Bracket for Strip Photography

36O degree wide angle and racetrack photofinish photographs
made easy with this motorized rewinding attachment

Andrew Davidhazy
Imaging and Photographic Technology Department
School of Photographic Arts and Sciences
Rochester Institute of Technology

A large number of camera systems and photographic techniques are based on scanning principles. Two applications that come readily to mind are racetrack photofinish cameras and extreme wide angle "Cirkut" type panoramic cameras.

The common features in these cameras is that the film within them moves during exposure and that the cameras have no conventional shutter but expose the film for a short period of time passing it under a narrow slit located usually between the lens and the film. As the film passes under this slit it is exposed to light. If this light is an image of an object, and this image moves at the same speed as the film, then in relation to it, the film is exposed to a basically stationary image during the time that the image and film travel across the width of the slit

Since in these "strip" cameras the image must move at a particular speed in order to be properly recorded, if the camera is stationary the object must move. On the other hand, if the subject is stationary, the camera must be moved to establish the condition of a moving image at the film plane. The first arrangement is the one on which photofinish cameras operate and the second is the one by which true panoramic cameras operate.

While cameras like these are commercially available, I have found it interesting to explore the "basics" by adapting my regular 35mm cameras to experience, with somewhat less than technical perfection, the unusual imagery which these camera systems can deliver. At the heart of these experiments there are two items which one must install in or on the camera. One is a narrow slit and the other is some means for transporting the film through the camera.

The first is easily accomplished by simply installing a slit in the camera's focal plane, just between the film plane rails located on either side of the image gate inside the camera, as shown in figure 1. As you can see, I prefer to use thin, black, opaque paper, plastic or thin litho film which has been processed to maximum density. This slit material or the tape with which it is held in place must never lie over the film plane guide rails because this will prevent the film from moving freely within the camera body.

An alternative location for the slit is in front of the camera lens. It can be easily made by masking down a rigid lens shade with some opaque material, leaving a 1 mm or 2 mm slit running from the top to the bottom edge and centered sideways on the shade. Cokin Corporation sells a mask intended for just this purpose to fit their filter system. This is the safest but not the most efficient location for the slit since it tends to interfere with the lens's optical properties.

Next, while in commercial equipment great pains are taken to make the film moves at a steady pace by driving it between pinch rollers, my experiments have been successfully carried out by assuming that the motion which the film has during the rewinding process is even enough for many purposes. Therefore, I have recommended that one simulate the operation of a strip camera by manually rewinding the film with the camera's shutter locked in the open position.

For some applications, especially panoramic strip photography, manual rewinding is not possible because the camera must rotate as the film is being rewound. This would call for an unusual amount of manual and mental dexterity and concentration. To remedy this shortcoming I have devised a motorized rewinding bracket which can be fitted with minor alteration to most standard, manual, 35 mm cameras.

[strip bracket device] Basically, the bracket's purpose is to hold the camera and a DC gear head motor in such a relationship that the turning shaft of the motor will engage and turn the rewind lever of the camera. By varying the voltage to the motor a range of film speeds can be chosen to meet the needs of a particular application.

As you can see from the illustrations, the camera is attached to the long leg of an "L" bracket while a movable extension, which holds the motor, is attached to the short leg of the bracket. The height of this short leg above the base should be adequate to provide space for the motor shaft to end up just above the rewind knob of the camera. The dimensions given, if used with the recommended motor, should fit many cameras. Small height adjustments can be made by lowering the motor through the clamp which holds it. Side-to-side adjustments, needed to center the motor shaft over the rewind shaft are made by loosening the tension on the bolt holding the motor clamp to the "L" bracket, placing the motor in the right position and then retightening the wing nut on the connecting bolt.

The wood used can be any clear 3/4" pine or plywood. All parts can be cut from a 2 1/2" wide board and their shape and number are illustrated in Figure 2. You will need one long piece for the bottom which should be about 9" long, two 4 3/4" pieces to make the riser to which the motor clamp will be attached, a 2 1/2" piece to serve as top, and a 6" length from which the motor clamp will be fashioned. Along with the wooden parts you'll need a 2" and two 3 1/4"x20 stove bolt with washers and wing nuts, one or two similarly threaded "T" nuts, a 3/4" long by 1/4 x 20 bolt, parts to fashion a crank with, and a 12 or 24 volt DC gear head motor with a top speed of about 30 or so RPM depending on your application.

Gear head motors like this are sold by a variety of sources. Two companies that I know of are: AST Servo Systems, 115 Main Road, Montville, NJ 07045 whose stock numbers DM-404 @ $ 12.50 and DM-495 @ $ 21.50 are applicable. Also, Herbach & Rademan, of 401 E. Erie Avenue, Philadelphia, PA 19134 whose motors numbered TM23K021 @ $ 12.50 and TMK24K57 @ $ 19.50 also are possible choices.

After you have all the pre-cut pieces of wood ready you will drill the holes and slots by which the camera and motor will be attached to the bottom and top pieces respectively. Once this is done it will be simply a matter of assembling the bracket, attaching the camera to the bottom piece and installing the motor in its moveable clamp so its drive shaft ends up just above the camera's rewind knob.

So, to start, along a line about 2 1/2" from a short edge of the long piece drill two holes. The first should be a 5/16" hole about 1/2 inch from the edge and the other, a 1/4" one, at about 1 1/2" measured along the same line. With an oversized 1 1/2" wood bit, drill partial holes (essentially countersinks) which extend about 1/2 way into the wood where these holes have been drilled. These should be drilled from opposite sides of the bottom piece since one will be used to insert a 1/4x20 "T" nut into it while the one on the bottom side accomodates a short 1/4x20 bolt to fasten the camera to the bottom support. Actually you may want to drill the countersinks first and then expand the center holes to 5/16" and 1/4" respectively.

[strip bracket device] You may also wish to drill an oversized hole which will go all the way through the bottom piece at a position which is just below the rewind button of your camera. You will need access to this area in order to disengage the camera's sprocket for rewinding. Since the exact location of the rewind release button varies widely among camera brands you will have to determine it's location for your particular situation. Refer to the construction photos for visual detail.

[strip bracket device] In the top, 6" piece, you will have to drill, and cut, a slot with a coping saw within which a 1/4" bolt can slide and cut a circular hole near the other end which has a diameter equal to diameter of the motor body. See Figure 6. Typically this is roughly a 1 1/4 or 1 3/16 ths inch size hole. It should be far enough away from the edge that you can drill one long 1/4" hole through the width of the top piece within which one of the 3" long bolts will be used to tighten the clamp's grip on the motor body.

Cut out a section near the thin end of the motor body hole so that the pressure which will be exerted on either side by the tightening clamp will, in fact, hold the motor body tightly after the motor's position within the clamp has been chosen. Drill another 1/4" hole all the way through the other end of the 6" piece and push the other 3" bolt through it. Its purpose is to provide some strength and integrity to the top piece to prevent it from breaking (or to simply hold the piece together!) if the other end is clamped too tightly causing the top piece to break.

You will finally have to drill a 1/4" hole through the center of the small, top, cover, section.

At this time you should insert the "T" nut into the 5/16 " hole in the long, base, portion of the bracket and then you are ready to start to assemble the parts. You can use nails, or screws, and wood glue for assembly. Attach the 4 3/4" pieces to the upper side of that end of the 9" piece which is away from the camera and tripod fastening hole as shown in the illustrations.

After inserting the 1/4x2Ox2" stove bolt through the center hole of the top piece, fasten it to the two risers so the bolt sticks upwards and let the glue dry thoroughly. Your bracket should look as shown in the illustration.

Insert the motor body thorough the hole prepared for it in the movable, top section. You may have to enlarge the spacer gap slightly to allow the motor body wires to slide up so that the motor is held by the clamp properly. Push the 1/4x2x3" stove bolt through its hole and attach a wing nut to the protruding end.

When all is dry, the slot in the top, motor clamp, piece should fit over the bolt protruding upward from the bracket's top piece. Attach the second wing nut on the end of this bolt. Tightening this nut should provide a firm connection between the clamp and bracket sections.

[strip bracket device] You will need to fashion some kind of a lever which will fit onto the shaft of the motor. There are many ways of doing this but the one I used was to buy a hexagonal spacer with a hole equal to the motor shaft diameter and drilling and tapping two holes into it. One of the taps was to provide for a set screw and the other for a small bolt which was long enough to reach the drive knob on my camera's rewind lever with the motor shaft centered over the rewind shaft. This is shown in a detail illustration. I have also used the throttle control lever used on model airplane engines to fashion an appropriate lever.

Using the 1/4x20x3/4" round head bolt, attach the camera to the bracket. Adjust the position of the camera and the position and height of the motor shaft so that they line up reasonably well and tighten the wing nuts.

You need to attach appropriate battery connectors or terminals to the input leads of the motor. Identify the leads properly so that the motor will cause the rewind knob to turn in the correct direction. The finished bracket, with camera attached, should look as shown.

To use this strip motor attachment, you will need to adjust the time that the motor takes to turn the rewind knob by adjusting the voltage to the motor. This can be done by simply changing the number of batteries that power the motor and/or including some means for providing variable voltage to the motor. The suggested motors can be driven with a 9v "transistor" battery, but since they draw so much power, each battery may only last for one or two rolls of film. Use larger capacity batteries, such as motorcycle batteries, and hook them up in series to get higher voltages. The suggested motors will run fairly well at voltages from about 3 to 24 volts. To get higher or lower speeds you will need to research the availability of motors which have the speed required for your particular application. The motors suggested can be used for many low speed applications.

If used indoors I suggest you invest in a relatively low cost multi-voltage "battery eliminator" that provides from 3 to 12v DC in increments of 1.5 volts. This will drive your motor at variable speeds without having to use up batteries.

The procedure to use to make strip photographs is to disconnect the motor's lever from the rewind knob, load the camera with film, and then advance it all to the take-up side with the lens cap on. At this time or earlier you should select a suitable subject and make appropriate calculations for the rate at which the rewind lever must turn, etc. as explained later. Next, reconnect the motor lever to the camera's rewind lever, then set the shutter on "B", lock it open with a locking cable release, depress the rewind release button and while making sure it stays depressed, activate the DC gearhead motor which now rewinds the film

Note that some cameras do not allow this and others drain their batteries rapidly when an extended time exposure is made.

As the film passes the slit which you have installed in the camera it gets exposed making a more or less accurate record of the images that also travel by the slit. The more accurately the speed of the moving images matches the speed of the film the more accurate the reproductions will be.

To use this "strip" attachment to make wide angle photographs you will need to rotate the camera while the film is being rewound. The camera can be panned by hand or by placing it on a motorized panning head such as sold by Cambridge Camera and others. If you pan by hand there may be some changes in speed but this method, of course, lends itself to creative experimentation. Once you have set a particular panning speed stick to it. Then, looking through the viewfinder notice the length of time it takes a particular area of the subject to go across the viewfinder. At this point adjust the voltage to the motor in such a manner that the rewind shaft of the camera turns once in 1.5X the time it takes the subject to cross the viewfinder.

Alternately, if you can not readily change the rewind speed, place a zoom lens on the camera and adjust the lens focal length to that setting at which any given stationary subject crosses from on side of the viewfinder to the other in 2/3 the time it takes the rewind knob to turn once. Wide angle panoramas as wide as 360 degrees are possible by this method!

If you are using the camera as a photofinish type camera, then simply fix it on a tripod and aim it at the area of interest. Watch and time the length of time it takes your subjects to go across the viewfinder and adjust the motor speed according to the procedure described above. If you can not adjust the film speed to an appropriate value, use a zoom lens and alter subject size in your viewfinder until hopefully the subjects cross the viewfinder at a speed which is within the range of your motor.

That is, the subject should travel across your viewfinder in 2/3 the time it takes the rewind knob to turn once. You will find that as the image size is made smaller by using successively shorter focal lengths, the speed of the subjects across the viewfinder will become less in direct proportion to the lens focal length.

Assuming that the width of the slit which you placed within your camera is 1 mm, then it is easy to determine the exposure time at a given rotation rate of your rewind knob. Basically, the faster the knob turns the less the exposure time. The actual exposure time which will result from a given rewind knob rotation rate is found by dividing the time it takes the rewind shaft to turn once by 50. Thus, if it takes 2 seconds to turn once the exposure time is 2/50 or 1/25 second. Make a meter reading for this exposure time and adjust the f/number on the lens to give you a properly exposed negative at the exposure time which you determined previously

While there are a number of commercially available panoramic cameras such as the Globuscope, the Hulcherama, the Alpa Rotocamera, and others, racetrack strip cameras are generally only available from specialized manufacturers such as Specialty Instruments Corp. Under certain conditions panoramic cameras can be operated as improvised racetrack cameras by holding them by their bodies and allowing the motorized bases to turn freely. Racetrack "strip" cameras, however, are not easily adaptable to panoramic work. There is one Japanese company which builds and sells a commercial version of the home made motorized bracket. described above. It is the Sugawara company and the product is the Sugawara Film Streak V.

If you have questions or want to discuss any aspect of scanning photography feel free to write to me right HERE or later at