Manual focus can be used with lenses that do not support autofocus (non-AF Nikkor lenses) or in situations in which autofocus will not produce the desired results.
Adjusting Focus in the Viewfinder
To use manual focus, turn the focus-mode selector (A) all the way to M and turn the lens focusing ring (B) until the image displayed on the clear matte field in the viewfinder is in focus. Photographs can be taken even when the in-focus indicator (●) does not appear in the viewfinder.
A 
B
Using the Electronic Range Finder
When a lens with a maximum aperture of f/5.6 or A faster is used in manual focus mode, the in-focus indicator (●) can be used to confirm focus in any of the five focus areas. With the focus-mode selector set to M, press the shutter-release button halfway. Before the focus indicator in the viewfinder disappears, rotate the lens focusing ring (A) until the in-focus indicator B (●) is displayed in the viewfinder (B). If the 
indicator is displayed, the camera is focused on a point between the camera and the subject. If the 
ndicator appears, the camera is focused on a point behind the subject.
For more information on:
pg. 80 Getting good results with autofocus pg. 73 Focus-area selection
