In most of the Canon EOS, Nikon AF and Pentax AF cameras, whether digital or analog, electronic focus confirmation continues to be available even when using our ZE, ZF or ZK lenses. The camera confirms that the manual focus is correct by illuminating the focus confirmation light or the active AF point. In many of the Nikon models (e.g. the D700 and D3 series), additional support is provided by two arrows in the viewfinder which indicate the direction of rotation for the focus ring when performing fast manual focusing.
However, these electronic focusing aids only actually provide a relatively imprecise means of achieving high-precision manual focusing. The region shown as "in focus" when rotating the focus ring is generally quite large and is also dependent on the direction from which the subject is being brought into focus (i.e. whether you are coming from infinity or from the closest focus distance). We therefore recommend comprehensively testing the camera in combination with a manual lens in order to get a photographer's feel for the situations in which you can rely on the AF indicator. Especially when using fast lenses, it is advisable to take a bracketing series with a wide-open aperture and short shooting distances in order to achieve optimum results.