A junk-bin Nikkor 135mm f/2.8 AI revived

The Nikkor 135mm f/2.8 AI was released ~1979, and whilst it seemed to have been shadowed somewhat by its 105mm f/2.5 AI-S sibling, still had a lengthy production run stretching into the early 2000s. Whilst I didn't have a need for this focal length, when I saw a junk condition lens for £15, it was hard to turn down even if was just to tear it down to see how these lenses worked.

How bad was the lens

The lens was sold in a very poor, dirty condition: the barrel had significant wear, the iris was responsive and the focus ring was well dampend and smooth but the front element had a small number of chips in it along with a severely compromised lens coating - the worst aspect was that it was obvious that someone had previously been in the lens as the front element was not secured in place, with it rattling in the optical housing. After I got my hands on it, and stripped it down to clean the lens elements with hydrogen peroxide, soap and then IPA, I could see no signs of fungus.

Since it was mostly the front lens group I wanted to attack, removing the front hood and front element retaining rings I could let gravity remove the front element. It was possible to unscrew most of the objective from the lens which separates the middle lens groups from the iris mechanism from this point: the middle group is can be seperated with a lens spanner for the large copuplet/glued element and hand unscrew the 3rd element for cleaning.


^{remains of the lens coating with red tint around the edge of front element}

With these front 2 lens groups out the way, with the aperture mechanism/irus still secured in the lens, I was able to use a hydrogen peroxide soaked cleaning supply to clean down the inside of the barrel followed by an IPA wipe down before reassembly.

However, the entire lens objective is secured to the lens barrel by 3x JIS 000 screws that you access when you remove the bayonet mouunt - once unsecured, the front hood retaining ring can be spun off and the optical block can be eased out of the lens barrel.

Alternativly if you only require access to the rear element this is easily accesible once you remove the bayont mount and can loosen it with a lens spanner and manually unscrewing it from the iris mechanism.


^{Rear bayonet mount removed, rear element still in place and view of objective securing screws}

Access to the securing screws is made easier if you unscrew the rear element, with them visible below at 4,8 and 11o'clock positions.



Reassembling the lens objective correctly the front element was reseated correctly and secured with its retaining ring meant it no longer rattled. It's not obvious why the previous owner took out the front element but I'd guess they were trying deal with the damaged lens coating without success and then got lost with reassembly.

How does a sratched and compromised lens coating affect the image

A number of years ago, LensRentals published a post showing relatively minimal image quality impact for a cracked front element and whilst not the same we expect the front element's compromised coating would impact the contrast and ghosting of images. Thankfully all the other lens elements in the 5/4 construction were clean and fine, except for a minor cleaning mark on the rear element. How much loss of contrast was the next question.


^{same camera shot as raw, colour corrected and exported with default options as jpeg, top: kit lens 55mm @ f/5.6, bottom: 135mm f/2.8 AI @ f/5.6}

As expected, the compromised lens coating has had an impact to the image quality resulting in loss of contrast with a 1980s soft focus/soft glow look to image. At wider apertures, contrast is even worse:


^{135mm f/2.8 AI @ f/2.8 and f/4.0}

Correcting the image with levels adjustment helps a little but the soft focus/soft glow is still evident.


^{kit lens image left, 135mm image right with levels adjusted in CNX2}

Sharpness is quite good even wide open but again the damaged front element results in a lack of contrast that detraccts from what a better preserved optic could produce. Backlit items further impacts the image quality



^{centre crop | 135mm f/2.8 AI @ f/2.8}

In the contrast test images above, its clear that the lens is sharp closed down a little. Its out of focus rendering is mostly nice, not objectionable but it sometimes it can feel a little nervous.



<sup>centre crop | 135mm f/2.8 AI @ f/2.8, focus at ~1.7m

135mm f/2.8 AI @ f/2.8 top | f/4.0 middle | f/5.6 bottom</sup>

So what

Consiering just the 135mm focal length alone, I've used the 105mm f/2.5 AI-S for a number of years on my DSLRs and I think I'd prefer that to a perfect Nikkor 135mm f/2.8: I think the 105mm's bokeh rendition is (subjectively) better but its not as night-day as some online forums would have you believe, the 105mm its a little lighter and more compact, and less shooting distance for headshots is required. However, the extra reach of the 135mm in a compact form would be a positive for the 135mm if you wanted a longer telephoto and not the extra weight of a 180mm or 200mm AI/AI-S prime (we're ignoring the 70-200mm type zoom of course)

As with most Nikkor AI/AI-S, the construction of the lens is nice and this 135mm is relatively easy to disassemble to clean if absolutely required.

Whilst this particular lens is clearly not perfect and we can clearly see the image quality affected, its clear that one in better condition would have been a nice lens in the bag if someone wanted this focal length: its reasonably light and sharp, with some decent out of focus rendering and handles very nicely particularlly the 270 degree focus throw. Obviously my copy is hindered by the terrible state of the front element that gives the soft focus look, but even if you could shoot it this way for a Holga-like experience it certainly not as your main rig so when considering lenses with similar compromised front elements we have an idea of what we're getting ourselves into.