The preview window on a camera that is used to frame, focus and take the picture. The viewfinder is an eye-sized window that requires the camera to be pressed against the face. All analog cameras have viewfinders but not all digitals have them. Professional photographers generally prefer a viewfinder because it helps them hold the camera steady and allows them to focus on framing the scene without distraction.
Types of Cameras
Many point-and-shoot cameras have only an LCD display for previewing the image. Prosumer and digital single lens reflex (DSLR) cameras have both the screen and a viewfinder, which can be an optical lens or a tiny microdisplay. The first DSLRs did not have a "live preview" and used the screen only to display images after they were taken. See DSLR
and parallax error
Viewfinder and LCD
This prosumer camera has both viewfinder and live preview screen. The viewfinder has two advantages. Since it is held against the face, it helps steady the camera and uses less battery if the screen is turned off.