About the principle of photogrammetry?

The camera rangefinder is used to measure the distance of the photographed scene, so as to focus the lens and achieve the purpose of clear imaging.

There are many rangefinders with different principles:

Rotating mirror type

It consists of a half lens and a rotatable mirror. When the light from the infinite object point can still see the coincident image point through the range finder, the mirror must rotate at a corresponding angle, and the distance between the scenes is different, so the distance can be measured by the rotation angle of the mirror.

Rotating prism type

The principle is the same as that of the rotating mirror.

Swing negative lens type

It consists of a semi-lens, a pendulum mirror and a mirror added to the inverse Galileo viewfinder. The distance from the pendulum mirror to the half lens is equal to the distance from the objective lens to the half lens. The pendulum mirror is fixed on the lever and swings around the center of curvature when working. The coincidence of double images of an object at a certain distance is determined by the angle of the pendulum mirror, so the distance is measured.

Moving negative lens type

The negative lens in the above picture does not swing, but moves back and forth in a straight line. Moving a certain distance is the coincidence of the double images of ranging.

I won't describe the others one by one.

The old rangefinder, ranging reading and lens adjustment are operated in two steps, which is inconvenient and rarely used. At present, camera ranging and focusing are linked, and two steps are completed at a time.