Nikon Df review – Old F-mount lenses
Nikon has been keen to promote the fact that the Df can be used with the vast majority of Nikkor F-mount lenses, including pre-Ai versions. ‘Ai’ stands for ‘auto indexing’, and Ai lenses have a notch on the rear of the lens that rests against a sprung indexing post around the edge of some Nikon F-mount cameras.
The notch on the rear of the lens pushes against the post, which communicates to the camera the current aperture that the lens is set to. This has now largely been replaced with electronic communication between modern cameras and lenses, but for older manual-focus lenses it allows the camera to know the aperture of the lens being used so the camera can meter correctly.
Cameras lower in the Nikon range than the D7000 don’t have the auto indexing post, so older manual-focus lenses can only be used in manual-exposure mode. However, with no auto-indexing post, these entry-level DSLR cameras do have an advantage. Without the Ai cutaway, the rear of
pre-Ai lenses can cause damage to cameras that have an auto-indexing post as the post can get bent or become jammed when trying to mount a pre-Ai lens. Nikon had a service to convert pre-Ai lenses by simply replacing the aperture ring with one that featured the Ai cutaway, and many users actually made the conversion themselves by filing down the aperture ring. Doing this enabled the lenses to be used on Ai cameras.
There are still many unconverted pre-Ai lenses around, and their use is limited to entry-level Nikon DSLRs or older film SLRs.
Nikon has come up with a simple solution for this problem in the Nikon Df – the auto-indexing post on the camera can be folded down out of the way so it won’t be damaged by pre-Ai optics.
