Hyperfocal: How to get a sharp image with largest aperture?

Version en français : Hyperfocale : Comment obtenir une image nette avec la plus grande ouverture compatible ?

Capturing an image with a desired depth of field that extends from the foreground to the distant horizon can be a challenging task. However, by understanding the concept of hyperfocal distance, one can determine the optimal aperture and focusing distance for achieving sharpness throughout the entire scene.

1. Optimal aperture and focus distance for foreground-to-infinity sharpness

In this scenario, the goal is to have sharpness from the foreground to infinity. To determine the optimal aperture value, denoted as N, one can calculate the hyperfocal distance (H) using the formula H = f² / (c * N). Here, f represents the focal length, c denotes the circle of confusion, and N signifies the aperture.

To achieve sharpness from the foreground to infinity, the hyperfocal distance should be twice the distance to the foreground (FSP). Therefore, the formula becomes N = f² / (c * 2 * FSP).

For example, let's consider an APS-C sensor with a circle of confusion of 0.02 mm and a 23mm lens. If the foreground is at a distance of 3m, the focus distance should be set to 6m, and the optimal aperture (N) would be calculated as 4.41 f-stops.

2. Optimal aperture and focus distance for sharpness between a foreground and a background

In this case, the objective is to have intermediate sharpness between the foreground and the background. This scenario involves two unknowns: the aperture and the focus distance. The first plane of sharpness (FSP) can be determined using the formula FSP = H * D / (H + D), where H represents the hyperfocal distance, and D signifies the focusing distance. The last plane of sharpness (LSP) can then be calculated using the formula LSP = H * D / (H - D).

To find the optimal aperture and focus distance, the following formulas can be used:

- D = 2 * FSP * LSP / (LSP + FSP)

- H = 2 * FSP * LSP / (LSP - FSP)

Once the hyperfocal distance (H) is calculated, the aperture value (N) can be determined using the same formula as in the previous example: N = f² / (c * 2 * FSP).

For example, with an APS-C sensor, a circle of confusion of 0.02 mm, a 23mm lens, a foreground distance of 3m, and a background distance of 6m, the focus distance should be set to 4m, the hyperfocal distance (H) would be 12m, and the optimal aperture (N) would be 2.21 f-stops.

By understanding and applying these formulas, photographers can determine the optimal aperture and focus distance to achieve the desired depth of field and sharpness in their images. It is worth noting that the calculations may vary depending on the specific camera settings, sensor size, circle of confusion, and lens used.

Notes

The formula used are not applicable for macro photography which is a much more complicated domain.

[1] At hyperfocal focusing, sharpness is assured between a foreground located at half the hyperfocal* and the background located at infinity.

[2] 6m = 2 x 3m

[3] 4.41 = (23mm x 23mm) / (0.02mm x 2 x 3000mm)

[4] By the way, for H = D, these two formula give FSP = H / 2 and LSP = infinity, which was our previous case.

[5] 4m = 2 * 3m * 6m /(6m + 3m)

[6] 12 m = 2 * 3m * 6m /(6m - 3m)

[7] 2.21 > 2.204167 = (23mm x 23mm) / (0.02mm x 12000mm)