“Slit-scan”, “Photo-finish” or “linear strip” photography is a technique where an image is created while the film moves past a narrow slit. Most people are familiar with the “photo-finish” used in for example the Olympics or horse racing. A slit-scan image is made up of many narrow slices of time assembled side by side. The image is not of an instant in time as per conventional photography, but rather a measure of time stretched along the length of the film where events having occurred in the same position over a given period of time are represented.
Since 2008 I have been developing a slit-scan system based on a Pentax ME Super SLR.
Some examples shot with my custom Slit-scan camera:
So, how does it work and how is it different to the standard unmodified SLR?
There is a slit instead of a shutter The shutter curtains have been recycled into a precision 0.5mm slit installed at the film gate of the camera. The slit is positioned centrally so that the centre of the split prism on the focusing screen corresponds with the slit position. The shutter release button on the camera has no purpose, the self timer has also been removed. If the lens cap is not ‘on’ then the film is exposing – bear in mind that only a 0.5mm slice of film is exposing if the film is not moving. The power winder drives the film continuously When the release button on the power winder is pressed the film will run past the slit at a given speed. This speed is determined by the % power level set on the speed controller. Normally an unmodified SLR will advance one frame at a time, this camera advances film continuously as long as the release button is pressed. There is an electronic speed controller connected to the winder The standard power winder is wired to a speed controller. The controller can be varied from 0-100%, the winder will move film from about 30% onwards. The film speeds for a given system are typically 15mm/sec @ 30% to 100mm/sec @ 100%. At 100% the power winder runs at the normal power level it was designed for (there is no overloading of the winder). The power level can be varied without wasting film by disconnecting the lower set of cables or during shooting for artistic effect. The power winder takes 4 ‘AA’ batteries, these power the speed controller also. All speeds are determined individually for each camera and a ‘cheat sheet’ is supplied to enable the photographer to set up a technically correct slit scan image i.e scale is preserved and the film is properly exposed. Many different scenarios with various subject speeds, lens focal lengths and distances between camera and subject are covered by the cheat sheet. The mirror is ‘up’ The SLR mirror reflects light into the viewfinder so that the photographer can see through the lens. On a standard SLR the mirror is always down except during exposure when it swings out of the way and allows light through the open shutter and on to the film. On this camera the mirror is up by default. A mirror down bush button has been added so that the ttl viewfinder can be used for focusing and composition. Precision focusing can be achieved as per a standard SLR. Releasing the push button allows the mirror to swing back to it’s up position and allows light to the slit. The push button is made from chrome plated steel with a wooden head (beech).
Auto aperture coupling is disabled On a standard SLR the lens aperture is wide open by default and only stops down to the selected aperture during the exposure. On this camera all K mount lenses will behave as manual lenses – the selected aperture is at all times the actual aperture (always in depth of field preview mode) . It is recommended to focus ‘wide open’ to achieve critical focus and then stop down to the desired aperture.
Here’s a short video showing the camera system..
I supply to order a limited number of these systems. For enquiries contact me directly at email@example.com. How Much? Slit-Scan kit including : body, speed control and power winder : €490 As this is a 1980’s camera system please note the body will be ‘used’. It will be clean and in good condition but may not be 100% perfect cosmetically. I have written an instruction manual which is also included – it includes how to easily calculate the required % power level for a range of focal lengths, subjects/speeds and distances. Note : Lens not included (K-mount lenses are inexpensive and plentiful on the used market – the 50mm focal length is most useful for slit-scan, I also recommend a wide (20,24 or 28mm) for slow subjects such as people walking, and a telephoto (100 or 135mm) for fast subjects (e.g horse racing)). Reliability? The pentax ME super is a sturdy and rugged camera. The slit-scan modification has simplified many aspects of the camera. There’s is no shutter or electronic light meter to fail and no winding cams/gears to jam as is common to happen on these old SLR’s. It drives film past a slit, that and the mirror down push button system is the extent of the moving parts. Every camera system sold is guaranteed for 12 months and any problem will be repaired/replaced free of charge. You can see more of my slit-scan photos on the gallery page here.