Ai conversion of non-Ai Nikon lens

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Ricoh

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‪I've recently acquired a Nikkor S.C Auto 50mm f1.4, plus a rather nice, clean, FM2. The lens has clearly had a DIY AI conversion, as can see by the file marks on the aperture ring.

When mounting the lens to the camera I'm concerned that there's minimal engagement of the modified (filed down) aperture ring with the meter coupling lever; a fraction of a mm as far as I can determine.

Ideally an OEM AI conversion kit would be the solution, but that's like finding hen's teeth (is that an apostrophe before or after the letter s 🤔).

In lieu of the ideal OEM kit, I'm thinking of sticking something to the modified aperture ring such that there's improved engagement with the tab, ie like the 'kosha' Nikon AI or AIS aperture ring. Any ideas?
 
You would be better off just finding a 50 1.4 Ai or Ai-S. The problem with the home made Ai is you don't have any idea if metal shavings fell into the lens in the process. The non-Ai 50 1.4 was very popular and widely available but not one of Nikons better lenses
 
madNbad said:
You would be better off just finding a 50 1.4 Ai or Ai-S. The problem with the home made Ai is you don't have any idea if metal shavings fell into the lens in the process. The non-Ai 50 1.4 was very popular and widely available but not one of Nikons better lenses
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I hadn't thought of that tbh, thanks. Might do what you suggest and sell the one I have.
 
That being said, let me ask here - in 2020, who would be the best person to contact with regard to AI conversion? Especially with rare and/or oddball lenses.

For example, I have an 8mm f/2.8 circular fisheye I would like to get converted. That one is probably not a problem for a professional. However I also have several older F-mount lenses that have an elongated rear "shroud" (first production batch). These lenses do not mount to any camera except the F and F2. I would also like to get these converted but will probably be a much less routine procedure.
 
AAlfano said:
I'm curious about this as well. Given the rarity of OEM AI conversion parts, could the parts be salvaged from a damaged AI or AI-S lens?
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The problem is the mount on the non-Ai lenses is recessed further into the lens body creating a bit of overhang on the body mount. Dust intrusion was a concern for the engineers so the earliest Nikkor F mount lenses had the mount recessed enough when attached to the camera the flange covered the entire body mount. The overhang was reduced gradually and was gone with the introduction of the Ai lens. It's not a simple mater of just changing the mount but also either shimming or trimming for the lens to mount properly and engage the Ai mechanism.
 
AI conversions

AI conversions

In 1977, I had a 50mm 1.4 like yours from about 1961-2, as well as three other Nikkors recently purchased. I was able to send the new lenses to Nikon USA for AI conversion, but Nikon never made a conversion kit for the early 50mm 1.4. After many years of using my 50mm 1.4 to decorate my equally unused Nikomat FT2, I sent it to John White to do his conversion thing. Very clean job; $25. White has been doing these conversions since Nikon terminated its conversion program for lack of parts, around 1979.
 
John White did two AI conversions for me in 2015. Perfect job, both work flawlessly. Quick and inexpensive.

G
 
Ricoh said:
‪I've recently acquired a Nikkor S.C Auto 50mm f1.4, plus a rather nice, clean, FM2. The lens has clearly had a DIY AI conversion, as can see by the file marks on the aperture ring.

When mounting the lens to the camera I'm concerned that there's minimal engagement of the modified (filed down) aperture ring with the meter coupling lever; a fraction of a mm as far as I can determine.

Ideally an OEM AI conversion kit would be the solution, but that's like finding hen's teeth (is that an apostrophe before or after the letter s ��).

In lieu of the ideal OEM kit, I'm thinking of sticking something to the modified aperture ring such that there's improved engagement with the tab, ie like the 'kosha' Nikon AI or AIS aperture ring. Any ideas?
Click to expand...

I have converted several lenses now and find that the most difficult part of the job (and that is not difficult at all) is to get the ring off the lens, then back on properly afterwards - the secrets are (a) knowing which screws to undo - on some lenses which have screws on the bottom of the lens, one of these is a screw holding an internal spring in place and this should not be removed and there is nothing apart from its position to tell you it is not a base-plate mounting screw which should not be unscrewed. And (b) setting the lens to its closest focusing distance is useful although this is not necessary with all lenses but it is a good practice to work in a standardized manner so you get into the habit. BTW setting the lens to either minimum or maximum aperture is a useful though not necessary practice too as it means you automatically know how to align the aperture ring when you are putting it back on the camera.)

All of that is a bit of an aside however. The new recess for AI coupling has to be exactly the right place of course, but apart from this it must also be just deep enough to provide clearance for the camera's AI coupling lever to move freely without jamming. I have only had one lens in which it needed deepening a little more to facilitate this. This was in a lens I bought which someone else had done before I bought it. Poster "madNbad" describes an "overhang" on most non-AI lenses. I have observed this too. Because of this overhang there is usually plenty of rim overhanging on the old lens to engage with the coupling lever when the recess is filed. It is this overhang which gets filed or machined for the AI recess.

Having said this, I have two Nikkor native non Ai lenses both of which I have converted. One is a Nikkor S.C Auto 50mm f1.4 - like yours and the other is the later "K" version of the lens (the one with a rubber focus ring - the last non AI version of this lens I believe). With neither of these lens is the "overhang" very deep - only perhaps one mm. I believe (but have not checked) other Nikkors may have a little more than this. This means the recess for the camera's AI lever to engage with must of necessity be shallow and of necessity, the AI lever can only engage by a relatively small amount otherwise it might bottom out / catch on the lens' internal silver baseplate.

In short the camera's AI coupling lever can only engage by about 1 mm max.......... but I have never quite had one of the sort you describe - i.e. in which it engages by "a fraction of a mm" as you describe it . But then again these days, I always shoot with a Nikon D700. I have not tried other camera bodies to see how they function.

This leads me to the thought that your problem (if it is a problem - and I am not sure it is) may be with the camera not the lens. Here is a thought - if someone previously had tried to mount a non AI lens on your camera body and your camera body is not designed for this, there is a probability that this might have slightly bent the AI coupling lever out of proper alignment. (Such damage is the major reason one is usually advised not to mount a non AI lens on an AI-only body - though a few older bodies will allow either as the AI coupling lever hinges out of the way when a non AI lens is mounted) It's something to look into as this could mean a different solution is needed - i.e. adjusting your camera not your lens. Just a thought!

Here is another thought - just ignore it. You may be worrying over nothing. If the camera's AI coupling lever is engaging correctly with the lens then this is all you need even though it is only by a tiny amount.
 
Thanks Peter, I've found the explanation and your thoughts on the possibility of other issues, such as the tab being bent, very helpful; something for me to investigate further.

Very difficult to precisely determine the amount of engagement with an engineering ruler due to the confined space, but it looks marginal. I suspect it's sub 1mm.

The camera was supplied with both the 50mm described, plus an E series AI-S 36-72 f3.5, and by comparison the AI-S engages with the camera tab more positively. I'm trying to determine whether it's a difference in wall thickness of the aperture ring and/or possibly the overhang.

I've been in touch with the eBay Guy James24 linked above, describing the perceived problem, if indeed it is a problem. He replied quite quickly actually, mentioning issues with wall thickness, but I'm not certain if he was talking about the S.C Auto. I'll correspond with him again tomorrow as it's just gone midnight here. He mentioned that if wall thickness is part to play there is another mod that can be performed.

I'll have to weigh-up cost and whether it's more appropriate to get an AI or AI-S version as a replacement.

PS hope you haven't been affected badly by the fires. It's on the news here almost every day.
 
Regarding the important question of hen's teeth vs hens' teeth, the apostrophe would be before the 's' if the phrase were "...a hen's teeth..." With the 'a' denoting a singular hen. If there is more than one hen, then it would be "...hens' teeth..." Thanks also for not posting "lense's" or "camera's" or "chicken's" as a plural.
Phil Forrest
 
Ricoh said:
Thanks Peter, I've found the explanation and your thoughts on the possibility of other issues, such as the tab being bent, very helpful; something for me to investigate further.

Very difficult to precisely determine the amount of engagement with an engineering ruler due to the confined space, but it looks marginal. I suspect it's sub 1mm.

The camera was supplied with both the 50mm described, plus an E series AI-S 36-72 f3.5, and by comparison the AI-S engages with the camera tab more positively. I'm trying to determine whether it's a difference in wall thickness of the aperture ring and/or possibly the overhang.

I've been in touch with the eBay Guy James24 linked above, describing the perceived problem, if indeed it is a problem. He replied quite quickly actually, mentioning issues with wall thickness, but I'm not certain if he was talking about the S.C Auto. I'll correspond with him again tomorrow as it's just gone midnight here. He mentioned that if wall thickness is part to play there is another mod that can be performed.

I'll have to weigh-up cost and whether it's more appropriate to get an AI or AI-S version as a replacement.

PS hope you haven't been affected badly by the fires. It's on the news here almost every day.
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Thanks Ricoh. I am glad it may have helped.

As to the fires, here you got me onto a sore point of mine. :^( . They are terrible and still ongoing including in my state, South Australia, though I imagine most international media attention is focused on the eastern states where they have been out of control for many weeks.

Sadly many of the fires are deliberately lit and it's compounded by lax governments failing to institute proper risk mitigation measures such as fuel load reduction burns during wetter seasons when these smaller less intense fires can be controlled. Australian flora has adapted to fires over the millenia and cope well with smaller, less intense fires which paradoxically trigger new growth in many species. More intense fires on the other hand, kill them.

Not so sure about fauna though and I hate to see animals suffer but even here, the less intense fires (which can still come after fuel load reduction - natural or otherwise ) allow them to escape much more readily though there are inevitably some casualties and victims.

During Australia's history bushfires came commonly - due to lightning strikes etc and these acted to clear off forest floor fuel and were a natural way of reducing risk of major conflagrations. Due to modern firefighting, which puts those fires out and governmental practices, which seem purpose designed to allow fuel to build up (advocates love the idea of what they think is a natural bushland but which in reality is not natural at all as described above) the risk of disaster arising from those fires which do occur (and they always do) is now far greater. BTW it is not just me saying this - several previous post disaster judicial inquiries have established the above. Predictably though nothing much has been done as governments respond to public opinion which is shaped by media headlines and the zeitgeist of the times more than to rational analysis. I spent my working life in public policy areas and learned that good public policy should be based on facts and evidence not emotion and shallow impressions. (Anyway, here endeth my diatribe). :^)

What I actually meant to say is that I am located in Adelaide - our state capital and the worst I have had to contend with is occasional heavy smoke and smog when a cool change blows smoke north from Kangaroo Island, a large island off our south coast which is also badly affected by fires with about 50% of the island now ash and debris.
 
madNbad said:
The problem is the mount on the non-Ai lenses is recessed further into the lens body creating a bit of overhang on the body mount. Dust intrusion was a concern for the engineers so the earliest Nikkor F mount lenses had the mount recessed enough when attached to the camera the flange covered the entire body mount. The overhang was reduced gradually and was gone with the introduction of the Ai lens. It's not a simple mater of just changing the mount but also either shimming or trimming for the lens to mount properly and engage the Ai mechanism.
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Thanks for the reply!
 
I would like to thank all for replying. Most helpful. I'm currently in email discussion with Marcel on eBay that James24 referenced.
 
With no close-up photo of the OP's lens to see how the filing job has been done, this is a 19 clueless posts thread to just speak in the vacuum for the sake of it.

The FM2 coupling ring is spring loaded with a strong detent. So, as tiny the contact area between the camera coupling dot and the lens aperture ring is, it will work and the camera coupling tab will stay linked to the file-made lens coupling flange. The problem here would be with an unsufficient filing job which could be prone to have the camera plastic coupling tab snap and break when mounting the lens or turning the lens aperture ring.

On original Ai lenses the coupling flange is of about 0.9mm deep and the actual contact area with the FM2 coupling tab is of about 0.6mm deep when the lens is mounted (just checked this on my own gear which is at hand).

Using the lens as it is will work, won't damage anything, and won't cause metering problems.
 
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