How to create a contrast between light and shade

Because of the different angles and quantities, the light shining on the subject will definitely cause different dark contrast, and the photographer should also be able to use this light contrast to shape the outline of the subject and create the emotional atmosphere of the image.

Then, how should we control the contrast between the main light and the auxiliary light to get the contrast effect we want?

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Generally speaking, the exposure should be set according to the main light surface of the actor's face (of course, this rule is often broken by photography directors). The darkness of the auxiliary light side will affect the emotional tone of the image. Contrast can quantify the brightness difference between them.

The method to determine the contrast is to compare the light on the main light side (that is, the main light plus the auxiliary light) with the light on the shadow side (that is, the auxiliary light alone), that is:

Main lamp+auxiliary lamp: single auxiliary lamp

If the reading of main light and auxiliary light is 120FC, and the reading of single auxiliary light is 60FC, the contrast is 120: 60, that is, 2: 1. When the contrast ratio is 2∶ 1, the difference between the main light and the auxiliary light and the single auxiliary light is 1.

The contrast ratio of 2∶ 1 is relatively flat, which is a typical contrast ratio made by ordinary TV. It not only has modeling function, but also retains brightness and avoids obvious deep shadow.

If the difference is 2-stop aperture, that is, the contrast is 4∶ 1, the auxiliary light side will be obviously dark, and the contrast style between light and dark will be more dramatic. For most normal cases, the contrast is kept between 2∶ 1 and 4∶ 1.

When the difference is three steps, that is, the contrast is 9∶ 1, the auxiliary light side is almost completely black, and only some details are left in the shadow area.

When the sun shines, the contrast is usually 9∶ 1, so auxiliary light is needed to reduce the contrast.

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The film's latitude, also known as the exposure range, refers to the range of the weakest to strongest light that can be recorded by the film, which is calculated by the ratio of the minimum incident light to the maximum incident light.

For example, if the aperture is opened to f44, the light input is n, and then we increase the aperture by 10 step. When the aperture is set to f 1.4, the light input is 1024n, and the ratio between them is1:1024 ≈1:65438+.

Exposure latitude refers to the ratio of the maximum exposure of film without losing strong light details to the minimum exposure when obtaining shadow details.

This value represents the allowable variation range of camera exposure, often expressed as logarithm of exposure. In fact, it is also expressed by aperture, and the first aperture is equivalent to the logarithm of 0.3 of the exposure.

Exposure latitude is equal to the difference between the film width and the scene brightness range.

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Compared with film emulsion, the contrast range seen by human eyes is much wider.

When people watch a scene, they can see the details in every shadow and every bright spot. However, on the film, anything that is too dark or too bright will begin to become unclear as it approaches the two ends of the film relative to the selected exposure tolerance.

It is helpful to think about the hue in black and white pictures. There are a series of gray values between pure black and pure white, and the picture is expressed by various gray levels.

The purpose of choosing exposure and scene lighting is to make the gray value of the picture conform to the photographer's imagination.