I believe split prisms work best at fast apertures. With the movement towards lower cost DSLR's and lenses, typical apertures are slowing down. Your typical Reb

I believe split prisms work best at fast apertures. With the movement towards lower cost DSLR's and lenses, typical apertures are slowing down. Your typical Rebel might never see glass f/2.8 or faster. High end cameras like the 1D and 5D series have always had better focusing screens and several different replacement options available.