( شرح الجدولين رقم ٤١ ، ٤٢ ) ، مقياس النقل Reproduction scale .. كتاب المرشد العملي

Explanation of tables No. 41 and 42

Reproduction scale

The transmission scale is the ratio between, the length of the image on the negative film and the length of the object in nature

If the length of the image is equal to the length of the body, then the size of the transfer = 1: 1, and if the length of the image is less than the length of the body, then this is a case of imaging with magnification.

The degree of magnification depends on the following factors:

1- The focal length of the lens increases the magnification and the focal length of the lens shortens.

2- The distance between the image and the lens: the magnification increases as the image distance from the lens increases, i.e. the longer the bellows extension or the extension tubes length.

3- The distance between the body and the lens: the magnification increases whenever the distance of the body from the lens decreases.

Knowing the transmission scale is of great importance to the photographer in the conditions of close up photography or macrophotography, as accordingly it is possible to know the correct exposure, as we will see later. And the two tables No. 41 p. 84 and 42 p. 85 show us the measure of transmission if we know each of

(a) Focal length of the original lens
(b) The distance of the object from the lens

In one of them, No. 41, the distance of the body from the lens was estimated in inches, and in Table No. 42, the distance of the body from the lens was estimated in centimeters.

Example: What is the measure of transmission if the focal length of the camera lens = 6 inches (i.e. 15 cm), and the body is far from the lens = 45 cm?

Answer: From Table No. 42 on p. 85, we find that the transfer scale at that time = 2:1.