What's the Difference?...... sometimes   not what  people think!

NAI, AI, AI'd, AIS, When is AIS Better?

NAI (Non-AI) Lenses

Nikon made NON-AI (NAI) lenses 1959 to 1977.    What's interesting about this is that they didn't start out being called "Non-AI lenses."   They started out being called "Nikon F Lenses" since that was the only mount there was.   Later in 1977, Nikon introduced "AI" lenses, and their predecessors strangely started being described in terms of what  they were not.    Imagine what it must of been like when God invented blondes.  Good thing we're not calling them "Non-Brunettes."    Would "Non-Tall" be better than "Non-Short?"  Strange, huh?   

All NAI lenses share a metering prong to couple to the early Nikon F, F2, Nikkormat, and Nikkorex meters.  Two of the many early lens characteristics are focal length  markings in centimeters rather than MM and a solid stainless steel bayonet base rather than the five mounting screws later lenses used.   About 1973 lenses with rubber focusing mounts started to appear.   About 1975 multicoating started to appear, identifiable by its green color. 

Please note that in at least this collector's opinion, the Original Nikon F Lenses, as introduced with the Nikon F in 1959, belong to a special class all to themselves.   They have many small characteristics which were discontinued after a short time, and make for a fascinating part of Nikon collecting.   

NAI lenses can be recognized by their metering prong which couples to  Nikon's various NAI meters, and    only ONE row of F/stops, not a large row and a small row like the AI  and AIS lenses, and a even back edge of the lens -- without a ridge like the AI and AIS lenses.   The metering prong is the silver thing near the  f/5.6 marking .   It has a ridge in the center of it for the meter coupling pin.    All  NAI  cameras would give incorrect exposures if the photog forgot to correctly couple the meter.  

To complicate things more, some manual focus lenses are neither NAI, AI, or AIS, they have no meter coupling of any kind. Among these are the Medical and PC Nikkors, and various older longer than 400mm lenses.    I use the astoundingly creative terminology of "Non-Meter Coupled" to describe these lenses.   Other sources use various terms, including lumping them together with the NAI lenses. 

What cameras were designed for NAI lenses?  

• 1st generation NAI meters were the clip on selenium meters   for the Nikon F and the  Nikkorex F.   The F clip on only mounts on top of the standard meterless prism.    They are  NOT TTL (thru-the-lens) meters.

• 2nd generation NAI meters required the photog to manually set the lens' maximum aperture to the meter each time they changed lenses:   the Nikon Photomic, Photomic T,  Photomic TN and Nikkormat FT.    The original Photomic was not TTL.  All later meters were.

• 3rd and last generation of NAI meters had a semi-automatic indexing feature: the Nikon FTn, Nikkormat FTn, Nikkormat FT2,  Nikkormat EL,  Nikon F2 Photomic, F2 Photomic S, F2 Photomic SB.   The photog turned the aperture ring from one f/stop extreme to the complete the NAI lens meter coupling.     If you don't,  the meter will have the wrong  maximum f/stop information and you will get incorrect meter readings.    In practice this semi-automatic method is faster than bothering to set the f/stops on the meter, as required by earlier methods.  If you set the lenses to f/5.6 before you bayonet them on the camera, they will often mount easier. 

Some later Nikon bodies, the Nikon FM, FE, FT-3, F2A, F2AS, F3, and F4 (which also meter with AI or AIS lenses) were designed to use NAI lenses with stop down aperture metering.   NAI lenses can also be used directly on meterless Nikons:  the Nikon F w/prism, the Nikkorex F, the Nikkormat FS, and the Nikon F2 w/prism. 

Mounting NAI lenses on any  AF Nikons MAY damage the camera. Some of the VERY late NAI lenses are multi-coated, but MOST are not.   You can recognize Nikon's multi-coating by it's green color. 

AI Lenses

In 1977 Nikon introduced AI or AUTO INDEXING meter coupled  lenses. Changing AI lenses is much faster and  less error prone than NAI lenses because the AI ridge automatically meter   couples when the lens is mounted.   A  second small aperture row is for  ADR (Aperture Direct Readout) which gives f/stop finder information on some bodies.   MOST AI lenses have Nikon's green multi-coating.     Nikon  maintained backward compatibility to previous Nikons by continuing the metering prong on the AI (and AIS) lenses. The prongs now have cut-outs in them to help illuminate the f/stop markings for ADR.   The prongs were discontinued on AF lenses, but may be added.

AI lenses work on all 1977 and later manual focus Nikon bodies, as well as all but the low end AF SLRs.   Depending upon the body, metering patterns available with AI lenses include Matrix, Centerweighted, and Spot. Three AF bodies offer NO metering with manual lenses, the NOT recommended N4004(F401) N4004s, and N5005.

As a side note, Nikon's AI metering coupling looks suspiciously like Minolta's older metering coupling used for MC and MD lenses since the excellent Minolta SRT 101.

Starting in about 1975 more and more Nikon lenses were produced with multi-coating.  You can recognize this by the green colored lens coating.

AI'D Lenses

Nikon at one time offered a AI conversion for Nikon NON-AI in which a  new aperture ring was installed with the AI metering ridge and the double row of f/stops (for ADR)  and the new cutaway prong.    Converted, they would work perfectly with the newer AI cameras of the time.    Nikon converted  lenses should be referred to as AI'd, even though most people mistake them  for AI. 

Nikon AI'd lenses have NO IDENTIFYING markings. In order to spot them, you simply have to know the older lens barrel styles. AI'd lenses are often bought and sold as AI because it is difficult to tell the difference. A good tip off can be the lack of multi-coating. If that "AI" lens doesn't have the green color of Nikon's multi-coating, it's probably AI'd.

Nikon has discontinued AI conversions.     Original Nikon AI conversion rings are VERY hard to find today.    A few people still offer AI conversions.     Such conversions are called "AI'd" lenses.   Some do a great job, some are not so great. These conversions are easy to recognize because of the obvious machined groove at the back of the lens, and the lack of a Nikon style 2nd aperture row.   For a user, the AI conversion makes the lens a LOT more serviceable.   Be careful, however.   Having this done to an early Nikon F lens will greatly decrease it's value to the collector.

Another way to recognize AI'd Lenses is if they DON'T give you matrix metering on your FA or F4 like the AI or AIS lenses. Not many people noticed at the time, but AI lenses  have lugs built into the back of them to give the meter extra information. These lugs were not added with Nikon's AI conversion and are necessary for the matrix metering of the F4 or FA.

AI'd lenses SHOULD NOT be mounted on the Nikon 4004, 4004s or 5005. Due to the internal construction of these cameras,  NAI and AI'd  lenses may shear off internal meter contacts. Those cameras are Dogs anyway, UGH.  The later N50 and N60, along with the APS Pronea, also do not tolerate NAI lenses.

AIS Lenses: A Technological Dead End

In 1981 Nikon introduced their AIS (AUTO INDEXING SHUTTER) lenses even though no Nikon could use AIS features until the FA in 1983.  AIS lenses look a lot like AI lenses, but have their smallest F/stop marked in ORANGE.

AIS lenses also have 1) a little indentation in the stainless steel lens mount to indicate that a lens with a linear action diaphragm was mounted.  This feature was originally used on the FA/FG/2020/2000.    No current production Nikon camera uses this information.    2) internal modifications to allow AIS lenses faster and more accurate  shutter priority and programmed exposures by way of linear aperture movement, i.e. an equal mount of movement anywhere along the linkage results in the same amount of diaphragm action.

Construction-wise, AIS lenses are usually smaller and lighter than their predecessors. In other words, costing cutting was coming home to Nikon.   Most AIS lenses show cheapened construction.   The typical five screws for the bayonet mount was reduced in most cases to only three.   The traditional chrome ring on Nikon lenses between the focus ring and the aperture ring was replaced by aluminum.

IF the optical formula is the same--as they often are--I prefer the heavier constructed AI lenses over the AIS.

Is AIS Better than AI? Not often!

AIS lenses offer minor advantages on the Nikon FA,  2000, and 2020 ONLY, that's it!     On these THREE cameras, AIS lenses allow  use of the "HI" program exposure, giving  higher shutter speeds with lenses longer than 135 when the camera is set on PROGRAM.    THAT'S IT FOLKS. Whoopdedoo. The later AF cameras usually replaced this feature with a program shift.

The current lineup of Nikon AF bodies makes NO distinctions between AI , AIS, or AI'd lenses in terms of features or metering options (the F4 did, but it's discontinued).

Read it again, it's important: The current lineup of Nikon  AF bodies makes NO distinctions between AI , AIS, or AI'd lenses in terms of features or metering options(the F4 did, but it's discontinued).

Some claim that  AIS lenses are needed for program mode on the FA/FG/2020/2000.   I don't think so:  it's not what the instructions books say that I've read.    They all will work with AI in program.    Just set the lens to its smallest F stop and shoot.

If you plan to use manual lenses with current AF bodies, think twice before paying extra for AIS lenses.  They seldom offer any benefit!

Revised: November 25, 2003 .  Copyright � 1998-2002  Stephen Gandy. All rights reserved.    This means you may NOT copy and re-use the text or the pictures in ANY other internet or printed publication of ANY kind.  Information in this document is subject to change without notice.  Other products and companies referred to herein are trademarks or registered trademarks of their respective companies or mark holders.