Film cartridge
In analog photography, a film cartridge is the largely light-tight housing for 35mm films in which the film is assembled . This type of film 135 allows the exposure of 24 × 36 mm material (lengthways) per 8 perforation holes (on each side) but also other formats, which is seldom handled. In special cartridges, you can assemble the meter yourself.
The film cartridge is made of sheet metal or, rarely, of plastic with velvet covers on the film slot. As a rule, a checkerboard print, the so-called DX coding , enables the camera to recognize the film sensitivity and other properties of the film (from 1983). Inside the cartridge there is a spool - the so-called supply spool - on which the film is wound. Usually after an image has been exposed, the film is transported image by image onto a storage reel. After the last picture, usually when the end of the film is reached, the film in the camera is rewound (almost completely or completely) back into the cartridge. Very few camera types first rewind the film completely and then the exposed images back into the cartridge; The advantage is that the exposed cadre (except for the last one) are light-protected in the cartridge, the disadvantage that the loaded camera can be sabotaged by opening before exposure.
In most cameras, film is transported from left to right and, if manually, with the right thumb. On the Rollei 35, however, to the left. The resulting different orientation of the recordings on the film is visible in the position and the direction of the progression of the production-related numbering on the edge of the film in relation to the negative image, as well as a laboratory-side framing of slides, usually automatically numbered at a corner.
For film development , the film cartridge can be opened in the darkroom or in a changing bag and reeled into a developing can, which can then be used, for example, in a tier tank for developing several films (can development ). Films are developed by machine in photo-technical copiers and at "1-hour photo services", the so-called minilabs. Specialist laboratories work with special laboratory machines that can be adjusted individually depending on the development process and film format, as is possible with can development.
The cartridges can typically be opened relatively easily by squeezing the cylindrical shell toward the film slot and firmly pressing the top of the film spool onto the table above. There is practically no deformation of the parts that can also be reassembled. The profiled end rings can be chrome-plated and painted black, as can the inside of the cartridge casing to dampen light. The only one-sided projection of the core from the cartridge body helps to orient the cartridge in the dark and can be used to rewind the film into the cartridge using the thumb and forefinger.
Contamination of the film slot with sand must be avoided. Kodak cartridges have rings made of thinner sheet metal at both ends, the crimping of which means that they cannot be reused after opening.
The film cartridges that are still used today were developed by IG Farben in 1936 .
In the past, the end of the film was attached to the spool cores - always made of plastic - in the middle by a piece of adhesive tape (crepe paper) that was about 1 cm narrow around the core. Cores later came up with a slot equipped with two barbs on the inside, which inevitably grasps and holds a film end that is tapered to a tab (about 1/3 or 1/4 width) and has a suitable hole Pull out the train in a controlled manner. The film is usually attached to a recycled ready-made cartridge using an adhesive strip.
