Before describing in detail the steps involved in processing movie films, it will be as well to make quite clear the essential difference that exists between the two methods of producing a positive suitable for projection.

The so-called reversal method is the one generally favoured by amateurs since, without any extra cost to themselves on development this gives a positive directly from the film loaded into the camera. This result is achieved by using a special type of emulsion which, when subjected to suitable chemical treatment, forms first a negative and then a positive image on one and the same strip of film. Films coated with this type of emulsion are referred to as Reversal Films and, generally speaking, they do not lend themselves satisfactorily for use as negative films.

Negative film is used in the Negative/Positive method which is akin to the technique of producing prints familiar to all still photographic workers. The film exposed in the camera carries an emulsion similar to that found on ordinary (panchromatic) roll films and, like a roll film, is developed to a negative. The negative is then printed in contact with a roll of positive film to produce a finished print suitable for projection.

Both methods of producing positives have their advantages and disadvantages, but unless more than one copy of the final result is required, the amateur is strongly advised to stick to reversal film. Even if extra copies are required, they can still be made without too much bother from this one reversal positive. Furthermore, as will be pointed out in the next section, reversal film may be expected to have a greater latitude in exposure, and a somewhat finer grain than the print produced by the negative/positive method. Against this, the very nature of the reversal film emulsion makes it impossible to reproduce accurately more than a restricted range in subject brightness levels. It is because of this restriction that the user of reversal film is warned of the difficulties of photographing subjects of long brightness range. Best results are obtained with diffused or fairly flat lighting.

Reversal material is returned after processing as a single film ready for projection; the negative/positive technique, on the other hand, produces two films, one a negative and the other a positive print. Only the latter is suitable for projection, however, and unless further prints are likely to be required, the negative inevitably becomes an encumbrance, and mayjust as well be discarded - except by the advanced or specialised worker for whom the negative has a particular value in editing or cutting his material. The usual practice here is to edit a print taken from the uncut negative and then to cut the negative to match the edited print. A second print is then made from the cut negative to show the film in its final edited form.