Consulting photography technology

The metering system of digital camera generally measures the brightness of the reflected light of the subject, which is also called reflection metering. According to the different placement positions of metering elements, metering methods can generally be divided into external metering and internal metering.

(l) External metering: In the external metering mode, the optical paths of the metering element and the lens are independent. This metering method is widely used in head-up viewfinder shutter cameras with sufficient sensitivity and accuracy. Single-lens reflex cameras generally do not use this metering method.

(2) Internal metering: This metering method is based on the lens and is called TTL metering, which is consistent with the shooting conditions and can be automatically corrected when changing the phase lens, changing the shooting distance or adding a color filter. At present, almost all single-lens reflex cameras adopt this metering method.

In a single-lens reflex camera, there are two main schemes for placing metering elements: one is placed near the eyepiece in the framing light path, as shown in Figures A, B and C, which is called TTL universal metering; Second, it is placed in the photographic light path, and the light is reflected from the auxiliary mirror or the blade surface of the film plane and focal plane shutter to the metering element for metering, as shown in D and E in the figure. This measurement method is called TTL direct measurement.

At present, the metering methods used by cameras mainly include point metering, center metering, center key average metering, average metering mode, multi-zone metering and so on according to the different areas measured by metering elements within the shooting range.

Spot metering mode: the metering element only measures a small range in the center of the picture. When shooting, the camera lens is aimed at various parts of the subject many times and its brightness is measured one by one. Finally, the photographer determines the exposure parameters according to the measured data.

Central part metering mode: This mode measures the central area of the picture, accounting for about 12% of the picture.

Central focus average metering mode: This mode takes the center of the picture (about 60% of the picture) as the focus, taking into account the edge of the picture. It can greatly reduce the phenomenon of poor picture exposure and is the main metering method of SLR cameras at present.

Average metering mode: measures the average brightness of the whole picture, which is suitable for the situation that the light intensity of the picture is not much different.

Multi-area metering mode: the picture is metered by independent metering elements in different areas, and the data is processed by the microprocessor inside the camera to obtain appropriate exposure with high exposure accuracy. Backlight photography or when the contrast of the scene is large, appropriate exposure can be obtained without manual correction. Reasonable, get appropriate exposure and high exposure accuracy. Proper exposure can be obtained when backlight photography or scene contrast is large, and manual correction is not needed.