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The role of the aperture in a camera

Release Date:

2021-06-30 10:09

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　　1. Blur the background

　　In addition to adjusting shutter speed, the aperture also allows you to control depth of field.

　　Depth of field: In front of the lens—both before and after the plane of focus—there exists a certain spatial range. When an object lies within this range, its image on the film falls precisely between two circles of confusion, one at the front and one at the rear of the focal plane. The length of this spatial range is what we call the depth of field. In other words, within this range, the degree of blur in the image projected onto the film remains within the limits defined by the acceptable circle of confusion; and the length of this range is the depth of field.

　　Simply put, the shallower the depth of field, the more pronounced the background blur; the deeper the depth of field, the sharper the background.

　　At the same focal length, the larger the aperture—meaning the smaller the f-number—the more pronounced the background blur and the shallower the depth of field. Therefore, if you want to capture photos with a strong background blur, you should use the widest possible aperture at that focal length.

　　2. Adjust the shutter speed

　　Generally speaking, at a given ISO setting, a camera’s exposure is determined by the aperture size (the f‑number) and the shutter speed. As we learned in the previous article, the f‑number equals the lens’s focal length divided by the effective diameter of the aperture; in other words, the smaller the f‑number, the larger the aperture opening, and the more light that enters. Therefore, we can increase the shutter speed by opening up the aperture, or slow down the shutter speed by stopping down the aperture.

　　Lenses with large apertures typically deliver excellent performance in low-light conditions. In the DSLR world, a series of lenses known as “night lenses”—such as Nikon’s Noct 58mm/F1.2 and Leica’s NOCTILUX-M 50mm/F0.95 ASPH—feature exceptionally wide maximum apertures.

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