ما هي النقطة المتوسطة التى يجب أن تضبط عليها المسافة . كتاب آلة التصوير

What is the middle point to which the distance must be set, and what is the appropriate f-number to achieve the required depth of field?

Suppose you want to photograph a place so that a certain group of objects appears sharp in detail, so what is the middle point that you must adjust the distance to and what is the appropriate focal number in order to achieve the required depth of field? These are the two questions that always come to mind of the photographer.

In response, we say that there are two ways:

(A) There is around the lens (in most still cameras) the Depth of Field Scale (Fig. 113, p.

(b) If this division does not exist around the lens or in the machine (and this often happens in cinematographic cameras), then this can be done according to what we explain in the following:

First - knowledge after the middle point:

The distance of the middle point = 2 x the distance of the nearest point X the distance of the farthest point the distance of the nearest point + the distance of the farthest point

That is, x = 2 x s x b over s + b

Depth of Field Scale

Most cameras have a way of knowing the depth of field based on our knowledge of both the f-number and the center point at which the distance is set. For example, it is understood from the figure above that the lens has been set at a distance of 10 feet (the white numbers) and a focal number of 48 (the black numbers written in Arabic in the inner white circle). Thus, the depth of field can be read (from the black numbers written in Arabic in the outer circle). As shown in the figure, the depth of field extends from 7.5 feet to 15 feet - the distance between 7.5 and 10 feet is the front depth, while the distance between 10 and 15 feet is the rear depth.

Example 1:

If I want to photograph an outside scene (on a street, for example) so that the required depth of field starts at 4 meters from the lens, and ends at 10 meters, for example, what is the middle point that the lens should be set at?

the answer :

After the middle point = 2 x 4 x 10 over 4 + 10 = 2 x 40 over 14 = 5.7 metres.

Example 2:

I wanted to photograph a specific place so that there is a depth of field that starts from 20 feet to 180 feet, so what is the point at which you set the distance?

the answer :

After the middle point = 2 x 20 x 180 by 20 + 180 = 2 x 20 x 180 by 200 = 36 feet.

Note: In (pg. 216) tables to know the middle point if we specify both the far point and the near point.