How to use Nikon IX Nikkor APS lenses on digital cameras
Nikon used to produce Pronea SLR cameras using APS film, and a matching range of IX-Nikkor interchangeable lenses. While the cameras used the standard Nikon AF G lens mount, the IX lenses were designed to be especially compact and lightweight to suit the camera bodies. One of the ways they achieved this was to have a reduced back focus, and the rear of the lenses protruded further than usual inside the camera's mount. The lenses available included 20-60mm, 24-70mm, 30-60mm and 60-180mm zooms.

Unfortunately the IX lenses are incompatible with Nikon 35mm, AF or digital camera bodies, as the rear protrusion prevents them mounting. There are some reports on the web (which Google will find) that the lenses can be modified by cutting off part of the extended plastic mount at the rear of the lens, but this seems a little drastic. The only DSLR that will accept Nikkor IX lenses without modification is the Kodak DCS 315, which was based on the Pronea 6i/600i body.

However, there's now an alternative approach which requires no damage to the lens, no technical skill and allows these lenses to be used on some modern digital compact system cameras. These have a very short register (distance from the lens mount to the image sensor), and many adapters are available for other lenses. Some of the more recent Nikon adapters have an aperture ring designed to allow the operation of the diaphragm on Nikkor G lenses and other types that have no manual ring of their own. Although we're sure this wasn't an intentional part of their design, some of these adapters happily accept the Nikkor IX lenses as well, as there's room inside the adapter to accommodate the protruding rear mount.

We've successfully used all four of the IX Nikkor lenses on our Panasonic G1 and GH1 using a Nikon G to Micro Four Thirds adapter. As with all such adapters the operation of the lens is fully manual. Focusing is simple using the camera's EVF or LCD, and exposure works fine in aperture priority auto and manual modes. As there's no aperture ring on the lens, the one on the adapter is used to stop the lens down if required.

The lenses may also work with Nikon G adapters for other mirrorless cameras such as the Canon EOS M, Fujifilm X, Nikon 1, Samsung NX (but see below) and Pentax Q, but please double-check compatibility with the suppliers of these adapters before purchase. We've tried all four IX lenses on a Nikon G to Sony NEX adapter, and they fit and work fine.

Added 14 June 2010
Updated 05 July 2010
Updated 13 March 2011
Updated 27 October 2011
Updated 24 November 2011

Can they be used on DSLRs?  
We received an enquiry asking about using these lenses on Canon EOS digital SLRs, but unfortunately we're not aware of any way to use unmodified Nikkor-IX lenses on modern DSLR cameras. The reason they can be used on some digital compact system cameras is that these are much thinner than SLRs, and the protruding part of the lens's rear mount is contained within the adapter. On EOS cameras the mirror gets in the way so the lens can't be mounted, even with an adapter. We thought that the lenses might be usable in Live View mode (where the mirror is locked up), but unfortunately our tests show that the rear part of an IX Nikkor lens fouls the sides of the mirror box and still won't fit.

There are ways to modify the protruding parts at the rear of these lenses, but these all seem to involve cutting the plastic, so aren't for the faint hearted... a Google search for MODIFY IX NIKKOR will find many references to the procedure.

Updated 18 November 2012

Samsung NX adapter not compatible
Not all adapters for Nikon G lenses to digital compact system cameras are suitable for IX-Nikkor lenses. The Nikon G to Samsung NX (NG-NX) adapter shown below won't fit, as the extended shroud around the electrical contacts on the rear of the lens fouls on the diaphragm control mechanism inside the adapter. 

Updated 17 January 2015