AI conversion kits - are they really just the aperture ring?

[whatdoido]

Are AI conversions for K lenses are as simply as an aperture ring replcement?  And if so, would the K-AI conversion kit (aperture ring) be the same as the AI ring?

Example:  would the 20mm f/4 K conversion kit have the same aperture ring as the to 20mm f/4 AI?  This kit was listed in the cheaper tier of conversion options based on Roland's info http://www.photosynthesis.co.nz/nikon/aimod.html which suggests labour and parts (and shippping) were reasonable simple.


The background to this is I have a Nikkor 20mm f/4 AI but it's got some problems but have an option on a 20mm f/4 K that is in good condition - I wonder if i can simply swap the aperture rings (from AI onto the K) and have an AI'd K lens.  Milling/filling the K ring is something I dont want to do since I have an AI aperture ring.

[David H. Hartman]

Take care to soften the white locking "paint" on the screws. Do NOT strip the heads or torque them off! I did a DIY conversion of a NIKKOR-P·C Auto 1:2.5 f=105mm. I torqued off the head then with the aid of a vacuum cleaner and a pin vice I somehow drilled a tiny hole in the torqued off screw. I could not buy an extractor small enough so I used a larger drill to bind in the hole and successfully extracted the broken screw.

Stupid! Damned lucky! Learn from my mistake!

Later I used acetone to soften the Loctite thread locker (white, permanent?). A camera repairman friend use a small. butane soldering iron to heat the screws.

Dave

It's been so long but to my knowledge an official Nikon AI conversion kit contained only an aperture ring, AI style rabbit ears and a few screws. John White may still be doing AI conversions as of March 2026.

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I can't answer the original question. Someone with more experience will surely answer. If you are already experienced with the procedure for removing the rear bayonet screws please accept my apology.

My advice is pickup a clean, used NIKKOR 20mm 1:3.5 AIS as they are highly resistant to flare and ghost and can be turned directly into the sun.

[David H. Hartman]

here is my go to short lens review site...

http://www.naturfotograf.com/lens_wide.html

[pluton]

Are AI conversions for K lenses are as simply as an aperture ring replcement?  And if so, would the K-AI conversion kit (aperture ring) be the same as the AI ring?

Example:  20mm f/4 K conversion kit have the same aperture ring as the to 20mm f/4 AI.  This was listed as the cheapest conversion option based on Roland's info http://www.photosynthesis.co.nz/nikon/aimod.html which suggests labour and parts (and shippping) were reasonable simple.


The background to this is I have a Nikkor 20mm f/4 AI but it's got some problems but have an option on a 20mm f/4 K that is in good condition - I wonder if i can simply swap the aperture rings (from AI onto the K) and have an AI'd K lens.  Milling/filling the K ring is something I'd like to avoid since I have an AI aperture ring.

My limited experience swapping K and Ai aperture rings is that the Ai kit ring can (obviously) swap onto a K lens, and the K ring should go onto the Ai lens without issue.  My experience: I have switched K to Ai, and Ai to K, on a 28/2.8 K/Ai lens a few times between the two copies of the lens. 

[whatdoido]

Dave - thats a name I havent seen since the strobist forum days!  Yes i'm ok with dissaembly/tear down of these lenses, I have a number of the 20mm f/3.5 AI already (still have one) but all of them aren't that sharp until you get f/8 and beyond and even then its just "ok" whereas direct comparison with the f/4 is sharper, even at f/4 and f/5.6 for both near and far.

https://whatdoineed2do.blogspot.com/2026/01/widely-regarded-nikkor-20mm-f4-ai.html

Pluton - thanks.  Roland's site also notes the 28mm ff/3.5 kit was 18$ but thats not a defnitie indicator.  if the K seller can do a good price i may just chance it.  The only reference I have is a factory AI ring on a 55mm f/3.5 Auto (I dont have the original aperture ring though) where the installed aperture ring just looks like the one of the 55mm f/3.5 AI although I know there's K variant and so not direclty comparable.