A subpage of #3 in this background brief
On hundreds of millions of smartphones the camera’s aperture cannot be changed by the user,
yet the user sees on the device’s screen a slider that previews the amount of blur that will be added to the photograph after the exposure—
— using an “aperture” scale marked off with various “apertures,” e.g., from f/1.4 to f/16.
The same on-screen “aperture” scale is used after the exposure to increase or decrease the amount of blur added to the photo after it was recorded.