This Eg series Super Precision Matte Eg-S Interchangeable Focusing Screen from Canon provides easier manual focusing through your viewfinder on subjects in low light when using lenses with a wide aperture between f/1.8 to f/2.8.
This "S" type focusing screen works by decreasing the focus of the slightly out-of-focus areas around your in-focus subject for a sharper contrast.
Compatible with Canon EOS 5D Mk II and 6D
Not recommended for ordinary zoom lenses with maximum aperture slower than f/2.8 as the screen will appear dark and grainy
Focusing screens are delicate and should only be handled using the included gripping tool for installation