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Gradation

A film's gradation determines contrast


Gradation refers to how a film reproduces contrast - the range of light and dark tones in a subject that a film is capable of showing.

The extremes of tone in a scene are referred to as highlight and shadow, and all the tones in between the brightest highlight and the deepest shadow encompass the range of tones that is available for a film to record. Films differ in their ability to record tonal range.

Strong sunlight creates high contrast, requiring a fairly soft gradation film to show shadow detail.
Strong sunlight creates high contrast, requiring a fairly soft gradation film to show shadow detail.

THREE LEVELS OF FILM GRADATION

There are three levels of contrast range attributed to different films: soft, medium and hard gradation.

1. SOFT GRADATION FILM is low contrast film, and produces negatives (or slides) in which contrast between the light and dark parts is lower than it looked in the scene that was photographed.

Contrast is influenced by film speed. Most high-speed film has soft gradation. As film speed increases, contrast decreases even further. If a subject is quite contrasty, a soft gradation film will tend to reduce contrast.

2. MEDIUM GRADATION FILM reproduces the scene’s contrast pretty much as it appears. This doesn’t mean that the film will necessarily record the entire range of tonal contrast in a scene, but that the overall contrast of the scene will look pretty much the same on the film as it does to the eye - neither more nor less contrasty overall. If the contrast range of the film’s emulsion is the same as the range from highlight to shadow of the scene, a correct exposure setting will capture the entire range, with detail showing in both shadow and highlight areas.

Most popular, general-purpose films have medium gradation since accurate reproduction of a scene’s contrast is desired by most average photographers.

3. HARD GRADATION FILM produces the greatest contrast - that is, the negatives show higher contrast than was apparent in the scene that was photographed, meaning that only some of the tones found in an average scene are reproduced on the film. Photographers will employ a hard gradation film when their subjects are very low in contrast.

Films used for copying text or for copying ink drawings must be very high contrast. Microfilm is an example of a hard gradation film. Line film is another example, and is useful in applications where there is a need for pure black and white with little or no intermediate shades of gray. Photographic reproductions of line drawings in the graphics art field are made on this type of high contrast film to ensure clean dark lines on a clear white background. Usually, line film is developed in a high contrast developer.

High contrast caused by light rays striking the subject from the same angle, as illustrated by the museum spotlight shining on this dinosaur skeleton, creates dark shadows and bright highlights.
High contrast caused by light rays striking the subject from the same angle, as illustrated by the museum spotlight shining on this dinosaur skeleton, creates dark shadows and bright highlights.

FACTORS INFLUENCING GRADATION

Contrast can vary for any film dependent upon the following factors:

Light - Illumination of the subject may be contrasty (caused by light rays striking the subject from nearly the same angle - for example, the light beam from a single spotlight), which at its extreme means the subject will have bright highlights and dark shadows with no medium shades between, regardless of the film used. Subject contrast, then, must be taken into account when choosing a film. A low contrast subject on low contrast film may be too flat and washed out. High contrast scenes taken on high contrast film may appear too harsh and hard.

Exposure - Correct exposure will reproduce a scene’s contrast in accordance with the gradation of the film being used, but underexposure will produce negatives of higher contrast. Overexposing a scene will result in lower contrast negatives. Since the contrast of high-speed films is generally quite low to begin with, overexposure can cause an almost total wash-out of an image, rendering it flat. Such images have little contrast and appear to be fogged.

Film development - Fine grain developers will produce lower contrast than standard developers, and rapid developers result in higher contrast negatives. Longer development time, however, increases negative contrast. Shortening the amount of time that a film is in contact with the developer will decrease contrast in the negatives. Development temperature can also be a factor affecting contrast.

The subject itself - Contrast in an image can also be influenced by the subject matter. For example, a scene composed exclusively of black and white objects is inherently more contrasty than one composed of objects with a range of tones.