Originally posted by jatrax The AF confirmation will confirm OK with anything within a range that roughly compares to a lens at f/4 or f/5.6.
Actually, on the K-3, the centre focus points are effectively f2.8, which is better than the stock focus screen can manage. In other words, using focus confirmation with one of the centre points selected makes sense on that camera.
Even with a properly shimmed replacement focus screen, such as the cut-down Canon Ee-S, focusing at f1.4 is largely a matter of skill (and luck).