A definition of Viewfinder

A device which displays the scene being captured. This may be an optical type, which on a DSLR shows the image exiting the lens, or an electronic variety which simply displays the feed from an imaging sensor. Entry-level DSLR models are usually fitted with pentamirror viewfinders constructed from mirrors, while more expensive DSLRs are equipped with pentaprism viewfinders, which instead employ a glass prism. The latter variety produces a brighter image, although it's heavier and more expensive to manufacture.