Also known as a rangefinder, a viewfinder camera is a camera that creates an image that is completely separate from the image acquired through the lens, due to the viewfinder's offset from the lens. This problem in the camera is known as parallax, which occurs when there is a difference between what a camera shows you through the viewfinder and what the picture will actually look like. The viewfinder usually has its own simple lens which shows an approximation of the image that will be captured. Viewfinder cameras have a simpler construction and thus are easier to manufacture than single lens reflex cameras. The advantages of a viewfinder camera are that they are relatively inexpensive, have a less likelihood to break or malfunction (due to the simple construction), provide excellent focusing, and receive higher light levels.
How does a viewfinder camera work?
A rangefinder camera works the same way as a single lens reflex camera on the inside: light goes through the lens and forms an image on the film. However, the lenses are much smaller and do not have as many elements. The key difference between the rangefinder camera and the SLR is in the viewfinder. The viewfinder in a rangefinder camera has a separate lens, which means that you will see a slightly different image in the viewfinder than what is actually projected on the film. This error is called parallax, and can be corrected for.