Methods and Apparatuses for Dividing Photographic Film Longitudinally

[NOTICE]

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this work except in compliance with the License. You may obtain a copy of the License at:

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, this work is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

[Introduction]

Half frame cameras are extremely common and the mechanisms for splitting a frame in half vertically (from the perspective of a typical photographic frame and movement) are trivial. For example almost all motion picture cameras shoot in what the photography world would consider “half frame” if not smaller (super 35, various perf sizes). What is not common is splitting the frame horizontally (from the perspective of a typical photographic frame and movement). This article demonstrates and documents nearly all possible ways for achieving this longitudinal split.

While this article will focus primarily on 35mm stills film as the medium in which this kind of frame splitting is implemented, it is not limited to 35mm stills film but applies to many other film types such as 120 film and motion picture film. There are many differing methods for achieving a longitudinal split. The split does not always have to be 50% of the frame but that will be the focus of this information. First I will cover “movement” methods aka the order in which photos would be shot on a roll of 35mm film.

Some of these apply more to other formats than others. For the most part any time “cassette” is mentioned below this could be substituted for “roll” or some other delivery mechanism. These movements also assume the camera is a typical stills style camera unless otherwise noted, this is because some movements may be simplistic for a stills camera (the first below) but when in something like a motion picture camera they become completely impractical.

[Movement and Switching Methods]

Traditional Movement Sequential Switching

The simplest of movement methods with no complexities needed outside that of a typical stills camera film movement. Each full frame is extracted one at a time from the cassette as usual. One half of the frame is exposed, then another. This continues (top bottom advance) till the end of the roll. The film is then wound back into its cassette and ready for processing. (This applies to 120 style roll film as well but note 120 film does not typically “wind back”.)

This method ensures that frame spacing is accurate but requires the longitudinal split change mechanism to operate for every single shot fired, thus increasing wear. Frame spacing in the context of this article is the alignment of the position of each half of the exposed frame, relative to a typical full frame exposure. Some movement methods require complex solutions to maintain consistency in this spacing for each “half” of the film. Because this method exposes each half before advancing to the next full frame (moving the film), consistency will remain intact.

Traditional Movement Hybrid Switching

While very similar to the Sequential Switch movement, hybrid switching reduces wear on the longitudinal split mechanism by delaying the switch an extra shot. For example; the frame is exposed on the top, advanced to the next frame, then exposed on the top again, but before the next frame advances the switch occurs, now allowing the bottom half of the current frame to be exposed, the frame advances and the next bottom half frame is exposed, the switch occurs again and the cycle repeats. This would be simplified as: top bottom advance bottom top advance...

This movement could require more mechanical complexities to achieve but still will maintain correct frame spacing with much less complexities than some of the movements outlined after this one. It is assumed the first frame of a new roll will switch after the first half is exposed, thus starting a fresh cycle, but this movement does not actually require this and could be omitted to reduce complexity at the cost of a single half exposure wasted. This movement does also apply to 120 or other styles of film.

Inverted Traditional Movement and Hybrid or Sequential Switching

There are many cameras that use inverted traditional movement IE: the film is first extracted from the cassette and then wound back into it as the film is exposed. This movement would use Hybrid or Sequential switching, with hybrid being more favorable due to less wear. This movement maintains accurate frame spacing while also maximizing film economy. Complexity is slightly more than normal traditional movements but not by a significant amount. This Movement also protects film from accidental exposure if the back were to be opened before the “end” of the roll. A camera using this method is also uniquely able to "pre measure" the total length of the film to get an accurate total exposure count.

Hybrid Traditional Movement Linear Switching

This method employs a typical film movement with some significant differences. The longitudinal split change mechanism only operates once per roll. For example frames are extracted from the cassette and only the top half of the frame is exposed. At the end of the roll the half is switched, now exposing the bottom of the frame as the film is shot and wound back into the cassette, akin to inverted movement. This movement can reduce wear and complexities in the split change mechanisms, but comes at the cost of increasing complexities in frame spacing alignment mechanisms and film movement.

A camera utilizing this movement would have to be able to extract frames forward and backwards the same repeatable distance. It would also need a system to “know” when the end of the roll is reached but an entire frame hasn’t been fully extracted. This can be achieved via DX code frame counts, optical or mechanical measurement of the film length, clutch systems, etc… but must be complex enough to ensure frame alignment consistency. The logical evolution to this is complex movement.

Complex Movement and Switching

Movement of the film is handled by complex systems which have full control and monitoring of the film’s position allowing for accurate frame spacing using any switching method. This would likely be implemented using a pre tension system so film slack within the cassette is not an issue. More complex motions and methods of switching can be achieved with complex movement control. Many of which are not recommended but some do provide the shooter more creative freedom.

One example is the following: A camera which allows half frame and full frame photos to be captured. Cameras like this such as the Konica Autorex already exist for traditional vertically split half frame. Complex control would allow a system to intelligently be aware of which frames have been exposed and where.

This could allow for more creative freedom by the user, granting them the ability to shoot an entire frame, a sequential top then bottom shot, or linearly shooting just one half as they desire, all while being able to switch between any format or switching style at their will. The camera would keep track of what frames can be shot in what ways, and have the ability to skip over already fully exposed frames.

Of course this example is taking the capabilities to the extreme. Most cameras with complex movements and switching will simply provide traditional movements with more accuracy. Complex movements will be more difficult to implement in general, but may actually end up being less mechanically complex since electronic systems will most likely be used to manage frame advance and winding operations. Complex movements can also have control over frame border size, not necessarily being limited to sprocket hole spacing for each frame, thus granting maximum film economy.

Other Movement and Switching Styles

There are a plethora of other combinations of movements and switching styles but most come with no real benefit. For example: simultaneous capture is one that defeats the point of a half frame format except for 3D imaging. One not-so recommended but useful and easy to implement movement is traditional movement with manual (linear) switching. This is the method I use for achieving the Ultra Half Frame format in almost any camera.

The film is shot entirely on one half, wound back, then shot on the other half and wound back again. For a dedicated camera this may be trivial to implement, including a method for achieving accurate frame spacing, (a simple film clamp on the main take-up spool and a repeatable winding system), but the excess extraction cycles on the film can cause longitudinal scratches on the film emulsion due to contact with the film cassette and camera.

This should be avoided unless necessary, however in a camera system that does not utilize a film cassette such as a motion picture camera, this may be one of the best and only practical ways of achieving the split. Double 8 motion picture film is an existing format which utilizes a forward then reverse movement for longitudinal splitting in motion picture cameras by flipping the film after one half is shot.

[Splitting Methods]

Moving on to the actual methods for splitting the film longitudinally. Again the focus here is on the 50% split aka Ultra Half Frame using 35mm film, however many of these methods could be used with other film sizes to achieve different results. These methods are for the most part agnostic to the movement and switching style, but some will work better with certain movements than others.

Single Lens and shutter with frame block

This is the simplest of all methods and will provide a basis for explaining definitions and problems that will come up in methods that follow. Single lens means there is only one taking lens, it can be removable, fixed, single element, etc, the point being there is only one, just like any regular camera. All other methods assume single lens unless otherwise specified.

A frame block is simply some kind of object that blocks a part of the frame from being exposed. Frame blocks should be placed as close to the film as possible to ensure a sharp image separation. The farther away a frame block is from the film the more light will pass beyond the edge of the frame block, possibly causing exposure on the other half of the film. When I came up with the idea for Ultra Half Frame I used a piece of tape on one half of the film gate behind the shutter and in front of the film, only allowing me to expose half of it at a time, this would be a frame block method.

To further expand on what a frame block is: it can be fixed or moving and mechanically controlled, electronically controlled, etc. For example: tape is a fixed frame block that a user must remove or move themselves in order to switch framing. Inversely a camera could be made with a small toggle that moves a piece of material up or down allowing you to select either the top half, the bottom, or even no frame block at all, this would be a moving frame block. This can be further expanded with automatic systems that move the frame block without user intervention based on camera states.

A frame block based camera could be designed to be extremely flexible. A camera could shoot multiple different formats by simply using different sets of frame blocks. For example Full Frame, Half Frame, Ultra Half Frame, Quad Frame, 1/3rd Frame, etc… Even complex shapes and masks can be achieved with frame blocks. Different sets of frame blocks will of course create more complexities in the movement and switching styles that may not be fully explored in the above section (for example: UHF to Quad Frame to HF to Full).

Despite its simple implementation, there are a number of problems with this method. One of which is the lack of optical centering ie: using the center part of the lens instead of just a portion of it. This means you will always be using only one extreme of your lens, the top or bottom. I got around this when shooting the 2nd roll of Ultra Half Frame by using a shift lens. This problem could be remedied with a shift lens (or some type of optical system) linked to the frame block. Focusing may also become an issue depending on the system used to achieve focus.

Another problem with this method is composing a shot. A second system will be required in the viewfinder or some method of letting the shooter know what half of the frame they are capturing. This could be very rudimentary such as a top half indicator with a typical SLR setup, or a complex system that automatically limits the shooter’s view.

This can be achieved by physically blocking the viewfinder’s optical path, possibly linking a viewfinder block to the frame block, or electronically by cropping the shooter’s viewfinder in some way (LCD overlay or EVF cropping for a digitally assisted system). A vertically traveling half sized SLR mirror would require far more complexity to correctly implement in a single lens frame block system than other more appropriate methods for SLR style cameras.

Multiple or Complex Shutter

Similar to frame blocks, multiple independent shutters could be used to control frame exposure. Each shutter would be its own mechanism and can fire independently. This of course adds more mechanical complexities than simply using a single shutter and a frame block. A complex shutter could also be used, this is a single shutter which can be set to only open for a portion of the frame, allowing the shutter itself to control where on the frame the image is exposed. A complex shutter would be ideal for flange distance space saving since no other mechanisms such as frame blocks need to be placed between the film and lens. This method has the same usability downsides of the previous method.

Multiple Lenses and Shutters

This method is slightly more complex than frame blocking but the easiest of all methods to implement on a basic level. Each half of the frame has its own shutter and lens. This is the only method to split the frame longitudinally that exists at the time of writing in a commercial camera (that I’m aware of) besides double 8 motion picture cameras.

Many cameras use this self explanatory method, most notably the Nickelodeon PhotoBlaster and Lomography Supersampler both of which are half-half (quad) frame cameras (H2 – 4 shots per frame), these use traditional movement and sequential switching. There is also the Fujifilm Byu-N 16, a dual half-half-half frame camera (H3- 8 shots per frame but 2 frames at once so 16 lenses and shutter mechanisms).

This method still suffers from the composition problem previously explained. Most of the commercial cameras using this method simply employ fixed focus lenses and a fixed viewfinder with no indication as to what you are really shooting. A multi lens system does not suffer from optical centering issues, but in general this method is not recommended due to the added cost of having multiple independent optical paths.

While not necessarily complex on a basic level, this method would be significantly more complex if one were to expect advanced features such as TTL focusing/metering, auto focus, etc… as compared to other single lens methods simply due to the nature of having more than one taking lens.

Multiple Optical Paths

Possibly the most impractical method, the image from a single lens could be redirected to different portions of the frame using an optical system within the camera. The optical system would likely be composed of a set of moving mirrors. Image centering would not be an issue but ensuring the length of each path is equal may be challenging. Keeping the optical path clean and maintaining the moving parts would also be a problem. A lot more flange distance would be required for this method. Implementing an slr style viewfinder with this method may be easier since the optical path is already being redirected within the camera.

Moving Optical Path

This method moves the entire optical path, including the lens or lens mount to facilitate the longitudinal split. This movement can include the shutter but is not required to fit this definition. The film gate must either move with the lens or the camera must utilize frame blocks to restrict exposure on the other portion of the film. This method and the following give the best results but are the most complex to implement.

A camera (Blaž Semprimožnik’s OKTO35 Mk3) does currency exist which uses this method to longitudinally split the frame, it is sadly only a prototype and not a commercial product. The OKTO35 Mk3 splits the film into 4 logitudinal sections or “tracks” using a moving optical path.

With a moving optical path you still will struggle with framing, unless your viewfinding system is also attached to the moving optical path, like in an slr style system. I feel this is the second best option for splitting the frame logitudinaly, and possibly the best depending on the application. Shift lenses intigrated interally or externally, when linked with a gate or frame block are a form of moving optical path.

Film Plane Movement

The entire film transport is made to move up and down to facilitate the longitudinal split in the frame. This means you only need one lens, a fixed gate, and a single shutter. The vertical movement of the transport can be electronically or mechanically controlled. It does not have to be automatically driven by any mechanism but could be operated by the shooter. 35mm film only needs approximately 12mm of vertical travel to facilitate a single longitudinal split. The mechanisms which move the transport could be made very simple or very complex.

Moving the entire film plane is the ideal solution to splitting the frame. With this method you can use a fixed viewfinder, or implement an slr style system just as you would on a regular camera. No special mechanisms are needed to achieve focusing or framing outside of the typical ones that all cameras already use.

An interesting side effect of this method if the transport were to be fully electronically controlled with complex movment, one could also implement a quasi “IBIS” system to reduce camera movement during exposure. Because this method is most likely to be combined with a complex movement, linear switching is recommended to reduce wear.

This method may seem similar to the previous moving optical path (lens) method since depending on how you look at things, who is to say what part of the camera is actually moving and which is static. To specifically define this I would consider film plane movement to take place within the camera operating on the film in some way, where as optical path movement would require some part of the camera externally (like the lens) or an internal optical system to physically move.

For example, the double 8 motion picture film format uses film plane moment since the reel is flipped upside down, thus moving the film plane to allow exposure on the other half of the film without moving the optical path. Double 8 may have been the first ever longitudinally split format, released in 1932.

Etc...

There are of course a plethora of other methods, mostly consisting of mixtures of methods already outlined above ex: multi lens single shutter with frame blocks, moving optical path with fixed gate and frame blocks, etc… These need no explanation and most are overly complex for no benefit. I believe the only three viable options for creating a versatile modern camera are: Film Plane Movement, Moving Optical Path, and Frame Blocks.

[Conclusion]

Ideally a film camera could be made using a modern lens mount. In fact even an SLR could be designed to fit inside of a modern mirrorless mount such as L mount because the mirror can be much smaller, thus not requiring as much space behind the mount and in front of the film, shutter, and gate.

Yes an Ultra Half Frame SLR camera IS possible with the approx 15mm of space behind the mount, though it would be a significant design challenge requiring some unique ways of moving the reflex mirror. This fictional camera is the basis for many concepts I have for future designs and ideas for the next generation of film cameras, some of which I will cover in more detail in future articles.

I have chosen to license this page and its accompanying articles under Apache 2.0, including its patent grant provisions to allow individuals and companies to create and sell products based on this information, for free, while also not allowing them to stop others from doing so. IE: I want as many people to use these concepts as much as possible. I myself would like to manufacture and sell cameras based on these designs so if you are interested in making that happen, please contact me.