How to use and control the light ratio to achieve the ideal shadow effect?

The light ratio is the ratio of the amount of light in the darkest part of the subject to the amount of light in the brightest part. The size of the light ratio directly affects the tone level and tone level of the picture, resulting in different modeling effects. To control the tone and correct exposure, the light ratio must be considered, such as the size of the light ratio, the similarity and difference of the light ratio, the meaning of the light ratio, the calculation of the light ratio, the adjustment of the light ratio, and the relationship between the light ratio and the tone.

There are three aspects to the light ratio of the scenery. First, the light ratio of the lowest brightness to the highest brightness of the scene range; second, the light ratio of adjacent objects with different reflectance; and third, the light ratio of the main light to the auxiliary light of the object with the same reflectance.

Planar objects are illuminated by light, and the brightness of each part is the same; three-dimensional objects are illuminated by light, there must be dark and bright parts; the light ratio of the same scene under high illumination conditions may be the same as the light ratio under low illumination conditions, but its connotations are different. For example, for lighting, 100 watts: 200 watts = 200 watts: 400 watts=1: 2. For another example, take the first piece of paper with half of 0 grade black and half V grade gray. The black and gray areas have the same illuminance, but the amount of reflected light is different. Take the second piece of paper with half V grade gray and half X grade white. The gray and white areas have the same illuminance, but the amount of reflected light is different. The light ratio of the first and the second may be the same, but their connotations are different.

Under normal sunlight, the average light ratio of ordinary scenes is about 1:160, the light ratio of black and white film is about 1:128, the light ratio of color negative film is about 1:64, and the light ratio of color reversal film is about 1:32. . The fundamental task of photography is to match the light ratio (latitude) of the imaging carrier with the light ratio of the subject. If the light ratio of the film is greater than the light ratio of the subject, then the exposure is fine; if the light ratio of the film is less than the light ratio of the subject, the bright parts must be overexposed and the dark parts underexposed. Outdoors, the solution is to darken the sky with a gray gradient lens, and the second is to exclude some bright or dark parts of the scene when composing the frame, thereby reducing the light ratio.

The light ratio directly affects the tone level and tone level of the picture. If the light in the darkest part is set to 1, the film can hold up to 1:1.1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:16, Light ratio range of 1:32 (the highest latitude of color reversal film), 1:64 (the highest latitude of color negative film), and 1:128 (the highest latitude of black and white panchromatic film).

For portraits, if the subject light ratio is 1:4, the contrast is moderate and the tonal levels are relatively richest. When shooting natural scenery or humanistic scenery, the light is ever-changing, and the light ratio is difficult to estimate. When the pre-sensitivity ratio is large, it should be measured to prevent the scene-to-light ratio from being larger than the film latitude and no measures are taken. If the light ratio is large, the photo has a large contrast between light and dark, and the tonal boundary is not obvious, and the three-dimensional effect is strong, but the details are not clear; if the light ratio is small, the photo has a small contrast between light and dark, the tonal boundary is not obvious, and the three-dimensional effect is weak, but the details are clear.

The main methods of calculating the light ratio are as follows: 1. When shooting with artificial light, use the lamp distance and wattage to calculate. If the lamp distance is the same, the auxiliary light is 100 watts, and the main light is 200 watts, the light ratio is 1:2, and so on. If the wattage is the same, the main light distance is 1 meter, and the secondary light distance is 2 meters or 3 meters, then the light ratio is 1:4 and 1:9, according to the "law of inverse illuminance" and analogy. Second, when shooting in natural light, use the shutter priority mode to set a speed (1/125 sec) first, under the premise of the same speed, use the spot metering mode to first spot the darkest part of the scene, if the aperture is F4, then Measure the brightest part of the bright part of the scene. If the aperture is F8, then the luminous flux of F8 is 1/4 of F4, and the light ratio of the scene is 1:4. And so on. These two methods are operable, but they are not very precise.

The relationship between light ratio and tone. Taking portraits as an example, a light ratio of 1:2--1:3 is suitable for soft-tone photos; a light ratio of about 1:4 is suitable for mid-tone photos, which can reproduce the details of the subject and has the widest application range. ; 1:5-1:6 light ratio, suitable for hard-tuned photos; 1:7 light ratio is suitable for half silhouette shooting; 1:8-1:9 is suitable for shooting silhouettes.