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 - -  - - - A Brief History of Nikon's Meter Coupling Systems - - - - - 

When the first meters for the Nikon F were introduced in the early 1960s, they used a "pin and yoke" arrangement for coupling the lens to the meter. This technique was simple and effective but required additional effort to "index" the combination. In 1977, Nikon came out with a line of cameras that retained their traditional lens mount but incorporated a new method for meter coupling. It consisted of a spring-loaded ring around the lens mount with a protruding tab that engaged the end of a corresponding recess in the aperture ring of the lens. This new system provided for proper meter coupling immediately upon mounting a lens. It was known as Automatic Indexing (AI). Here is an example.

The aperture rings on their new lenses continued to be equipped with the familiar coupling shoe in addition to the recessed section. These were known as AI lenses, and later AI-s. The new bodies, on the other hand, were not fully compatible with the old lenses since the metering tab could interfere with the aperture ring. Nikon addressed that problem by using a hinge on the metering tab that allowed the tab to drop out of the way.

To counter this inconvenience, Nikon instituted their AI Conversion service. For most of their more recent non-AI lenses, they replaced the existing aperture ring with a new one that was fitted with both AI and non-AI connections. Beginning with the E series lenses in 1979 and continuing through the Autofocus models of today, the familiar meter coupling shoe was no longer installed. The Nikon EM, also introduced in 1979, was the first body that had a fixed, rather than hinged, metering tab. That meant that older, unconverted lenses could not be used at all. Nikon discontinued their AI Conversion service in 1991 due to waning demand and a lack of parts. In Nikon's present product line, the F5 is sold with a fixed tab but a factory retrofit to a hinged one is available. All other bodies either have the fixed tab or couple by electronic connections only.

In 1987, the N4004 began a new line of bodies that relied on the microprocessor in the autofocus lenses to support their metering functions. The lens mount did not include a metering tab since all the connections were made electronically. The most recent models in this line are the N60, N65, N80 and the D100. The Fuji S1 and S2 digital bodies also fall in this category. Use of autofocus lenses on these bodies is recommended since ambient light cannot be measured when manual lenses are used. In addition, the conversion that allows old lenses to even be mounted requires additional work (and a $10 surcharge). To further compound the issue of compatibility, Nikon has recently begun to issue a line of lenses known as Series G. These lenses have no aperture ring at all. They will mount safely on all bodies but must be used wide open on models that have no electronic couplings.

Thus, there are now four distinct types of bodies and four distinct types of lenses. I have used the terms Old, Transitional, New and Electronic Coupling Only to describe them. The accompanying Compatibility Chart outlines their compatibility in general. A detailed table is also available as a .pdf (Portable Document Format) file that can be opened and printed with Acrobat Reader software available free from Adobe getacro.gif (712 bytes)

For real history buffs, here are two pages from Nikon's original (July, 1978) flyer on their conversion service. One is the description of their new service and the lens chart which listed all the lenses that they could convert. Both are .pdf files. Note that Nikon only converted lenses that were in certain ranges of serial numbers. That was because they manufactured new rings and chose not to make them for their oldest lenses. Because my conversions are done by machine work on the existing aperture ring, I can convert virtually any Nikon lens that couples to the older bodies.

I have also been collecting some links to Nikon-related sites.

For prices and shipping information, click here.


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