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What is the Slide and transparency films?

Color films designed to give positive images direct often include the suffix chrome in their brand name rather than color, which is used for negative types. Chrome films are also collectively known as color reversal films, because of the special reversal processing they must be given. Results from rollfilms and sheet films are normally referred to as transparencies, and 35 mm results as slides. Traditionally these materials were mainly used by the professional

The amateur market for slide film has completely died out and digital is fast replacing transparency in the commercial world also. Slide and transparency films have high image resolution (unlike most prints which have had to pass through a lens twice) and so traditionally were preferred for the printed page. Today, however, digital files are what the commercial magazines and newspapers use. Advances in digital imaging have meant that images can simply be transferred via the internet in suitable image files and then go straight to print.

All reversal films have a multi-layer structure, making use of blue-, green- and red-sensitive emulsions, and most have yellow, magenta and cyan dye-forming couplers, similar to those in colour negative film. However, results have stronger contrast and saturation of colour, plus a lack of ‘masking’ (see Advanced Photography), which means that there is none of the overall pinkish tint characteristic of colour negatives. Viewed on a light box or projected as slides, reversal film images show a wider range of colours than it is possible to achieve on paper prints.

During the first part of processing only black and white developer is used, forming black silver negatives in the various layers. Dyes are then formed where the unused halides remain so that when all silver is removed, a positive, correct-colour image remains.

All reversal colour films need chromogenic processing using developing kit E-6 and this, like C-41 for negatives, can be carried out by photographer or laboratory.

Colour balance. Colour balance must be more accurately matched to type of lighting than with negative materials, as corrections are more difficult. They can be corrected by digital means or printing but if you are using slide film to project images this becomes more complicated. The majority of colour slide films are balanced for daylight and flash but there are also several films designed for 3200 K tungsten light. Daylight film needs a bluish filter if used with tungsten light; tungsten-balanced film needs an orange filter with daylight or flash. Image colour is easily ‘burnt out’ by accidentally over-exposing or darkened by under- exposing, so here again you have to be more accurate – little correction is possible later, apart from some speed-rating compensation of complete films during processing.

Film speeds and colour contrasts. Again, the widest range of reversal films is available in

35 mm format, from ISO 25 to ISO 1600. Most (up to ISO 1000) are also made as rollfilms. Sheet films range in speeds from ISO 64 to 160. Tungsten-balanced films are typically ISO 64 (many of these have been discontinued). Most reversal films of ISO 200 or faster can be up-rated and then push-processed to double their normal speed rating – either to correct overall exposure errors or help when you shoot in dim lighting. Some make a feature of their up-rating potential and allow four times the speed rating shown on the box, although changes in image contrast and increased graininess become your limiting factors.

Processed results from reversal films are brighter and richer in hue than colour negatives. They must have the brilliance of appearance expected in a final image, as opposed to an intermediate tailored to match up with the characteristics of neg-pos-colour printing paper later. Different reversal films produce subtle differences in image colours owing to different image dyes used by the manufacturer.

According to subject and mood you can shoot with a very saturated colour film; or one saturated but ‘warm’; or one specially optimized for skin tones; or again film giving a slightly warm colour balance for outdoors in cloudy conditions. Take care though not to mix reversal films from various manufacturers when covering any one assignment. Shots showing differences in hue and contrast then stand out like a sore thumb.

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