Film copy
A film copy is a duplicate of a film. Uncut or cut and mounted film material ( negative film , positive film or reversal film ) can be copied . The film copy is made with negative film, positive film or reversal film. Depending on the process used, a distinction is made between optical and contact copies .
The image quality ( image status , sharpness , resolution, contrast range , color fidelity ) of a film copy is always poorer than that of the film material from which it originates (see generation of copies ).
Contact copy
For a contact copy, the film material to be copied is pressed onto the unexposed film material (copy film) (image layer on image layer), with positioning elements for guidance. The film strips thus brought into contact are drawn past a light gap. This is why one speaks of “pulling” a copy. With continuously acting (ring gear) systems, the copying speed can be up to 10 meters per second. Step-contact copies are particularly suitable for large-scale projection, but usually cost more.
Optical copy
For an optical copy , the original material is imaged on raw film with a lens. Both films run in opposite directions. This is done in a special copying machine , the film drives having higher grades, or copying systems for format changes. Because the film drives can run separately, switching, tricks and corrections are possible, for example to the image size. There are also continuously operating optical copying machines in which the direction of travel of the films is in the same direction, namely in the combined reduction-duplication such as 35 → 4 × 8, 35 → 2 × 16, 32 → 2 × 16 or 16 → 2 × 8. 32mm film as a pure copy format has not been used since the 1980s.
Dry and wet copying
Until 1957 only dry copying was used. Individual experiments with humidification and wet wiping devices could not spread.
Then the first results of copying tests under liquids were published. It has been found that liquids whose optical refractive index is close to that of the image layer and the film support fill in fine scratches and scrapes and form a single optical medium, with which they are said to not copy. Dust particles are also partly washed away and partly rendered ineffective for copying. Finally, there is no static charge on the films, which means that even less dust reaches the film surfaces. Deep scratches that pierce the image layer cannot be made to disappear. A number of suitable copying fluids have been suggested, some of which are carcinogenic and toxic. In particular, perchlorethylene is in common use, which requires effective extraction and recovery of the vapors.