Depth of field and subject distance

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The depth of field therefore increases with increasing subject distance. The further away we place the camera from the subject, the larger the area in focus will be. Therefore, landscape photographs automatically have a larger depth of field compared to macros, due to the subjects being so far away. Mathematically, the formulas explain this just as in the case of aperture: A larger subject distance increases the denominator in the calculation of Dv and decreases it in the calculation of Dh. As a result, Dv decreases and Dh increases. Once again, Dh grows more than Dv, resulting in a disproportionate increase in the acceptable sharp area behind the focal point. Table 3 shows this clearly for a larger range of distances. At close distances, the ratio is 1:1, but as the distance increases, this distribution changes more and more in favor of the background. This occurs in exactly the same ratio as that between the far point and the near point. Therefore, the widely quoted distribution of the depth of field in the ratio 1/3 to 2/3 in front of or behind the focal plane is not a general distribution rule; it only applies if the distances are also in this ratio.

f/stop	Subject distance	Near point D1	Far point D2	Depth of field	Ratio
f/1,8	10 m	8,2 m	12,7 m	4,5 m	1:1,5
f/1,8	15 m	11,3 m	22,2 m	10,8 m	1:1,9
f/1,8	20 m	14,0 m	35,2 m	21,2 m	1:2,5
f/1,8	40 m	21,5 m	292,5 m	271,0 m	1:13,6

What happens becomes even clearer than the bare figures if we look at figure 29 (object width and depth of field) to see what happens to the ray paths with regard to the depth of field when the object width is increased.

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Main Visual acuity

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