Pentaprism

pen·ta·prism [ˈpen(t)əˌprizəm]  noun 1. A five-sided prism with two mirrored surfaces giving a constant deviation of all rays of light through 90°, used primarily in the viewfinders of single-lens reflex (SLR) cameras.  This simple-yet-brilliant mechanism has been instrumental in my life for almost 30 years since I first picked up a camera. Up until I…