What does photometry mean?

Photometry refers to measuring the brightness of light reflected by an object, also called reflection photometry. According to the different placement positions of metering elements, metering methods can generally be divided into external metering and internal metering. In the external metering mode, the optical path of the metering element and the lens is independent, and internal metering is carried out through the lens.

In film and television, the lens has two fingers, one refers to the optical components used by film cameras and projectors to produce images, the other refers to the continuous picture taken from power on to power off, or the fragment between two editing points, also known as the lens. One finger and two fingers are two completely different concepts. In order to distinguish, one refers to the optical lens and the other refers to the lens picture.