حساسية الفيلم .. كتاب فن التصوير الفوتوغرافي

Film sensitivity: Differences in laboratory processes when making films form different types of films. For example, the sensitive layer in black and white films is sensitive to different colors in different degrees according to the strength of each color, thus producing different shades of gray. This is the basis of the process of image formation. If the film was sensitive to all colors to the same degree, we would end up with a gray negative with unclear features.

The panchromatic film that you use is sensitive to all colors of the visible spectrum, because the word panchromatic means all colors. . However, when the sensitive film layer was invented, the audience of photographers was so delighted that they gave the film the correct “color” label. Over time, this label proved incorrect because this sensitive layer was sensitive to some colors of the visible spectrum only, and not others, namely blue, green, and yellow, but it was useful. Great for several years until its successor was invented

Panchromatic films are sensitive to colors in different degrees, each according to the quantity and type of materials added to the sensitive layer, according to the manufacturer. There are highly sensitive layers that sense the red end of the color spectrum as well and are better sensitive to artificial red colors

Each film has a certain job that it can do better than the rest of the films. And if you choose the appropriate film for your subject and use the appropriate exposure, you will undoubtedly get the best results. One of the most important characteristics that must be preserved and not always changed is the speed of the film. Use a film with a certain speed and produced by a certain company all the time, and you will reap the best results. Your use of a specific film all the time makes you understand all its characteristics, and thus you can control the result you want.

Film makers in the past had their own systems for measuring the sensitivity of films, but at the present time there are two main measures to measure the sensitivity of films, namely 1 - ASA for short, American Standards Association, i.

The two systems are identical in terms of the standards they use, even if the name differs. We note that all exposure meters and all color and regular films have the two numbers together, the AZA number and the DIN number.

Films are made at three main speeds: - Slow films 20-64 AZ 10 or 14-19 DIN B - Moderate films 80-200 AZ 10 or 20-24 DIN Fast films 400 AZ or above or 27 din or more. C -

Each of these groups has characteristics that differentiate it from the other group. Among these characteristics is that the faster the film speeds up, the more granules will appear on its surface caused by silver halide crystals gathering on the negative during endorsement. These granules will appear in the enlarged image in the form of dots that cover the entire image. However, the fast movie industry has evolved to the point that you may not notice these grains even at the magnifications

In general, slow movies are the best. The best in this regard because it is completely free from the phenomenon of granules

The quick film is distinguished from other films because it is suitable when filming in poor lighting conditions or when the difference in lighting levels in a single shot between highlights and shadows, so it records the details on both sides with the same clarity. Lighting with confidence. Whereas a mild film limits your shooting freedom. Its exposure range is narrower than that of fast film, but it is more popular among photography enthusiasts because it is the middle choice between fast and slow film. Its drip-free and reasonable speed make it ideal for general photography subjects that you will deal with

a

Slow motion films between 20-64 aza are known as high-contrast films because of their narrow exposure range. It needs a great deal of care to reduce light contrast. to reasonable limits. The use of these films is limited to special shooting conditions, for example, when there is a need to take accurate details of a subject. In general, we find that fast films are more lenient than others in terms of lighting errors. It can record the snapshot, whatever the level of lighting, but the level of image quality as a whole will be affected in some way. Lighting errors appear in slow films clearly, giving negatives that are not printable. In general, to get good quality pictures, you must accurately determine the amount of light needed by exposure meters.