The final pancake - the plastic 50mm f/1.8 AI-S pancake

The final 50mm f/1.8 AI-S manual focus lens, with its 0.6m minimum focus distance and missing rabbit ear/coupling prong, was a lens that was following the times and a shift away from previous Nikkors and their mostly metal construction. Whilst there was an earlier 50mm f/1.8 AI-S pancake which could focus down to 0.45m like the long nose version, that version was only available in Japan and short lived whereas this 50mm pancake superceded both the Japanese pancake and the long nose. Identifying the latter pancake can be done via the serial numbers (starting 4xxxxxxx) and the distinct shiney plastic-ness, particularly of the aperture ring and the additional bump on chrome index/grab ring - this bump was supposedly to help users to quickly orientate the lens, given the missing rabbit ears of earlier AI/AI-S lenses.



So what's this pancake like?

^{Throughout the rest of this post, I'll use 50mm pancake to refer to the final 4xxxxxxx serial number version of the Nikkor 50mm f/1.8 AI-S with the 0.6m focus distance}

The Series-E pancake

The 50mm pancake also had a cost-cutting Series-E cousin, sold under the "Nikon" name rather than "Nikkor". Nowadays the 2 pancakes seem get close although not on par to sale prices on the second hand online market but the Serie-E is reportedly even more plastic-y. For the latter chrome index ring Series-E version, a quick glance can mistake the for the Nikkor pancake with online sellers also makeing/leveraging this mistake.

So its is a little difficult to determine what are the key differences between this pancake and the Series-E pancake. Interestingly Nikon themselves note that the optical formula is shared for both the 50mm pancake and the Series-E:

I. The Nikon EM and Series E Lenses

.. the Series E 50mm f/1.8, sold in some regions including the U.S., and the AI Nikkor 50mm f/1.8S were actually sister lenses designed with the same basic optics, but different outward appearance and coatings.

Indeed, when the Nikkor and Series-E pancakes are opened, they are very similar - the earlier Japan market Nikkor pancake with serial numbers 2xxxxxxx however is mechanically (and optically) different.

This pancake

I've seen a number of the 50mm pancakes over the years - some in decent condition but also a number in junk shops in absolutely terrible condition: fungus etched/scratched elements/damanged bodies etc. My current copy had the focus helicoids mistakenly separated and other mechanical issues as well as some minor etching on the rear element from previous spots of fungus: the usual hydrogen peroxide bath/ligher fluid was not able to clear it away.

Resolving these issues, particularly the helicoids issue, took a LOT of time and cross referencing to online blogs and YouTube videos for a Nikkor 50mm f/1.8 pancake with a number of dead ends given the lack of awareness of the differences in the 2x pancake versions. Ultimately I was able to fix the lens but it was defnitely not trivial.

^{Tools to open: rubber cups (not shown rubber cones to open optical blocks or lens sucker) and JIS-0 / JIS-00 drivers}

Cleaning Optical Elements

The optical strucutre of this pancake is similar to the other 50mm f/1.8 AIS lenses. The rear optical block housing sits in the main objective also includes the focus helicoids and irus and can be accessed by removing the retaining collar - you can remove this in place without removing the bayonet mount but you may need to remove it one time to add IPA to soften any seals - AVOID acetone since large parts of the housing is plastic. Once the rear retaining collar is removed the rear element plus the cemented 2 elements (seperated by a spacer) can be removed with a lens sucker.


^{(c) Nikon - 50mm f/1.8 AI-S (representavie pancake) optical cross section, front element to the left}

Front optical block and its 3 elements

The front optical block needs to be removed from the lens for effective access: unscrew the nameplate with a rubber tool to gain access to the 3x JIS-00 screws securing the metal housing that includes the filter ring. Once removed we are able to access the next 3x JIS-00 screws that secures the front optical block to the main objective containing the rear optical block. To access the front 3x elements you must go through the front and the rear of the optical block.


^{top L-R: removal of plastic nameplate, 6 screws in 2x sets of 3x (long screws secure filter fing, shorter screws secure optical block) | bottom L-R: metal filter ring and lifting front optical block (note the square notches which accept the longer screws to secure the filter ring)}

The front element is most painful to open - the seal needs to be softened to remove the front retaining collar but its tight: using a strip of rubber wrapped around the front collar and holding the rest of the optical block with a rubber cone, we can twist off/loosen the front collar enough to then use rubber cones in future. The front element can be removed with a lens sucker or gravity - the other 2 elements need to be remove via the rear. The rear element of front optical block is cemented into its retaining collar - to remove this use IPA to soften the seal and a rubber cone can be used to unscrew it and give access to the internal element.

Re-Aligning helicoids

With the front optical block removed its possible to access the helicoids which consist of the main plastic objective housing helicoid and the brass helicoid of the focus ring. The main helicoid is attached to the focus ring via 3x JIS screws - note that there are 4x screw holes on the brass helicoid: with the lens at infinity, we can observe 1x hole is located close to the infinity mark and another group of 3x holes together oppsoite. This must be the position when reassembling otherwise the plastic main objective will not be in its correct position.

When looking into the lens from above and we consider infinity at the 12o'clock position, the middle of iris spring should be at about 4o'clock.


^{Screwdriver notes infinity focus position; note the black screws securing the focus ring to the brass helicoid - group of 3 holes (1 obscured by the tab of main focus helicoid) opposite infinity position}

The helicoid keys are accessed from the rear.

If like me, you have unknown helicoid positions, you have to assemble the 2 helicoids together, along with the front optical block and then mount on camera. Given this is a methodical assemble, test, try again, you can save some time by assembling the helicoids, attaching only the rear bayonet (leaving the helicoid keys, aperture ring and focus ring) and then seating the front optical block and looking through the viewfinder. If all looks reasonable for helicoids you can reassemble with the helicoid keys and focus ring attached to test focus distances.

^{Helicoid key positions and height of plastic objective when assembled}

What worked for me was to separate both helicoids and attach the brass helicoid using the right hole of the group of 3x as my starting position - this would mate roughly at the inifinity position and would need 6.5 counter clockwise rotations so that the single hole would be roughly at inifinity position again.

The main objective/helicoid is then mated aligning the helicoid key cut-out slot to the left orange DoF indcator on the index ring. Turn the helicoid and observe the rear for correct alignment at the rear - when the helicoids are mated, ensure at the rear side of the lens, the aperture post is aligned correctly to accept the fork from the aperture ring and slightly align the helicoid key cut-outs to install the helicoid keys and this should be close.


^{(c) DIY Extravaganza 50mm pancake service YouTube - left: brass helicoid with hole groups, single hole should align with infinity mark and right most hole at inifinity used as rough mating guide | right: rough main objective mating position with cut-out slot}

I wasn't able to take photos of my exact mating positions but reference to the YouTube video above can give good hints.


^{Note the height of the rear element when helicoids aligned correctly}

^{NB: the experiences below are comparing my copy of the pancake which was previously tampered with, with optical elements reassembled incorrectly and helicoids misaligned and with minor etching of minor fungus spot to rear element.}

Handling

The primary draw of the pancake is its size to performance and cost ratio - and it is small, weighing in at ~145g and 3.2cm tall when focused a closest distance and 2.6cm when at infinity focus: comparing this to the long nose (which is relatively compact) we have ~220g and ~3.9cm at its most compact size.

The focus ring smooth but obvoiusly this will different given different condition of lenses and the plastic focus ring (not rubber) is not overly annoying but it is narrow (1 row high). The same comments apply from the long nose for the aperture ring handling - its a little narrower (2 rows: ~7mm tall) than the conventional AI-S aperture rings (3rows: ~11mm tall) but you can get used to it.


^{50mm f/1.8 AI-S pancake and long nose}

Whilst we bemoan that this pancake is more plastic-y than the other Nikkor AI-S lenses of that time period, in your hand and use its not as noticable (aside from the lack of weight) and still superior to the feel of the 50mm f/1.8D.

Sharpness

When compared to the older 50mm f/1.8 AI-S long nose - and I acknowledge the test shots are not identical - the long nose seems to be a bit sharper and have better contrast with faster handling of CA when stopping down.

^{centre crops: top: 50mm f/1.8 pancake, bottom: 50mm f/1.8 long nose @ f/1.8 - 2.0 - 2.8. Click for full size}

The long nose shows better sharpness stopped down a 1/3 to f/2.0 but the pancake continues to be a little soft but improves significantly if stopped down to f/2.8. I notice there is more veiling and CA wide at f/1.8 and f/2.0 on the pancake in the examples above - whilst the long nose also has CA wide open, it's better than the pancake.

The pancake's sharpness when eveluated on its own is not bad - wide open its soft and f/2.8 is where it really starts to get better with f/5.6 being the best in range.

^{centre crops: top - bottom: 50mm f/1.8 pancake @ f/1.8 - 2.0 - 2.8 - 4.0. Click for full size}

Bokeh

The out of focus rendering is fine although some specular highlights get odd half circle edges

<sup>f/1.8


f/2

top: f/1.8 | bottom: f/2.8</sup>

General Usage

As a walk around, using it from f/2.8 (which is the shooting aperture below unless stated) there are no real issues with the lens. I find that far distances/infinity is not perfect but this may be due to this copy's history.

At f/2.0 and wider we still get to see the slight blooming of highlights (see the London Underground lettering) - it does not always come wtih CA but CA is apparent in the usual high contrast areas and remains until after f/4 at least. Whilst our simple test above shows that the image sharpness clearly improves between f/2.8 and f/4, in general usage its not a massive problem using the wider aperture.






<sup>f/5.6 at infinity






f/1.8</sup>

Is it worth the hype

The pancake performs well, it's not an outstanding performer but its not bad. I find that, at least this copy, wide open is not overly sharp which contradicts some other review and I also find the long nose a little sharper until we get to f/5.6 and then its really splitting hairs. As with our evaluation of the other commodity Nikkor 50mm I prefer the f/1.4 AI-S overall even with its issues and this lens serves a specific market seeking a small, light and optically sufficient lens. And it is does have a novelty feel to it given the size ratio when mounted on a bigger DSLR such as a D800 - but importantly its reasonable fun to use and optically sound so there's no hesitations for enjoying this pancake.