Some cameras have a function to preview the depth of field. To understand how it works, you first need to know what the depth of field is, for example, you can read about it here.
Modern cameras always perform focusing at the maximum aperture. For example, if a standard 18-55mm F / 3.5-5.6 lens is used, then focusing will always be done on apertures from F / 3.5 to F / 5.6 (depending on the focal length). Continue reading