The Canon Ec-S Focusing Screen with Canon's exclusive Super Precision Matte technology makes it easy for professional photographers to determine the precise point of sharpest focus during manual focusing. This is because the microlens on the screen's matte is optimally shaped to increase defocusing near the point of focus.
Optimized for use with lenses whose maximum aperture is f/1.8 to f/2.8.
Reviews Canon Ec-S Focusing Screen for Canon EOS-1D Mark II N Digital Camera