The core of the project is the camera module (I used the 1.3 version) for the Raspberry Pi. The camera module is broadly supported by many Raspberry Pis, and surely also by the Zero. It's installation and use is straightforward and there are many readily available tutorials for this. The sensor fine tuning will be discussed deeper in following log entries. This is a very cheap solution specially when overseas compatible replicas of the module can be found for as little as $2.5
Be sure to grab a couple (I bought 4 units at once) as the sensor is extremely sensitive to handling and static electricity discharges. I destroyed a camera module when unmounting the lens.
The default lens mounted on the camera module, appart from being of poor quality, is incompatible with our project. Recalling from the first log entry, the in-built lens alters the focal length of our optics and it's impossible to use in combination with the lens of the camera.
Here comes the most delicate part of the project: the unmounting and adjusting of the camera module lens. The camera modules I bought had the lens glued to the sensor mount. It can be forced and unscrewed counter clockwise with a pair of tweezers exposing the sensor itself.
Note the redish IR filter embedded in the sensor. Some webcam digital sensors include this filter in the lens, which make the sensor capture IR light and therefore distort the colors.
The sensor has to be precisely mounted on the focal plane of the camera, and yet as seen previouslt will cover only approximately a quarter of the 8mm film frame. I used some epoxy to adjust the sensors position while streaming the resulting image live. More on this on later entries.
The 8mm film cartridge compartment offers enough size to theoretically fit all required components. If atention is paid to cabling and positions it can host the camera module, the Raspberry Pi Zero and the power bank with its electronics.
The trigger contact of the camera can be directly recycled with minimal soldering to use it as an input for the GPIO pins. The handling of the original super 8 camera (push and hold button to record) can be exactly replicated.
Finally all the power is provided by a 3500 mAh power bank, which offers enough power for some minutes of recording. I did not measure the endurance of the power supply precisely but it last for around 15 minutes of video with the factory charge. Remember 15 minutes was the maximum duration of the 8mm film shot at 24 fps as indicated by an ingenious turntable-like advance counter.
As this is a project I considered very likely to fail due to the precise optical and electronical tuning involved I didn't want to spend too much buying an iconic Super 8 camera (such as an old beautiful multi-lense Bell & Howell or some spring-loaded Bauer camera). After a quick research on my favorite second-hand marketplaces I found out that early '80s soviet cameras have the best price-quality value.
A kind gentleman from Latvia was indeed selling an apparently fully functional (I never checked it) Avrora (Аврора) 215 camera for a fair price including lense and carrying bag accesories.
This camera was manufactured in the Leningrad Optical Mechanical Association (ломо) between 1978 and 1981, the same place the now hipsterly known lomography takes its name from. There were two versions, one labeled and marketed for the 1980 Summer Olimpic Games in Moscow and the other one branded for export. The one I acquired belonged to the latter series.
The main difference between analog motion film capture and digital film capture lies on the sensor used. Analog pictures are captured over a continously moving stripe of photosensitive material, while its digital counterpart only requires a light sensitive electronic sensor.
Therefore, the core of the project will be replacing the analog film -and its mechanism- by a light sensitive sensor.
Let's start by a brief introduction to optics:
(Image courtesy of Expert Photography)
A camera is nothing more than a tool that concentrates the light reflected by the objects we want to photograph over a capturing surface through the use of lenses. The amount and the way this light will be captured is defined by the quality and characteristics of the lens and the capture surface. In order for this project to suceed two factors have to be taken into account:
The focal length: The distance from the lens optical center to the place on the sensing surface in which the image will be "in focus". We cannot do much about it, it is defined by the lens we use and in the case of every camera it is fixed. It can only be altered by optical means. We just need to worry about setting our sensor on the same focal plane of the analog film.
The size of the sensing surface: This will be the most determining feature and we indeed have control over it. Super-8 film has a dimension of 4.01mm x 5.79mm. The whole viewfinder mechanism, optics and zoom of the camera is designed to expose this surface.
However, digital camera sensors are offered in many sizes (usually denoted in inches). The professional reflex cameras would use a so called full-frame sensor (the same size as the 35mm analog film), although more common digital single lens reflex (DSLR) cameras may fit a half-size or quater-size sensor. However, cell-phone, webcam and cheaper camera fit ever decreasing sizes of sensors. Which in contrast are less sensitive (the less surface they have, the less light they capture). In fact, the Raspberry Pi Camera module we intend to use suits a Sony 1/4" sensor, which is almost a quarter of the size of the intended 8mm film.
This will cause our image to be cropped (the effect of zoomed in) and there is nothing, except using a more expensive and bigger sensor, we can do about it.
Taken into account this theoretical approach to our project it is time to gather the materials, and start the dissassembly and assembly.