This is the Cavision MHE52 viewfinder, a single lens element cap designed to mount over a 3.5 inch LCD, such as the 5D MkII, transforming the LCD into a viewfinder for Liveview and video work. It greatly enhances working in sunlight or conditions where the viewfinder can be hard to visualize allowing more accurate composition and focusing.
The camera mounts to the plate in front of the viewfinder which is adjustable to mount snugly to the LCD on most cameras. The double handgrip allows you to hold the camera steady while filming.
Please Note Height alignment of the LCD Viewfinder is intended for the Canon 5D Mark II and may not align properly with other cameras. For use with the Canon 7D and Rebel T2i an additional RPC4580 spacer plate must be requested.