FILM STOCKS CHARACTERISTICS

Each film stock is identified by a number of characteristics; we can list them.

1. It is a camera film, duplicating film or projection film
2. It is black and white or colour.

1. If Black and white it is Blue, Blue and Green (Orthochromatic) or Blue, Green and Red (Panchromatic) Sensitive
2. If Colour it is masked or unmasked.

1. It is positive or negative or reversal
2. It is on clear base or coloured base
3. It has positive or negative perforations

You must remember that any film has characteristics from each category but because a film is positive, it might not have positive perforations. Therefore, we must go through each item explaining the options and the reasons for the characteristic.

1. If the film is a camera film, it will have a high emulsion speed. A duplicating film has low contrast, a positive film high contrast.
2. This needs no explanation.

1. The sensitivity to colour of a black and white film varies according to its use. A camera film must be panchromatic so that it reproduces the colours we photograph as the correct tones. Dark colours must look dark.
   Duplicate negative is colour sensitive because we can use it to duplicate colour film and require the correct tonal reproduction.
   Positive stocks are just blue sensitive because we use them to make prints from black and white negatives so colour sensitivity is not needed.
2. The dyes used in colour film must fulfil two criteria; they must be suitable for colour reproduction and they must be able to be produced by the reaction of the couplers on the film with the colour developer.
   This second criterion means that a dye that gives excellent colour reproduction might not be suitable for use.
   We must use dyes that are not perfect. The most common failing in a dye is unwanted absorption. For example, a Magenta dye should only control green light; in practice, it also might control Blue light. This causes problems with colour reproduction. Correction can be made by masking the emulsion. This involves having couplers (these are chemicals that produce the dyes in the film) that are coloured. Masking can be seen by looking at a processed piece of colour negative film. The film is an orange colour which is the magenta and cyan masks which are yellow and pink giving the orange colour. Masking is only used in camera and duplicating stocks as the mask would reduce the light passing through a projection print necessitating more light from projectors.