Non AI lens.jpg (15k) AI Converted Nikkor.jpg (15k)
A Non-AI Nikkor lens

Note: the rabbit ear is a solid piece in an original non-AI lens.

MANUAL FOCUS Nikkor Resources | Autofocus Nikkor Resources

But most important part is the lack of the meter coupling ridge that may lead to very few options in the metering capabilities in Nikon bodies after 1977/78.

These lenses works fine on non-AI bodies. But when you intend to mount such lens on a Nikon body that doesn't have a meter coupling lever that can be released or raised (By way of the meter coupling lever release button), only stopped down metering is permissible on such cameras.

An AI-modified Nikkor lens
*"Ai" stands for: (Automatic Maximum Aperture Indexing). It is in fact the same 105mm f2.5 Auto Nikkor used for the illustration earlier on the Nikkormat FT2. Modification is by changing the aperture ring, it will come as an AI lens, the meter coupling shoe will have rabbit ears that have holes in them.

<<<-- Lens mount of Nikon F2AS w/metered Prism DP-12. it is the FINDER section that enables the Ai, NOT th lens mount.

The meter coupling shoe will allow lenses to couple for proper indexing on non-AI bodies. This lens was modified by a serviceman outside Nikon service centre, as evidenced by the screws used. The aperture ring may have been changed, but you can notice even if the lens has been modified (basically just changed the aperture ring), it cannot substitute other parts such as the lens speed indexing post (lug) behind the mount .

AI lens.jpg (15k) AI lens Illus.jpg (7k)

* More info and illustrations..
The lack of such features in an AI-modified lens is the reason why such lens CANNOT perform matrix metering on cameras like FA or F4, as is the case with AI or AI-S lens. You must have noted since this is the AI-modified lens, that the aperture ring has another 'stopper' for the meter coupling lever. Some accessories like the AI- DS-12 EE Aperture Control for the Nikon F2AS need this in order to offer automatic AE operation.

An original AI lens

Spotted any differences from an AI converted lens? It is difficult. But AI lens has an additional lug to provide additional info for metering. (Note the above Non-AI and AI modified lens has no such lug(s).) It can also work in programmed mode (Shutter Priority AE for FA) in the FA or FG. The matrix metering in the FA or, even in the Nikon F4, etc., works perfectly stable. (But not on shutter priority and high speed programs as in the case of the F4, because data exchange in the F4 is electronic, while the FA is mechanical). This Nikkor 50mm f1.4 lens illustrated above has three screws on its back, while longer focal length lenses, the AI model will have five screws (as with the earlier Non-AI lenses) for steadier support. Generally, AI lenses exhibit first rate build quality, the mounting ring is made of chrome metal. Rigid and solidly built throughout - like the lens mounting ring, it is a solid mat chrome band with a milled surface for firm grip when changing lenses: this was changed to aluminum in the AI-S.

AIS lens.jpg (14k)

AI-S lenses generally has only three screws to secure the back portion. However, longer and bulkier lenses are fitted with five screws for support.

An Ai-S lens is best recognized by its lens type signal notch - the little milled notch next to the lens locking indentation. This indicates that the aperture stop down action is linear as opposed to pre-AI-S lenses. An AI-S lens also has another feature; it can tell the camera* its focal length on a very crude scale; below 135 or above or equaling 135 mm.

*FA, F-501 & Nikon F4; ** FA & F-501

This is done via the so called focal length indexing ridge and pin. The information is used in some cameras'** Dual Program to optimize the shutter speed so as to minimize the effect of camera movement. Another diagnostic characteristic of an AI-S lens is its orange smallest aperture number on the ADR row - NOT just the normal aperture number row as some lenses happen to have (AI 16/2.8 e.g.). Be aware that new aperture rings (with orange smallest ADR aperture number) could have been retro fitted. Finally, the mounting ring has been "degraded" from chrome to aluminum. It is NOT possible to easily "AI-S modify" an AI or pre-AI lens since the major difference is internal - the nature of the stop down action! Only four cameras will distinguish between an AI and an MF AI-S lens; Nikon FA, F-301, F-501 & Nikon F4.

A 2.4kg MF AI-S 300mm f2.8 ED-IF has five screws. The MF 85mm f1.4 has six and the new ED-IF Micro Nikkor 200mm f4 also has SIX !

* Credit: -Hansen, Lars Holst-

An AI-S lens
compatibility Chart prepared by Lars.(New)

Nikon FA is the most sophisticated manual focus Nikon body prior to the arrival of the autofocus bodies and it is also the first Nikon that has full-fledged multimode features in P (Dual Programmed Auto -high speed and normal Program), S (Shutter Priority Auto - the first Nikon that has this feature integrated into the body), A (Aperture Priority Auto), M (Manual). And metering system is comprised of AMP (Automatic Multi-pattern), traditional Nikon's Centerweighted, Stopped-down and TTL flash metering.

The AI-S lens is an updated version of AI Nikkor lenses: in 1977, Nikon introduced AI-Nikkor lenses which feature full aperture metering via Nikon's "Automatic Maximum Aperture Indexing" or "AI" system. Just by mounting an AI lens on the camera, the maximum aperture is automatically indexed into the camera's metering system. All AI-type lenses feature a meter coupling ridge and a meter coupling shoe with two holes. Then in 1981, Nikon modified their entire line of AI-Nikkor lenses, so that they would be fully compatible with the upcoming Nikon FA's high speed program mode. These new lenses, called AI-S Nikkor, are easily distinguishable by (a) an orange minimum aperture on both regular aperture and aperture-direct-readout (ADR) scales and a special notch on the bayonet mount . In addition, the AI-S symbol appears on the front cover on the instruction manual for each lens.

When used with the Nikon FA in the programmed mode, AI-S lenses provide either a normal or high-speed program, depending on the focal length in use; in the shutter-priority mode, they give you uniform exposure control in broad scale of lighting situations (Although an AI or even an AI-modified Nikkor lens works in the shutter priority AE in the FA, but since the AI-S lenses are 'dedicated' Nikkor to work with such automation, it may be faster or more accurate in its exposure setting of aperture value on the lens by means of tripping the auto aperture lever on the body).

Nikon Series E lenses also have the same features as AI-S Nikkors, but do not have a meter coupling shoe.

AIS-Lens Mount relationship.jpg (21k)
Of course, older AI-Nikkor and AI-modified Nikkor lenses can be used with all current and older Nikon cameras, including the FA. Nikon's new series of teleconverters - the TC-201, TC-301, TC-14A and TC-14B - have been specially designed for AI-S Nikkor lenses, but can be used with older AI-type lenses, too. As soon as they are attached, they automatically switch the FA to the high-speed program in the programmed mode.

A) AI-S Meter Coupling Shoe (1) (Also usually referred as 'Rabbit Ears' - All AI & AI-S and in most cases, AI-modified Nikkor lenses have a tiny hole on each of the ears) but it may not be the case, because theoretically you can change the holed rabbit ear to fool others: before determining the lens type, use as many other references as possible to cross check it. B) Metered coupling ridge(2). AI (AI-S, series E, AI modified and AF) lenses have this ridge to couple with the meter coupling lever (3) on the camera body. Some cameras like FE2, EM, FG, FG20 and FA have a fixed and non-adjustable lever, thus, non-AI lenses need to be modified before they can be used on these bodies.; C) Lens mounting Index (4).; D) Focal length indexing ridge (5) couples with the focal length indexing pin (6) on the camera body. E) Lens type signal notch (7) provides info to the camera body by way of the lens type signal pin to differentiate between AI , AI-S lenses or Non-AI and AI-modified lenses (8); Lens locking detent (9) fits with the spinged lens release pin (10) for secure mounting of lens in use, pressing the lens release button will disengage and free the locking for lens release; F) Aperture stop-down lever (11) control the iris diaphragm(blades) when the Aperture coupling lever (12) trips for an selected aperture values during an exposure or in depth of field preview operation. G) Lens mount bayonet flange (13) securely locking the lens with the bayonet mount(14) of the body; H) Lens speed indexing post (15) relays info mechanically to the maximum aperture indexing lever (16) on the body (The lens is instantly stopped down to the computerized aperture position by a real-time aperture control signal. Also, until just before the exact moment of exposure, the actual lens aperture value is fed back into the microcomputer for precise shutter speed alteration, in case this becomes necessary).

There are some incorrect interpretations as regards the purpose of the levers and pins used in the FA in some websites and FAQs. Anyway, let me explain their respective purposes when used in the FA:

Signal Pins and Levers on the Nikon FA's Lens Mounting Flange

Update: Warren H. Hodson sent in his views on how AI and Non-AI Nikkors lenses would affect the AMP metering and Lars thought otherwise - some contradictory views over this subject.

Lens type signal pin (8) (The mysterious extra pin just above the lens release pin (10)):

The FA's lens type signal pin is used to distinguish Al-S Nikkor (and Nikon Series E) lenses from AI-Nikkor lenses. Between those two types of lenses, there is a slight difference in the travel of the aperture coupling lever, thus affecting the speed at which the diaphragm blades stop down and open up. Specifically, an AI-Nikkor lens tends to be stopped down to a smaller aperture than an AI-S Nikkor lens would be, especially when the scene brightness requires smaller apertures for P and S mode operations. That's why it's vitally important that the type of lens be distinguished via the lens type signal pin.

With an Al-S Nikkor (or Nikon Series E) lens, the lens type signal pin is not pushed in, because the lens has a special notch on the lens bayonet mount; the notch is so designed that it accepts the pin without pushing it in. An AI-Nikkor lens, on the other hand, doesn't have this notch and so the pin is pushed in. When the pin is pushed in, the aperture coupling lever on the camera body is electronically controlled to provide almost the same optimum exposure control as that of an AI-S Nikkor lens (Note: ALL AF Nikkor are AI-S).

Maximum aperture indexing lever (Lens Speed Indexing Lever) (16):

This lever transmits the lens maximum aperture signal to the camera body. The lens maximum aperture is the main factor in deciding the amount of vignetting or light fall-off in the off-center areas. Because the FA measures the brightness in those off-center areas, the light metering level in the off-center areas must be compensated to provide correct light value data for the FA's automatic multi-pattern metering. And so this information on maximum aperture becomes indispensable for the FA's automatic metering system. Also, this signal is essential in determining the program line that is subject to change according to the lens maximum aperture. It is also used to display the correct f-number in the LCD in the S mode. Lenses without this signal (i.e. AI-modified Nikkor) will not display the selected f-number, instead, only "F..." will appear in the LCD.

This is
not the first time a maximum aperture indexing lever has been used on a Nikon camera - the Nikon EM and FG feature such a lever. The EM's lever is used to inform the Speedlight SB-E of the aperture in use, whereas the FG's lever provides a warning indication in the P mode when the lens is not set at f/11 or a smaller aperture. This incorrect aperture warning is also available with the FA in the P and S modes, i.e., "FEE" display via LCD.

Focal length indexing lever (5 & 6):

Al-S Nikkor and Nikon Series E lenses of 135mm or longer, and Nikon Teleconverters TC-201, TC-301, TC-14A and TC-14B have the focal length indexing ridge (5) corresponding to the FA's focal length indexing lever. When one of these lenses or teleconverters is attached to the FA, the protrusion pushes the lever, thus transmitting a signal that the normal program should be shifted to high-speed program in the P mode. The lever also signals that vignetting due to the lens' long focal length should be compensated for.

More? See the NEW the Nikon F4 sites

Check here for graphical illustrations on AI, non-AI, AI modified and AI-S lenses.

The following lenses are usable with the Nikon FA:
(Also check the
lens compatibility chart for Nikon FA and Nikon F4)

AI-S Nikkor lenses
Nikon Series E lenses
AI-Nikkor (including AI-modified Nikkor) lenses
Reflex-Nikkor 500mm f/8
PC-Nikkor 28mm f/3.5
Medical-Nikkor 120mm f/4 IF
Reflex-Nikkor 1000mm f/11 (No. 143001 or higher)
Reflex-Nikkor 2000mm f/11 (No. 200311 or higher)
PC-Nikkor 28mm f/4 (No. 180901 or higher)
PC-Nikkor 35mm f/2.8 (No. 851000 or lower or No. 906201
or higher)
Zoom-Nikkor 180-600mm f/8 ED (No. 174167 or higher)
Zoom-Nikkor 200-600mm f/9.5 (No. 300491 or higher)
Zoom-Nikkor 360-1200mm f/11 ED (No. 174088 or higher)

Note (1): The last seven lenses having serial numbers not listed above cannot be mounted on the FA or subsequent Nikon models, especially the earlier entry AF models like F401, as they may hit the camera's meter coupling lever. However, they can be used after modification. In addition, AI-modification of most non-AI lenses having a meter coupling shoe is available. Do not attempt to mount older Nikkor lenses which have not been AI-modified, as they might damage the camera.

Note (2): The following lenses cannot be used on the FA even If they are modified to have the Al facility: 55mm f/1.2 (No. 184711-970110) 28mm f/3.5 (No. 625611-999999); 35mm f/1.4 (No. 385001-400000). Note: Thanks, Lars..

Some changes have been implemented for each model shown in the list for reference on the F mount:

Model Bayonet mount Lens mounting index
EM Changed from June 1981 Not changed
FM2 Changed from March 1983 Not changed
FG Changed from the initial stage Changed from the initial stage
FE2 Changed from the initial stage Changed from the initial stage
F3 & F3T (Champagne Finish) Changed from January 1983 Changed from August 1983

Note: the pre-modified bayonet mount should not be installed to the camera of programmed exposure control.

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Several events carried significant influence in the development of Nikon SLRs: Pre-AI (Nikon F, F Photomic, T, Tn, FTn; Nikkormat FT, FS, Nikkormat FTn; Nikon F2, F2 Photomic, F2 Photomic S, F2 Photomic SB; Nikkormat EL, FT2, ELw); AI (Nikon F2 Photomic A, F2 photomic AS; Nikkormat FT3, Nikon EL2, Nikon FM, FM2, FM2n, FE, FE2, EM, FG, FG20); AI-S (Nikon FA, F301); AF (Nikon F501, 801, F401s, F601, F601m, 801s, F401s, F90, F4 Series); AF-D (F90x onwards...)

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Index Page
  Special Application lenses:
Micro-Nikkor Lenses - 50mm~55mm -60mm 85mm -105mm 200mm Micro-Zoom 70-180mm
Perspective Control (PC) - 28mm 35mm PC-Micro 85mm
Dedicated Lenses for Nikon F3AF: AF 80mm f/2.8 | AF 200mm f/3.5 EDIF
Depth of Field Control (DC): 105mm 135mm
Medical Nikkor: 120mm 200mm
Reflex-Nikkor Lenses - 500mm 1000mm 2000mm
Others: Noct Nikkor | OP-Nikkor | UV Nikkor 55mm 105mm | Focusing Units | Bellows-Nikkor 105mm 135mm
Nikon Series E Lenses: 28mm35mm50mm100mm135mm | E-Series Zoom lenses: 36~72mm75~150mm70~210mm

MF Zoom-Nikkor Lenses: 25~50mm | 28~45mm | 28~50mm | 28~85mm | 35~70mm | 36~72mm E | 35~85mm | 35~105mm | 35~135mm | 35~200mm | 43~86mm | 50~135mm | 50~300mm | 70~210mm E | 75~150mm E | 80~200mm | 85~250mm | 100~300mm | 180~600mm | 200~400mm | 200~600mm | 360~1200mm | 1200~1700mm

Tele-Converters: TC-1 | TC-2 | TC-200 | TC-201 | TC-300 | TC-301 | TC-14 | TC-14A | TC-14B | TC-14C | TC-14E | TC-16 | TC-16A | TC-20E

Recommended links to understand more technical details related to the Nikkor F-mount and production Serial Number: by: my friend, Rick Oleson by: Hansen, Lars Holst

Recommended Reading Reference on Nikon cameras and Nikkor lenses
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Credit: To all the good people who has contributed their own experience, resources or those who are kind enough granting us permission to use their images appeared in this site Note:certain content and images appeared in this site were either scanned from official marketing leaflets, brochures, sales manuals or publications published by Nikon over the years and/or contribution from surfers who claimed originality of their work for educational purposes. The creator of the site will not be responsible for may discrepancies arise from such dispute except rectifying them after verification."Nikon", "Nikkormat", "Nippon Kokagu KK" & "Nikkor" are registered tradename of Nikon Corporation Inc., Japan. Site made with an Apple IMac.