Which EOS cameras can use split circle viewfinder screens?
Back in the 1960s and 70s microprism viewfinders were common in SLRs. These were special viewfinder screens containing tiny prisms on the surface. These prisms would break up the surface of out of focus areas, making it easier to focus. A later innovation was the split circle (split prism) viewfinder. Such viewfinder screens featured a circle, bisected by a usually horizontal line, in the centre of the screen. To focus the camera you would find a high-contrast vertical line (eg: edge of a wall, a tree trunk) and look at it through the viewfinder. You would then adjust the focus until the line appeared unbroken in the split circle. Split circles worked quite well, but had two notable drawbacks. First, you needed to find a straight line to focus on and second, the image in the circle tended to black out when used with very slow lenses. There were also combination viewfinders with split circles in the centre and a ring (collar) of microprisms. Sadly, most camera makers ditched these conve
