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This photo of the Ohio Club, in downtown Hot Springs, was shot using my old and trusty Nikkor 20mm f2.8 AI non-cpu manual-focus lens on a D800. It produced a beautiful color image with no barrel distortion or vignetting. This 20mm lens series is considered by many to be one of the best lenses Nikon produced. However, those that have only been in photography for a few years tend to over look these older AI (Auto Indexing), AIs manual focus prime (Non-Zoom) lenses when considering a lens purchase. There are many great values out there to be had.
Grant you, the budget level Nikon DSLRs are not equipped to handle these lenses, the D3000 – D5000 series cameras to name a few. To use AI lenses your camera will need the AI Tab, these cameras will also have the older style Auto Focus Pin, see photo on left below.
There is also a menu item to enter your non-cpu lens info.
It tells the camera what the focal length is and it’s maximum aperture. This info is then conveyed to various camera functions.
Non-cpu lens do not have the contact pins as pictured below.