FILM SPEED, CONTRAST, GRAIN, RESOLVING POWER.
Generally speaking, low speed goes with greatest contrast, finest grain and highest resolving power and vice
versa. The film speed in the top row points to the corresponding contrast, grain and resolving power. The
contrast row shows (from left to right) how high contrast becomes medium and low as speed shows. The grain
row shows (from left to right) how fine grain turns into medium grain with growing speed and finally the
resolving power row shows the the decrease of resolving power (number of lines) with increase of film speed.
The bottom row indicates the type of subjects for which films of the various speeds are best.
Colour Film
These films produce an image in colour after appropriate processing, corresponding directly or indirectly to the
natural colours of the subject. From the practical point of view, colour film is as easy to use as black-and-white
film needs a little more care in exposure. Processing is more complex and is often carried out by the film maker
or specially appointed processing laboratories.
There are two basic types of colour film : reversal and negative.
Colour Reversal Film
This produces a colour transparency on the actual film exposed in the camera. This transparency held up to the
light shows a positive image with all parts of the subject in their original colours. It can be viewed in a suitable
transparency viewer with a magnifier or it can be projected in a slide projector to give a large and brilliant
picture on a screen.
There is little doubt that the projected image is the most natural and best for showing colour.
Although the colour transparency is an end product, it can still be used to make:
(a) duplicate positive colour transparencies,
(b) a black-and-white negative which can then be used to produce black-and-white prints or enlargements,
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