What do you mean by the degree of the film? What does it stand for?

Sensitivity, also known as ISO value, is a measure of the sensitivity of negative film to light, which is determined by the measurement of sensitivity and several values, and has recently been standardized by the International Organization for Standardization. For a negative with low sensitivity, it takes a long exposure time to achieve the same imaging effect as a negative with high sensitivity, so it is usually called a slow negative. Highly sensitive negatives are therefore called fast negatives.

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.

There are 120 (large membrane), 135 (most commonly used, with a membrane width of 35mm), 1 10 (small box type) and so on. , and there are 4 "* 5" or 8 "* 65438 used to shoot 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.

Extended data

Photosensitive characteristic

Photosensitive properties include: sensitivity, contrast, fog, latitude, maximum density, resolution, granularity, color sensitivity and so on.

speed

Sensitivity is the sensitivity of film to light, and it is also the photosensitive ability and symbol of film. Film can be sensitized in weak light, which is called high-speed photosensitive (fast) film; On the contrary, films with low sensitivity should be shot under strong light. If you shoot films with different sensitivities under the same light, you should change the aperture or shutter speed of the camera.

In other words, the film with high sensitivity has a smaller aperture and a faster shutter speed; Low-sensitivity film, on the other hand, has a larger aperture or a slower shutter speed.

Film sensitivity is expressed in ASA or ISO (ASA and ISO refer to different standards). It shows the sensitivity of film to light, which ranges from ISO25 to ISO6400. The higher the film sensitivity, the more sensitive it is to light, so it can be shot under weak light source; But the higher the sensitivity, the coarser the particles, and the coarser the enlarged photos will appear.

High-sensitivity film (above ISO400) is often used for window, indoor, night scene or stage photography. The lower the sensitivity, the finer the film particles and the better the texture, but the more light is needed, so it is necessary to have good light or use a tripod when shooting. Low-sensitivity film (below ISO 100) is suitable for portrait or landscape photography.

contrast

Contrast refers to the ratio of the brightness of the shot image to the brightness of the original scene. If the brightness of the subject is correctly reflected on the negative with film, we call it contrast1; If the negative number is greater than the subject, it is greater than 1.

Look at the picture and you will understand. The contrast of the photo gradually increases from left to right. Generally speaking, big contrast can shock people, but it will make it unreal. Contrast is not only related to the film itself, but also related to development.

Gray fog

Fog is the gray density produced by the unexposed development of film, which is reflected in the photo to make it too bright. The smaller the fog, the better. Fog is caused by the film itself, inaccurate exposure and improper development.

latitude

Tolerance refers to the ability of the film to represent all brightness intervals of the subject. Generally speaking, the latitude of the film is limited, less than the real scenery. Therefore, when shooting, the contrast of the scene is often too large. At this time, it is necessary to choose a range, a range to be expressed by movies.

Assuming that the scene has 200 levels from the darkest to the brightest, the film can only show 100 level. If you choose 1 ~ 100, then only one side of those scenes at 100 ~ 200 will be white, which means the layer is lost.

This is one thing, and one more thing. For color film, although it has great tolerance, it can express the level most correctly, and the range of colors is very small. This is the reason for accurate exposure. If it is half gear, the effect will be different.

maximum density

The highest density is the highest degree that the film can be black.

solve

Resolution refers to the ability of film to clearly distinguish the details of the subject. Simply put, it is the number of separable lines that can be expressed per unit area.

granularity

Particle size refers to the size of silver particles after exposure and development of ready-made film images. Note that this is different from the resolution. Although small granularity is good for resolution, just like two lines, although the lines are very thin, we can't tell them apart if the distance is very close and the colors between the lines are similar.

Sensibility

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.

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