العدسة والحدقة - ٢ - طريقة عمل آلة التصوير .. كتاب التصوير الضوئي

Lens and pupil - 2 - How the camera works .. Book of photography

Depth of field

The distance between the nearest plane and the most distant plane of a three-dimensional subject, which is explained somewhat clearly, is called the depth of field. In other words, if we change the instrument to a subject located in the middle of the distance, for example - and if the first plane is also clear, then all objects located between these two planes will be clear: the image will have a large depth of field. Knowing that the depth of field increases the further the calibration distance from the instrument is, it is preferable - especially the subject that is close - to increase the depth of field by closing the pupil. A picture taken at 22/F will have a much greater depth of field than a picture taken at 4/F, but as a result the time taken to capture the image must be increased to give an exposure equal to the film.

Useful note: Except for very close subjects, remember that the depth of field is one-third at the beginning of the surface on which the calibration was made and two-thirds at the end. Most instruments and lenses are equipped with a depth of field scale. As we mentioned earlier, depth of field should not be confused with focal depth. The term (depth of field) means the boundaries between two planes perpendicular to the theoretical axis, translating objects between them in a way that can be considered clear. The laws that determine the importance of the field apply to all lenses, but it can be increased or decreased by playing with the focal length, for example. Therefore, lenses with a short focal distance give a greater depth of field than lenses with long focal distances. However, the depth of field is the same for the same magnification and the same aperture.

How to exploit depth of field:

It is often possible to show one plane of the subject (top left image) while leaving the other planes blurred. We get a more detailed image (center image) by narrowing the aperture of the aperture - and if we close it more (bottom image), we can extend the clarity to the entire subject.

The lens is set at 3 meters and the aperture is set at 2/F. The very specific depth of field is not indicated on the scale.

At the same focal length but with an increase in the aperture to 8/F, the depth of field scale indicates that it extends from 2.10 to 4.50 meters.

When the aperture is at 16/F and the aperture is at 3 meters, the depth of field extends from 1.5 to 9 meters.

Changing the aperture: When the aperture is increased, the aperture becomes smaller: A wider and more spacious depth of field is proportional to something in which the aperture is increased. That is, an aperture of 16/F has a greater depth of field than an aperture of 2/F.

Changing the lens-subject distance The depth of field decreases the closer we get to the subject. That is, it is greater for a 4.5 meter than a 1.5 meter.

Changing the field distance The depth of field extends the shorter the focal length. With the same aperture and the same caliber. 28 mm gives a depth of field of more than 135 mm.