Aperture is the “pupil” of the lens, a hole of variable diameter. The narrower this diaphragm opening, the greater the depth of field – the depth of field. In modern cameras, you can choose intermediate values, for example, 3.5, 7.1, 13, etc.
The larger the f-number, the greater the depth of field. Large depth of field is relevant for landscape photography, when everything needs to be sharp – both foreground and background. Landscapes are usually shot at apertures of 8 or more.
The meaning of a small depth of field is to focus the viewer’s attention on the subject, and blur all the background objects. This technique is commonly used in portrait photography. To blur the background in a portrait, open the aperture to 2.8, 2, sometimes even up to 1.4. At this stage, we come to the understanding that the 18-55 mm whale lens limits our creative possibilities, since at a “portrait” focal length of 55 mm, the aperture cannot be opened wider than 5.6 – we begin to think about a fast aperture (for example, 50mm 1.4) in order to get a similar result:
Small depth of field is a great way to switch the viewer’s attention from the colorful background to the main subject.
To control aperture, you need to switch the control dial to aperture priority mode (AV or A). In this case, you indicate to the device with which aperture you want to take pictures, and it selects all the other parameters itself. Exposure compensation is also available in aperture priority mode.
Aperture has the opposite effect on exposure level – the larger the f-number, the darker the picture is (a pinched pupil lets in less light than an open one). This is compensated by a proportional increase in shutter speed.
If the aperture is closed too much, detail may be lost due to diffraction blur, but this is almost “higher mathematics” 🙂