Lineage By Margaret Theme

Equalization in Depth of Field and Focus Distance

Para conocer cómo varía la Profundidad de Campo en función de la Distancia de Enfoque, deberemos basarnos en un par de cosas que ya conocemos, a saber:
a) El tamaño del círculo de confusión depends exclusively on the size of the sensor.
(See the article on the Circle of Confusion).
b) The thin lens equation can be expressed as q = pf / ((p - f).
where:
p is the distance from the objective focal plane.
f is the lens focal length.
q is the distance the image plane, corresponding to the focal plane, the target.
(See article on thin lenses.)
From the knowledge of these facts and taking the example of a normal lens 35 mm for the APS-C, we obtain the value of q for three different focal planes, one located at 100m (100000 mm), one located 10 m (10000 mm) and a third at 1 m (1000 mm) .
q1 = (100000. 35) / (100000 - 35) = 35.01
q2 = (10000. 35) / (10000 - 35) = 35.12
q3 = (1000. 35) / (1000-1935) = 36.27
" do these results mean? Well
focus levels between 100 m and 10 m are their images in a range of
35.12 - 35.01 = 0.11 mm.
and focus levels between 10 m and 1 m are their images in a range of
36.27 - 35.12 = 1.15 mm.
This means that the density of levels is much higher in the first interval in the second. Since, a constant aperture, double inverted cone to a point defined image plane for the circle of confusion is the same, within double inverted cone that are located many more flat image in the first case than in the second and, therefore, the depth of field is greater.
Therefore, we can establish the following rule:
a) If the focus distance increases, the depth of field.
b) If the distance decreases Focus decreasing the depth of field.
This is why the very small depth of field found in the field of photography.