6. Insert centre spool into shell; the first 2 in. of film must extend from the light trap.
7. Close cassette.
2. In the case of bulk film prepare the length to be used as described on page 26. When using darkroom refill
remove its wrappings. It is useful to fold the first ½ in. (1 cm.) of the beginning of the film slightly backwards. It
prevents its slipping away.
4. If the centre spool is fitted with a film catch, thread the tapered end of the film into it. In cases where the centre
spool is fitted with a spring, thread the end under it and fold it sharply back. If the centre spool is without any
suitable fitting to hold the film, it has been proved best to wind a 1½ in. (4 cm.) piece of adhesive cellulose tape
round the centre spool, so that on either side about ½ in. tape is used to secure the film (see page 29).
5. Wind film on centre spool moderately tightly. Care must be taken to see that the fingers do not come into contact
with the emulsion only the back and sides of the film being touched.
7. When using some makes of cassettes, it is essential to fix the top or bottom cover to the shell, preferably with a
length of adhesive cellulose tape.
Loading Cassettes with Daylight Refills
1. No darkroom is necessary.
2. Remove wrapping and label of refill.
3. Open cassette.
4. Introduce refill into shell of cassette; the first 2 in. of paper has to extend from light trap.
5. Close cassette.
6. Pull out paper-leader and 2 in. of film.
7. Cut off paper-leader.
4. The original centre spool of the cassette is not needed and may be kept separately.
5. When using some makes of cassette, It is essential to fix the top or bottom cover to the shell, preferably with a
length of adhesive cellulose tape.
The Choice of Material
There is no such thing as a "best" film for any or every kind of picture. Each type of film has certain characteristics.
COLOUR SENSITIVITY. Practically all 35 mm. films are sensitive to all colours. They are known as panchromatic.
Some types, particularly those of high sensitivity, are especially sensitive to red. They are thus very suitable for use
with artificial light which is richer in red than daylight.
INFRA-RED FILM. Infra-red film is a negative material which, unlike panchromatic films, is made sensitive to infra-
red rays, which are not visible to the human eye. Special applications of this material: photography by "invisible"
light, long-distance shots, fog or mist penetration, scientific copying and research work.
ORDINARY FILM. For copying black-and-white objects (books, ledgers, etc.) a positive film can be recommended.
Besides its qualities of fine grain and high brilliancy, it possesses the further advantage that it can be handled in an
amber darkroom light.
SPEED. The sensitivity of film materials to light in general is expressed by various scales, such as BS, ASA, DIN, and
so on.
While a scientifically correct conversion of one speed rating system to another cannot be made owing to their
different principles, the list on page 32 gives some guidance as to their practical relationship.
Each value represents twice as fast a film speed as the one above it. In some systems doubling film speed means
increasing the speed number by 3 each time (BS Log., DIN), in others the speed itself is directly proportional to the
speed number (BS Arith., ASA, Weston).
Slow films of less than about 40-80 ASA can be usefully employed for scientific photography, copying and
architectural details. Their main advantage is in their extremely fine grain. making special development unnecessary.
Their disadvantage is in their inability to cope with live subjects in other than exceptionally favourable lighting
conditions.
Medium films of 80-160 ASA are the right material for the beginner, and can be well employed for any of the
average subjects. Their advantages are: reasonably fine grain without the use of too complicated methods of
development, correct tone rendering, good resolving power. Disadvantage: further loss of speed if fine grain
development has to be employed for the sake of big enlargements.
Fast films of 200 ASA and over for high-speed sport shots, interiors, stage pictures and night photography.
Advantages: increased sensitivity for red (artificial light), use of smaller apertures (increased depth of field).
Disadvantages: graininess which, however, can be improved by special methods of developing, at some cost of
speed.
