It is the exaggerated bright outline that we seek in focusing. With the Ricoh system, you get two ways of "peak" focusing, the first one comes with normal color but bright tiny dots that you should turn the lens barrel to make them as bright as possible. The second type makes everything appears in grey with bright edges. Turn the lens barrel to make the bright outline as bright as possible and you get the correct focus. Drawbacks - when you focus, you see a grey screen instead of colored one. But once you have finished focusing, half press the shutter and you get everything right back. Good part - the whole LCD screen will tell you patches of in focus and out focus as indicated by the brightness of the edges. When you turn your lens barrel, you can see exactly which part of the picture is in focused as compared to other parts. I was told that the Sony system is even better though it is of the same principle. I haven't tried. My personal experience is that the "peaking" system can be very fast and accurate, much more advanced than the traditional enlargement way of focusing with manual lens.