How to choose film?

Beginners who can shoot black-and-white films and learn to develop and enlarge photos by themselves will be of great help to understand and master the use characteristics of photosensitive materials and train to observe and understand the relationship between light and shadow from different angles. The selection of black and white film can be considered from three main characteristics of film: 1. Color sensitivity, 2. Sensitivity and 3. Particle size.

The color sensitivity of black and white film can be divided into three basic types: panchromatic film, orthochromatic film and infrared film. The sensitivity of panchromatic film to all visible light is roughly equal to that of human eyes, and it is also the most commonly used black and white film for general photography. Most of the films sold in shops are full-color films, generally referred to as "pan" films, and most of them are marked on the packaging. A positive film is a film that is sensitive to all colors except red. Before the invention of full film, positive films were widely used, but today they are only used for special purposes. Infrared film is a special film sensitive to infrared spectrum, which is invisible to human eyes. When the mist blocks visible light, it can penetrate the mist and clearly shoot the distant view. In addition to its application in scientific experiments and military applications, infrared film can also produce special image effects completely different from panchromatic film.

Black and white dye film is a black and white film made by color film technology. It uses silver salt as a photosensitizer, and in the development process, silver is removed, leaving a dye image. It is unique in that it adopts the same C-4 1 treatment process as color negative, and the treatment can be completed through a color printing shop. This kind of film is characterized by silver-free film composed of dyes, fine particles and large tolerance. Its calibration sensitivity is mostly a variable value, which can be adjusted according to different uses.

Whether you choose black-and-white film or color film, you need to consider the sensitivity and granularity of the film and the relationship between them.

The sensitivity of film refers to the sensitivity of photosensitive materials to light, also known as film speed. Film sensitive to light, such as film with sensitivity greater than 400, is called fast film. On the contrary, films that react slowly to light, such as films with a sensitivity lower than 50, are called slow films. Generally, films with sensitivity 100 ~ 200 degrees are called medium-speed films. The sensitivity of the film is provided by the film manufacturer. There was no uniform label in other countries before. In 1980, the international standard sensitivity is implemented. It is based on ASA system used in America and d in system in Germany. The symbol is ISO, written as ISO 100/2 1, with 100 in front being the ISO(ASA) value and 2650 behind. Generally, high-speed film needs less exposure and is suitable for shooting high-speed moving objects, such as sports, in low light. However, the granularity of high-speed film is relatively coarse, not as fine as that of low-speed film, and the photos enlarged with it appear coarse and lack of detailed texture. If you want to take photos with high magnification, rich details and fine particles, you can choose a slow film with a sensitivity below 50. Slow-speed movies can sometimes use slow shutters to display dynamic effects. Compared with the past, the graininess of the film has been greatly improved. The quality of films between ISO100 and 400 is good, which can be applied to almost all kinds of occasions and shooting conditions.

Color film can be divided into two types, namely reverse film and negative film. Color reversal film, sometimes called slide, is a kind of film that can directly obtain color transparent positive images after reversal development. The color reversal film can be viewed by projecting the image directly onto the screen through the slide projector or on the observation light box. It can not only print and play photos directly, but also be used as the original film for color separation and plate making. The color reversal film is truly saturated, and the clarity and sharpness of the image are relatively high. However, compared with color negative film, the exposure latitude is relatively narrow, a little insufficient or excessive, which will affect the imaging quality. Therefore, making a reverse film requires very accurate exposure. Color negatives are mainly used to print and play color photos. After shooting and developing, color negative with orange cover can be obtained, whose light and shade are opposite to the subject, and their colors are complementary. The advantage of color negative film is that exposure latitude is big. Generally, the exposure is less than one level or more than two levels, and satisfactory images can still be obtained. In addition, color negatives are quite universal to the change of color temperature, and the color balance and contrast can be adjusted again through the color filter of magnifying glass when printing and playing photos. The English brand suffix of COLOR negative film is color, and the suffix of reverse film is krom. On the film box marked in English, negative film and negative film can be distinguished according to the above two suffixes. In addition, according to the color temperature balance, color films can also be divided into two categories: daylight type and illumination type. Daylight color film is suitable for shooting under the illumination of sunlight or electronic flash with a color temperature of about 5500K K, and light color film is suitable for shooting under light sources such as iodine tungsten lamp with a color temperature of about 3200K. If daylight color film is used for shooting under the light with a color temperature of about 3200 K, the picture will appear orange-red, and a blue color temperature conversion filter should be added in front of the lens. On the contrary, if you shoot with a light film in the sun with a color temperature of about 5500K, the picture will be blue, and an amber color temperature conversion filter should be added in front of the lens to get accurate color reproduction.

When choosing color films, there are also professional films and non-professional films. Non-professional films are mainly supplied to the civilian market, and the turnover and storage cycle of the market is long. Therefore, films do not reach the best color balance when they leave the factory, but let them have a mature process in the future. Professional film is to set the color balance to the best state when leaving the factory to ensure the most accurate color reproduction. Therefore, professional films need to be stored in the refrigerator before use to ensure their quality.