N/AI-S

<p>What does this mean when found on the back of a lens<br>

I thought it meant Non-AI...but I have a lens with this marking that fits well on my F100</p>

<p>Nikon AI-S</p>

<p>Non-AI was never an official designation.</p>

<p>D'oh. There are so many other random letters on Nikkor lenses that it didn't occur to me that one of them would stand for something obvious - and this was bugging me. :-) Good call, James.</p>

<p>I would venture to guess that this isn't a Nikkor, but a third-party lens. Nikon wouldn't have bothered saying "N/AI-S".</p>

<p>I was going in 2 directions when I first saw this description on the back of my lens<br>

1. Non - AI/S<br>

or<br>

2. Nikon (mount) AIS<br>

as my third party lens has 2 sets of aperture values...and the N/AI-S, and does fit my F100 well, then I think we are indeed looking at N/AI-S meaning Nikon AIS<br>

least i'm hoping!</p>

<p>Can you tell us anything else about the lens? I wouldn't have expected a third-party lens to have the AI-S nomenclature. Given focal length and aperture (is there a serial number?) we might be able to find a picture to compare against. Of course, posting a picture of yours would be interesting too. I need to go home before I can check my 135 f/2.8 AI-S for what's written on it...</p>

<p>I don't think anyone ever described anything as "Non-AI-S". Usually it's "NAI" for non-AI, "AI", or "AI-S". On a third-party lens, N/AI-S has to mean "Nikon AI-S".</p>

<p>I don't see why it should be surprising for a third-party lens to be identified as AI-S. All of Nikon's AI lenses were revised to be AI-S in the early '80s; a third-party maker who didn't follow suit would risk being seen as behind the times. Here is an example of a third-party lens with exactly that designation (scroll down for shots of the lens itself):</p>

<p>http://regex.info/blog/2010-07-13/1564</p>

 

<p>Craig: I stand corrected, especially with the 125mm APO-Lanthar as such a legendary example; I wish I could claim not to believe you, and ask you to send me a copy to verify. :-)<br />

<br />

My reasoning was just that I expected Nikon's "AI" and "AI-S" terminology to be internal, just as "AF-S/SWM" and "VR" are "HSM" and "OS" in Sigma terms - I thought other manufacturers might have chosen a different way to state compatibility. Ah for the good old days when terminology actually made sense...</p>

<p>If it's a third party lens, like that nice old Vivitar Series I, and it says N/ai-s on it, it means it's a Nikon AIS lens. If you have it in your hand, you can confirm this by looking first at the back side of the aperture ring, where you should see that it is partly milled out, so that a boss appears in just the right place to push your camera's AI tab sideways. The rabbit ears will have holes in them, and there will probably be a second little set of numbers on the aperture ring, to provide the viewfinder readout on cameras (not including the F100) that have an ADR window. And finally, if it's an S, there will be a little semicircular depression milled into the back side of the mount, just to the right of the locking-tab slot as you face the back side of the lens. That little milled depression is present only in AIS lenses (not in plain AI) and is utterly unneeded by your camera, but it appears only on an AIS lens.</p>

<p>"NAI" meaning "not AI" is a description used sometimes by eBay and other used gear sellers. But stamped on a 3rd party lens, "N/AI" means "Nikon AI" and "N/AI-S" means "Nikon AI-S".</p>

<p>Nikon itself doesn't use those designations, because it doesn't have to label its lenses as being for Nikon cameras. Also, pre-AI lenses were made before AI was a thing, so they would not have been sold as "not AI" because that wouldn't have been a meaningful description at the time. After Nikon started selling AI lenses they changed over the lineup pretty quickly (which wasn't hard because all it meant was a modification to the shape of the aperture ring and a new prong design) and even offered a conversion service that swapped the aperture ring out for a new one.</p>

<p>thanks all - great description andy - a 'n/ai-s' I will go - fearlessly into the land of 3rd party lenses - wish me luck!</p>

<p>I completely agree with Andy.<br>

Nobody ever described original Nikon F-fitting lenses as Non-Ai for the simple reason that Ai coupling didn't exist at that time! In any case the correct description should be pre-Ai.<br>

NAI (or N/Ai) has <em>always</em> stood and still stands as an abbreviation for Nikon Ai coupling. Likewise NAIS, N/Ai-S or variations thereof refer to Nikon Ai-S lenses. The moronic descriptions on *Bay can be safely ignored.</p>

<p>Actually Nippon Kogaku devoted much advertising to Ai and Ai-S lenses they were introduced, along with much media (magazine) coverage. The Ai mount eliminated the back-and forth "Nikon twist" to index the exposure meter with the lens' maximum aperture. It also enabled aperture information in the viewfinder (except for FT-3, EL2 and later the EM, FG, and FG20.) And what else would they call the conversion rings designed for pre-Ai lenses if they did not use the Ai monikor?</p>

<p>Ai-S of course meant a linear aperture mechanism to facilitate Program and Tv modes. The instruction sheets that came with the lenses were all specifically marked Ai or Ai-S.</p>

<p>https://nikoneurope-en.custhelp.com/app/answers/detail/a_id/1160/~/what-is-the-difference-between-nikon-manual-lenses-types-%28ai,-ai-s-etc%29</p>

<blockquote>

<p> It also enabled aperture information in the viewfinder (except for FT-3, EL2 and later the EM, FG, and FG20.)</p>

</blockquote>

<p>The Pre-AI aperture coupling is more complex than the AI coupling and thus it was the pre AI coupling that can provide aperture information in the body. The aperture scale in the pre-AI cameras like Nikon F and some version of the F2 is built in to the camera body. The AI camera doesn't have the aperture scale built in but use the ADR to read the aperture number directly on the lens.</p>

<p>Alas, the above is not the case for a Nikon Photomic FTn, or any other Photomic F I can recall, which provides no aperture information in the viewfinder. This is one of its unfortunate drawbacks, made worse by the overhang of the meter head which hides the numbers on the lens. Because most of the lenses have well detented full-stop aperture rings, it becomes fairly easy to determine aperture by counting clicks.</p>

<p>Because the absolute aperture and the indexing are separate in the pre_AI system, a camera that is equipped for it can read absolute aperture from the position of the meter follower claw, which is always at F 5.6. The Pre-AI meters for the F2 do this.</p>

<p>Since the pre-AI meter claw is always set at f 5.6, information to the camera on what a lens's maximum aperture is must be entered separately. In the original Photomics it was selected by hand, essentially offsetting the meter's ASA rating. On the Photomic FTn, it was selected by twisting the aperture ring, a considerable advance. On an FTn, if you neglect to index the lens, meter readings will be wrong even though every lens that couples to the meter has its tab at F 5.6, because the meter is not reading absolute F stop information. Since you view and meter at wide open aperture, the meter is reading offset from that maximum aperture, which it must be informed of first. The meter actually never needs to know absolute aperture, and displaying it is only a convenience for users.</p>

<p>In the AI system, the meter follower is spring loaded, and the location of the tab it on the back of the aperture ring which it hits varies with the lens's maximum aperture, so separate indexing is not needed. But there is also no coupling between lens and camera that registers absolute aperture.</p>

<p>By the way, silly me, I have gotten so many bits and pieces of hardware over the last year that I temporarily forgot (forgot? Yes, mea culpa I forgot!) that I actually have a Vivitar Series I lens for the Nikon! It is a 28-90 that I bought for nearly nothing because it has a nasty mark on the front element. For the record, this lens bears the marking "N/AI-S" and it is absolutely, without any doubt, a compatible AIS lens which works just fine on my F3, F4, and FM10. It's unforgivable that I should have so many lenses that I can't keep them all straight. I must need another Nikon camera. </p>

<p> </p>

<p>By the way, a little correction to the above: It seems the Nikon F Photomic T and TN finders, at least, do have an aperture readout, although it is not in the display window. There is an aperture window on the back side of the finder. Since earlier finders require you to set both finder and lens to F5.6 before installing it, it's required. You need not preset either lens or finder on an FTn, so I guess they left it off.</p>