regulator (plus a heat sink, a resistor, and a 5K variable resistor - all of which can be obtained from Radio Shack).

For the slit I worked backwards to settle on 0.035 inches. This can be measured with a feeler gage such as is used for adjusting points on a car distributor. Go to Giant Auto and get one. The equivalent shutter speed here is 0.035 x 45 / 38 = 0.041 seconds. This will turn out to be 1/24th second if punched into the "inverse" function of a calculator.

16 mm Slit-Shutter Camera

I have never converted 16mm equipment for slit-shutter camera use, but here are some thoughts anyway: Starting with a 16mm B&H Filmo camera it will be observed that this camera runs about 20 or 30 seconds for every windup of the spring. If the spring is held while the camera operates, it will rotate (at 8 frames per second) once every 10 second. Thus the film moved per rotation is 80 frames or two feet of film. Dividing by 2 times pi results in a focal length of close to 4 inches for the lens. This focal length is much too long for hand-held use, and too long for any sort of panoramic image. It might be alright for depicting the endless Illinois prairy skyline, however. Another solution would be to decompress the image with the use of an anamorphic projection lens.

To complete the conversion of the camera, the claws and shutter would have to be removed. Two rollers would have to be added to allow the film to smoothly pass by the focal plane. A slit-shutter would have to be added between the lens and the film. To achieve 1/24th second would require a slit of 0.10" for the purpose of this example.

I would prefer to strip all of the mechanism from the Filmo and start over from scratch, designing around the standard 1 inch focal length lens. This would require moving 6.28 inches of film per revolution. Designing the camera to rotate in perhaps 30 second, this would mean that 100 feet of film would last over 3 hours. I can imagine it on the roof of my car as I cruise down some Illinois highway. I would call it a road trip film. Projected sideways with altered 16 mm equipment, the film could easily stretch to six hours. It would be an epic film.

Jno Cook is an aesthetic investigator.

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