الأنواع المختلفة للأفلام الفوتوغرافية - ١ - تجهيز المخبر .. كتاب التصوير الضوئي

Different types of photographic films - 1 - Preparing the laboratory .. Choosing and using materials .. Book of photography

- Different types of photographic films:

The film consists of a transparent substrate on which lies an emulsion of silver bromine suspended in gelatin. The substrate is most often made of cellulose triacetate, but there are also films whose substrate is polyester.

- Speed ​​and grain of films.

Sensitive speed of the film
Slow
Medium
Fast
Very fast

Most often films are classified according to their sensitivity to light, which photographers call speed. The speed of the film increases as the silver bromine grains in the compound increase. When the silver grains turn into metallic silver to form the image, this grain is given, which appears clearly at high magnifications of the image. Fast films have a thick layer of the compound, which increases their speed but causes the light to spread, which spoils the finest details of the image. In general, we use slow films when we intend to make large-length enlargements (e.g., 10x, ten times larger than the negative), while fast films are used for objects with poor lighting. Speed ​​and grain are closely related, and if we gain on one side, we lose on the other. There are some more subtle differences between films: slow films tend to give more contrast than fast films. Although exposure has an important effect on the contrast of the negative, it is very difficult to get a very contrasty image on high-speed film.

- Black and white film:

All films in common use are sensitive to all visible spectrum radiation. For linear professions and some copying and transfer work, there are films that are only sensitive to violet-blue and others that are sensitive to violet-blue and green.

- Color film:

The two major families of color films are reversible film and negative film. The latter is usually used for enlarging on colored paper while reversible film produces magic lantern slides (positive images). However, there is the possibility of drawing on paper from magic lantern slides and making positive images from negatives.

- Color negative film:

All negative films include an orange mask that gives a special look to the negative image and significantly improves the saturation and color accuracy of the positive image if we want to make it later. Color negative films have a speed between 64 and 125 ASA.

- Reversible colour film:

These films are divided into two main groups: the first group includes films in which colour problems are present in the compound and the second group includes films to which colour problems are added during processing: for this reason this last group cannot be processed by the user device. The speed of reversible films starts from 25 up to ASA 500 or more. The faster films are usually less contrasty and have a more pronounced grain: however, this relationship is less clear than in black and white. It must be said that the decrease in contrast is often compensated by better colour saturation. The films currently on the market can be controlled for the duration of the image capture, which was not the case in colour films several years ago.

- Daylight and artificial light films:

The colour films are temperature-balanced according to the colour of the illuminated object (see page 231). There are two types of reversible film: Daylight (5400) suitable for natural light and flash light, then artificial light (type A or B) Incandescent light sources with 3400 or K3200. Incandescent and quartz-halogen (gas) lamps used in photography have a colour temperature of K3200.

- Special films:

These films for special applications can only be obtained by ordering from the manufacturer. They are usually delivered in 35 mm film strips (30,50). Other films
are available in sheet form for professional use.

- Special black and white films:

- Infrared film:
It is sensitive not only to the visible spectrum but also to the nearer infrared radiation. It is usually used with a dark red filter that prevents the blue violet and green radiation from being imprinted on the film. For scientific uses, a filter that is completely opaque to visible radiation is used. For ordinary photography, a dark red filter is sufficient. Landscapes captured on infrared film have a very special nature and scene: the blue sky is black, the atmospheric veil is noticeably reduced and the green meadows become white as snow. The grain of the infrared film is very visible. Read carefully the instructions given by the manufacturer and remember to apply the calibration corrections.

- Infrared photography:
The common film is sensitive to all radiation of the visible spectrum - whose wavelengths range from 400 to 720 nanometers. After 720 nanometers, infrared radiation can affect specially prepared photographic sensitive compounds.