An economical wide alternative: 28mm f/3.5 AI

The 28mm f/3.5 has a long history reaching back to 1960, with the Auto-H, and cumulating in the Nikkor 28mm f/3.5 AI/AIS of the late 70s/early 80s. All variations had a 6/6 design although the Auto-H and the AI/AI-S having different optical formula. By the time the AI/AI-S was released in 1977/1981, it was already seen as the economical 28mm with its slower f/3.5 max aperture with the f/2 K and f/2.8 K/AI making its debuts in 1975 and 1974 respectively.

The f/3.5 AI-S was sunset in 1983 by which time the very well regarded 28mm f/2.8 AI-S had been released. Over time, the 28mm f/2.8 AI-S reputation (and its long production run) keeps it in conversations but if you were to consider a manual 28mm, is the slower f/3.5 worth considering?



The 28mm f/3.5 AI and AI-S lenses share the same optical formula but different barrel construction so picking up either is a good bet. They are nearly identical in size/weight but the AI has a 200 degrees focus throw compared to the 90 degrees of the AI-S.


^{Nikkor 28mm f/3.5 AI optical cross section}

Incredibly, the 28mm f/3.5 AI lens is very sharp wide open with very good contrast. This is indeed a surprise given the f/2.8 AI-S is renowned for sharpness.




^{centre crops, shot at 1.5ft - click for full size}

Servicing

As with any aging 40+ year AI lens, repairing / servicing 28mm f/3.5 AI is almost inevitable and this lens is quite easy to work on. This lens constructions follows most wide-normal AI lens so if you've worked on the 35mm f/2 AI or the 50mm f/2 AI this will be quite familiar.

• To start, remove the rubber focus grip to expose a lacquer seal securing the focus ring. Apply acetone/IPA to the hole and wait before twisting off.
  
  
  
  
• Once removed, extend to MFD to access the set screw on the front lens retaining collar (including the nameplate) - once the retaining collar is removed you can remove the lens objective as a single unit and set it safely aside.
  
  
  
  
• Remove the rear mount and the aperture ring as usual - there are no gotchas here - to expose the aperture coupling pin; unscrew this and pick out the aperture fork.
  
  
  
  
  
  
  
  
• Remove the 3x screws and remove the focus ring. These 3x screws are where you'd adjust infinity focus.
  
  
  
  
• From the rear, remove the chrome grab ring - you don't need to remove the ident spring if you're lazy, simply press it down before sliding the grab ring over. Next remove screws securing the focus distince scale. The helicoid screws are accessible without remove the distance scale but its easier to remove this.
  
  
  
  
• Mark an infinity alighment mark on the central and rear helicoids.
  
  
• The helicoid key has a lip that faces the rear of the lens. Remove the helicoid key screws and carefully extend the focus towards MFD so you can push the helicoid key out - store safely
  
  
  
  With the helicoid removed, you can collapse the central helicoid to get a reference for reassembly but because of the 50 year old grease, this may not be 100% upon reassembly.
  
  
• Separate the rear and central helicoids, marking separation on the central helicoid as aligned the the rear helicoid (infinity) reference mark
  
  
  
  
• Separate the inner and central helicoid THROUGH the central helicoid (as the inner helicoid going to to the front of the lens). YOu can't separate through the rear. Mark the inner helicoid aligned to the (infinity) reference on the central helicoid
  
  
  
  
• Clean the helicoids with lighter fluid, kitchen degreaser, kitchen dish soap and then final clean with IPA
  
  
  
  
  
  
• Apply a very thin layer of NLGI #00 grease to the inner helicoid and remate - ensure this is smooth and light before remating the outer helicoid. On the central helicoid apply a thin layer of the same grease but adjust to taste as this will the most impact on the focus feel when fully assembled.
  
  Remember to lightly grease the helicoid key and its slot.
  
• Once assembled to attaching the focus ring, do not secure the screws but go and calibrate your inifinity focus
  

Optics

The optics are set in 6 elements in 6 groups, with the aperture blades sitting behind the 3rd element. The elements are in set logically into 1st/2nd elements as one removal block and the 3rd element. The final 3 elements are extracted from the rear and aside from the usual lacquer on a first logical block, access relatively easy.



Be careful when removing the rear element - its almost impossible to tell which way it should face, although if you install it wrong test images will show you.


^{3rd element}

As with all rear elements, be careful of use an air blower on the 2nd-last element - blowing on it will invariable kick up the spacer and element and can confuse you for orientation. Luckily the 5th element here is clear and the spacer has a flatter edge that sits on the 5th element.


^{5th element sitting behind a spacer}

Conclusion

I was surprised by this lens - there's some writeup on the internet about this lens but I don't trust most of those reviews outside of Bjorn Rorslett who did give this a 5/5 but given his positive writeup of the f/2.8 AI-S I didn't expect the f/3.5 to be that good. Certainly if cost was a factor - and the f/3.5 AI can be found around 1/3/ to 1/2 price of the f/2.8 AI-S - there would be no hestitation in recommending this f/3.5 AI.