How do digital cameras use cumulative photometry to shoot large contrast scenes?

The method of using two readings introduced by us is called exposure setting cumulative photometric reading method, that is, one is photometric reading in shadow area and the other is photometric reading in strong light area. Let's further discuss and review some practical problems to guide the specific shooting.

When to use cumulative photometry

This method is only needed when the brightness range of the scene we want to record is wide. In other words, we only need to use this method when shooting scenes in Gao Fancha. Usually, this means that we only need to shoot in a bright sunny scene and the important part of the subject is in the shadow area, so we need to use this cumulative exposure method. Generally speaking, we don't have to use this method when the scene we shoot is cloudy or completely in shadow. These scenes generally have a low contrast range between the shadow area and the bright area, and most movies can easily handle this contrast scene within the tolerance range. In this case, we usually measure the most important part of the subject and shoot according to this reading. Shaded areas and bright areas are usually within the tolerance range of the film.

How to expose backlight

The most common scenes in Gao Fancha are bright skies or outdoor photos facing the sun. Backlight is the situation that light shines from the back of the subject, so that the best exposure can record the facial details of the subject if facing the silhouette of the camera.

When we face similar scenes, the first thing to consider is whether the details of the bright sky behind the subject are important. Maybe they're not important. In this case, we can simply measure the light at close range according to the face of the subject and shoot according to this reading. As long as we want to record the details of the bright sky, we don't have to bother to use cumulative photometry.

Another way to solve the exposure problem of Gao Fancha scene is to fill the shadow area with light. Professional photographers often do this. For example, the model is backlit by the sky, so its face is in the shadow area. Professionals usually use the method of projecting auxiliary light on the model's face to reduce the contrast range between the face and the background. How to do it specifically? We will introduce it in detail in the process of lighting, and here are only a few basic techniques: one is to use an auxiliary flash, that is, to project extra light onto her face with a flash. Another way is to use a reflector to reflect light to her face. The result is the same. Adding auxiliary light to her face narrows the contrast range between the model's face and the strong light area, so that the film can take care of both (strong light area and shadow area).

Boundary exposure

As we have said, when shooting Gao Fancha scenes with black and white film, we should focus on the shadow area, and the underexposure of the second aperture is usually safe. "Safety" is certainly not perfect. 1 aperture will be safer. Therefore, in the face of Gao Fancha scenery, we suggest using the boundary exposure method to shoot. That is, measure the light in the shadow area, and then shrink 2 apertures and 1 aperture to shoot. Film is very cheap. I would rather waste a film than lose an irreplaceable image.

When using an automatic exposure camera with a backlight button, if we are in doubt about whether to use this button, then we can take two photos respectively, one with a backlight button and the other without a backlight button.

color film

Note that our statement just now is valid for all negative films, including black and white and color. If color negative film is used, just like black and white film, the film is more tolerant of overexposure than overexposure and underexposure.

But what should we do if we use color reversal film? If so, the situation is just the opposite, and the tolerance of film underexposure is greater than overexposure. This is just the opposite of the tolerance of black-and-white film or color negative. So how should the color film be exposed? We will discuss this problem later. First, let's look at the other two parts.