Classification of films

Commonly used are 120 film and 135 film.

135 film is often used, and 135 film is suitable for various models of 135 cameras. This film is 35 mm wide and 160 ~ 170 cm long. There are holes arranged regularly on both sides of the film. Generally, 36 3.6 cm× 2.4 cm negatives can be taken, and 20, 24 and 72 exposures can also be taken 135.

120 film can take photos of different sizes according to different 120 cameras, including 16 negative (the frame is 4.5× 6 cm); Shoot 12 negative (6× 6 cm); There are also 10 negatives (6×7 cm) and 8 negatives (6×9 cm). The length of 120 film is generally 8 1-82.5cm, and the width is 6.1-6.5cm.120 film. How many negatives are taken depends on the camera model. According to the photosensitive speed, there are iso 100, iso200, iso400 and so on. When the value is doubled here, the exposure required for exposure is also doubled. The larger the value, the faster the speed. Of course, many other speed expressions have been used before, such as American ASA system and German DIN system (customized). China adopts GB (national standard) system, which is equivalent to DIN system. According to GB system, it is divided into fast film (above GB24), medium speed film (GB2 1) and slow film (below GB 18). Every time GB3 is increased, its sensitivity is doubled. For example, the sensitivity of GB24 film is twice that of GB2 1 film. Various sensitivity standards can be converted to each other. ASA 100 is equivalent to GB 2 1 or 2 1DIN.

Negative films are classified according to exposure speed (ISO), ranging from ISO25 with the lowest speed to ISO3200 with the highest speed. Generally speaking, the lower the sensitivity, the finer the picture quality. According to the film size, there are 120 (large film), 135 (most commonly used, film width is 35mm), 10 (small box type), and other 4*5 or 8* 10 large films used for shooting advertisements or large posters. There are black and white negatives, color negative, infrared negatives and so on. Color negatives adjust the tone of photos according to different light sources, which are divided into sunlight films and lighting films. If you use lighting film to shoot a scene in the sun, the tone of the photo will be blue.

The commonly used negative specification is 135. With the continuous popularization of digital photography, there are not many negative films, and negative films still have their irreplaceable advantages. For example, the negative area of 135 is larger than that of most digital cameras (digital media). If you want to take large photos, it is better to use negative films. In addition, the negative image has a strong sense of layering and natural colors (colors generated by analogy). Especially in the case of dark light, the exposure and shooting time will be longer, or the film will be developed rationally (increase the developer concentration or lengthen the development time), such as KodakTri-X400 developed rationally to iso 1600, and even KodakT-maxp3200 developed rationally to iso6400, but long-term exposure will produce a lot of noise in digital photography, so some photographers still insist on it.

Although filming can produce high-quality photos, you need to be familiar with darkroom skills. Generally speaking, it is difficult for fast film shops to give full play to the advantages of negative films. Therefore, photographers who use negatives had better print their own photos. For example, they can expose photos in different areas and adjust the contrast and cropping of photos themselves. In addition, because the chemicals used in black-and-white printing are far less toxic than those used in color printing, and the printing process is simpler, many people do manual printing in black-and-white darkrooms, and most of the color negative films use automatic printing machines. There are black and white films, color films and so on.

1. Black and white film: According to its sensitivity to color, it can be divided into panchromatic film, dichroic film, color-blind film, infrared film and X-ray film. Full color film is usually used. Panchromatic film is aimed at all kinds of colors in nature. Red, orange, yellow, green, cyan, blue and purple can be displayed in different shades of black. In visible light, the color separator can feel blue and purple, yellow and green, but not red. This kind of film is often used for printing and plate making, and sometimes for landscape photography. Color-blind film is sensitive to blue-violet light in visible light, but insensitive to green light and red light, and is generally used for copying documents and black-and-white negatives. Infrared film, specially used to feel light with longer wavelength than red light, is generally used in aviation and military photography.

Selection of black and white film: How to choose low-speed, medium-speed or high-speed film depends on different requirements such as shooting object, shooting conditions and final photo magnification.

In general, when shooting outdoors, the light conditions are good, the scenery is bright and the contrast is large, so it is appropriate to choose 2 1DIN medium-speed film. If the contrast of the scene is flat, you can choose a low-speed film with a slightly higher contrast.

When shooting indoors, if the subject is dynamic, whether using natural light or lighting, we should choose a film with high sensitivity to avoid affecting the image level due to insufficient exposure or blurring the image of dynamic objects due to too long exposure time. When shooting with flash, generally choose 2 1DIN or film with higher sensitivity, so that not only the sensitivity index can be larger, but also its tolerance is large because of high sensitivity, which will not cause excessive contrast of the negative film.

In sports shooting, it is generally not suitable to use flash. Sports shooting is dynamic, so we should choose films with high speed sensitivity (such as 24DIN and 27DIN).

Generally speaking, stage photography should not use flash, but must use film with higher sensitivity.

Shooting portraits, still lifes and landscape photos requires rich layers, delicate silver lines, strong texture and pleasing colors. Try to use low-speed and medium-speed films.

2. Color film: Color film for photography includes color negative film and color reversal film.

(1) color negative, which is a developed negative image with complementary colors of the original color. Color negative is mainly used to make color photos; And you can print and play black and white photos directly, but the level and contrast of photos are affected to some extent. The sensitivity of color negative film is much smaller than that of black and white film. The negative color deviation is caused by the influence of color temperature and surrounding environment when shooting, but different color filters can be used to correct it in photo production. Color negative film is one of the most widely used color films.

(2) Color reversal film, through the process of reversal development, can obtain the same color positive image as the subject. The color image, color reproduction and image clarity of color reversal film are better than those of color photos, and printing with color reversal film is better than that of color photos. Color reversal film, its color is true, bright and full. Strict requirements when shooting, small sensitivity and accurate exposure. If the exposure difference is 1/2 times, various colors, densities and layers will be obviously affected. Film has different sensitivity to different colors of light, which is also a criterion for evaluating color film. The red color of Agfa film means that he is too sensitive to red after the whole exposure and development. Distort the color.