While the AF on modern DSLRs is pretty darn good these days, there are times that you still may want to manual focus. With current standard focusing screens, it can be tough to achieve good manual focus. This is one of the advantages of rangefinder cameras. I recently replaced the focusing screen on my DSLR with one from Katz Eye. I like having a split prism focusing screen (one of the things I miss from my early film days when I was just starting to take pictures). While most of the time I am happy with AF, there are times I rely on MF (especially with macro or when shooting primes that don't support AF). Having a split prism focusing screen is an aid when relying on visual cues and/or the viewfinder focus indicator. The installation was extremely easy. Took 5 to 10 min total. They have online tutorials that walk you through each step. It has no effect on basic camera functions (metering, AF performance, etc.). It basically just adds a split prism to the central portion of your viewfinder image. The company also offers the option of adding grid lines (for example "rule of thirds" lines) if you so wish. Just throwing this out there in case it might be useful for anyone.