What are the aperture-priority shooting techniques for using a lens hood, and what should you keep in mind?

　　What are the aperture-priority shooting techniques for using a lens hood? It’s a “hot topic”—most people use it in most situations, yet they don’t necessarily master it.

　　1. Choose the aperture size based on depth of field. The primary function of the aperture is to control the amount of light entering the lens, much like how the diameter of a faucet regulates water flow. However, according to the principles of optical imaging, the aperture setting directly affects the depth of field in the image.

　　Indeed, the photographs we take are, at their core, merely two-dimensional; yet, in terms of the visual world they depict, that image actually possesses depth—this depth is what we call depth of field.

　　To put it another way, our image is essentially a cuboid: the side facing us is one face, while five other faces exist as well. If we define the edges of the face facing us as the length and width, then depth of field is simply the “height” of the cuboid—its magnitude corresponds to the size of the depth of field.

　　When composing a photograph, we must always consider the depth of field, which is controlled by the aperture: a wide aperture yields a shallow depth of field, while a narrow aperture produces a greater depth of field. We can use this principle to guide our compositional choices.

　　2. For image quality, choose a medium aperture. Most lenses have an aperture range of roughly f/2.8 to f/18; different lenses vary, with some offering wider maximum apertures like f/1.8 or f/1.4, and others narrower minimums. In Chinese culture, the principle of “the Doctrine of the Mean” emphasizes avoiding extremes—so in everyday shooting, there’s no need to push the aperture to its limits. As far as image quality is concerned, most lenses deliver their best results around f/5.6 to f/11.

　　Generally, when shooting wide landscapes, expansive scenes, or nightscapes, opt for a smaller aperture; for portraits of small groups or individual subjects, choose a larger aperture. Many photographers favor using a wide aperture to blur the background in portrait photography. However, even if a lens has a maximum aperture of f/1.8, shooting at that setting doesn’t always yield the best results. The ideal aperture is typically one to two stops smaller than the maximum—so don’t overuse either very wide or very narrow apertures.

　　3. Maintain overall control by learning to “make concessions.” The advantages of aperture priority are self‑evident, but sometimes, as the saying goes, “even good wine should not be drunk in excess.” For example, when shooting night scenes, you might set the aperture to f/18 to achieve a deep depth of field and, reportedly, capture starbursts from streetlights, while also choosing an ideal ISO setting like 200–400. However, as darkness grows and the exposure time displayed in the viewfinder begins to flash, it signals that, at your chosen aperture and ISO, the required shutter speed exceeds 30 seconds—far beyond what the camera can handle in this mode. At that point, someone has to step in and adjust one of the settings, making a “broad‑minded compromise.” If you lower the ISO, image noise will increase and image quality will suffer significantly. So who gives way? Only the aperture: slightly opening it up to extend the exposure time and resolve the issue.