Install KatzEye Focusing Screen in Nikon D300
Focussing manually has it's advantages. First, the number of potential lenses for your body sky-rockets. There are numerous old and new extraordinary good MANUAL FOCUS lenses available for the modern DSLR. Examples are lenses by Voigtlander, Carl Zeiss, and the old Nikon (Ai-S) lenses. The problem is that most of the modern cameras lack a decent (visual) indicator for when your object is in focus. My Nikon D300 has a small indicator (a dot) in the viewfinder which notifies you when you've got focus. But when you shoot with large apertures (e.g. f/2, f/1.8, f/1.4 or f/1.2) on MF lenses you have to keep track of your composition (through the viewfinder), and watch the 'in-focus' indicator. Something I find very hard to do. I allways seem to miss at least one of them. Missing composition is easy to fix in post-processing, but fixing focus can't be done.
Thankfully, there's a solution to this problem; Katz Eye Optics. These guys offer old-skool focusing screens for the modern digital SLR's. All you have to do is replace the focusing screen with theirs. You can do this yourself, or your camera brand service-center should be able to do it for you (at additional cost). I did it myself though, and ran into a problem (of course). But more on that later...