ضبط المسافة في آلة التصوير .. كتاب أسس التصوير الضوئي

First _ adjust the distance in the camera:

The distance in the camera is set in one of the ways referred to in (Fig. 7) according to the type of camera. The colloquial expression “setting the distance” is determined by a permanent relationship between:

a) The distance between the body and the lens.
b) The lens and the image.
c) The focal length of the imaging lens

The closer the distance between the object and the lens, the greater the distance between the lens and the image. What is meant by adjusting the distance in the camera is to move the camera lens forward and backward in a way that suits the distance between the body and the lens, until the image of the object falls on the sensitive plate or film in the camera, and the image comes out with sharp details completely.

All cameras are designed so that their lens can be moved forward or backward
To adjust the distance - with the exception of some primitive types such as the box camera, where it depends on the narrow aperture of the lens diaphragm, which reduces the appearance of the potential error when the distance is not set accurately.
But we define the relationship between the object's distance from the lens, and the image's distance from: the lens, i.e. the relationship between (x, y). We show the following: The two triangles (hdb) are similar to the triangle (and mb).

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​ ​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​If we observe the rules of negative and positive signs that determine that dimensions are considered positive if they are measured from the lens in a direction opposite to the path of the incident rays, and that they are considered "negative" if they are measured from the lens in the same direction as the path of the incident rays. According to this rule, we can decide the following: The distance (r) is considered negative, as it was measured from the lens in the same direction of the incident rays, e (x), as positive in a direction opposite to the path of the incident rays:
(p) and negative as it was measured from the lens in the same direction as the incident rays