عمق الميدان .. كتاب أسس التصوير الضوئي

Depth of Field

Depth of field is the ability to obtain sharp details over a large area. In order to bring this closer to understanding, we suppose that the lens of the camera is 200 cm away from the object being photographed. If the distance in the camera is set to: What distance from the lens is less than that?

(For example, 100 cm) or more than this dimension (for example: 300). (Noun) Are the details sharp? Share? Or is the detail not sharp?

If the accuracy of the details is limited to the distance of 200 cm only (which is the one on which the distance is set) or the area of ​​​​the fine details increases more or less than that by a few centimeters around this distance, then there is a decrease in the depth of field, but if the area where the details appear sharp is wider than that So much so, there is depth in the field.

Factors affecting depth of field.

(1) Diaphragm slot. The narrower the aperture of the diaphragm, the greater the depth of the field can be obtained. 3.5 We weigh between the two results, we find the following:

(a) f22 lens The area of ​​sharp details extends from the area with the lens 140 cm and ends at a distance of 380, for example, thus leading to a large depth of field.

(b) The f-3.5 lens extends the area of ​​sharp details from 190 by 210 only, for example, and it is understood from this that the wide diaphragm aperture reduces the depth of field, as shown in Figure 40.

(2) The focal length of the lens

The depth of field increases when using lenses with a short focal length when using lenses with a long focal length. Example: If we use two lenses in one camera, the first with a short focal length and the second with a long focal length, and the distance between the body and the lens in both cases is 200.

(For example, 4 f) We found when using a lens with a long focal length "that the area of ​​sharp details extends from 180 cm from the lens to 220 m, for example, while when using a lens with a short focal length, the sharp details extend in the image to an area starting 150 cm away from nothingness to 250 cm from the lens.

We conclude from this that the use of short focal length lenses helps in obtaining depth of field. For this reason, one must always take into account accuracy in adjusting the distance when using lenses with a long focal length, especially telephoto lenses

(3) The distance of the body from the camera:

Suppose we made two images in a row using one lens and a fixed aperture diaphragm.

The body is 150 cm away from the camera in the first picture D D 300 cm. Second, if we compare the result of the two images, we find the following

A) In the first case: objects that are 15 cm away from the body, for example, appear, whether from the front, back, or sides, with clear details:

b) In the second case: objects that are 60 cm away from this body, for example, appear, whether from the front, from the back, or from the sides, with clear details.

From the previous example, we can determine that the farther the camera is from the point.

The higher the distance, the greater the depth of field. This is with the previous factors remaining constant. In most cameras, there is an indication of the depth of field, and it is possible to know the amount of depth of field that can be obtained according to the aperture of the diaphragm used and the distance at which the lens is set. (Fig. 41)

It is understood from this statement (Fig. 41)

That if you set the diaphragm aperture to 8.2 f, the depth of field extends from 18 to 45 feet from the lens.
And that if you set the diaphragm aperture to 4 f, the depth of field is from 15 feet to 60 feet from the lens.
And that if you set the diaphragm aperture to 8 f, the depth of field extends from 135 feet to infinity.
And that if you set the aperture of the Dia, then set it to 11: f. The depth of field extends from 10 feet to infinity as well.