ZUNOW 5cm F1.1:

By Kenneth Min Zee · Updated October, 2026

History, Variations and an Ongoing Investigation

The ZUNOW 5cm F1.1 is one of the most remarkable Japanese rangefinder lenses of the 1950s.

At the time, producing a compact normal lens with an aperture of F1.1 was an extraordinary optical challenge. Surviving examples show considerably more variation than is sometimes suggested by simple production lists.

My collection currently includes five ZUNOW 5cm F1.1 lenses, representing different mount, casing, and production variations. In addition, I own three ZUNOW Elmo Cine F1.1 lenses with focal lengths of 6.5mm, 13mm, and 38mm, bringing my total ZUNOW collection to eight lenses.

The more lenses I examine, the more interesting the story becomes.

This page summarizes what I currently believe can be established with reasonable confidence — and also identifies the questions that remain open.

The Rear-Protruding “Ping-Pong” ZUNOW

The most distinctive ZUNOW configuration is the version with the large rounded rear optical housing.

Collectors commonly refer to this as the “Ping-Pong” ZUNOW.

The earliest examples use this protruding rear construction, and the early optical system is generally described as a nine-element, five-group design.

Its construction was extraordinarily ambitious for the period, especially considering the challenge of producing a compact F1.1 rangefinder lens using the optical materials and manufacturing methods available in 1950s Japan.

However, one important point has become clear from examining more surviving examples:

Ping-Pong construction is not limited to only one external casing style.

There are early-casing Ping-Pong lenses, but there are also later-casing lenses which still retain the protruding Ping-Pong rear optical assembly.

This means that a simple classification such as:

Type 1 = Ping-Pong
Type 2 = flat rear

does not describe every surviving lens accurately.

The external casing and the rear optical configuration appear to have evolved separately.

Ping-Pong ZUNOW Examples

Zunow 5cm F1.1 Type 1 set up had 9 elements

One particularly useful reference lens is serial No. 6136.

No. 6136 has the later-style casing but retains the pronounced Ping-Pong rear optical assembly.

For my own research notes, I describe this as a later-casing, or “Type 2,” Ping-Pong configuration.

This example is important because it demonstrates that the change in casing did not necessarily coincide with the disappearance of the Ping-Pong rear construction.

The Flat-Rear ZUNOW

Another major configuration uses a much flatter rear construction.

This later optical system is generally described as an eight-element, five-group design.

The change appears to represent a substantial development of the original concept, but I am cautious about claiming a single reason for the redesign.

Improved aberration correction, manufacturing consistency, mechanical packaging and practical usability may all have contributed.

The important point is that casing development and rear optical development should not necessarily be treated as the same event.

Flat-Rear ZUNOW Examples

Factory Modification Complicates the Story

One lens in my own collection is particularly important to this research.

Serial No. 5313 is presently in a flat-rear configuration.

According to the previous owner's family, however, the lens originally had the Ping-Pong rear configuration and was later returned to ZUNOW, where it was modified.

If this history is correct, it demonstrates something very important:

The present appearance of a surviving ZUNOW does not necessarily tell us exactly how that lens originally left the factory.

An early serial number with a later-looking rear assembly is therefore not automatically a modern hybrid or an incorrect lens.

It may represent historical factory modification.

At the same time, repairs and parts replacement over roughly seventy years mean that unusual surviving examples must be examined carefully.

For this reason, provenance is becoming almost as important as serial number.

Teikoku Kogaku vs. Zunow Opt. Japan — The Evolution of Lens Engravings

Surviving lenses also show changes in company markings.

Earlier examples can carry Teikoku Kogaku engravings, while later examples are marked Zunow Opt. Japan.

These markings are useful chronological clues, but they should not be interpreted by themselves.

For serious comparison, I try to examine several characteristics together:

serial number
mount
casing
rear construction
front engraving
company marking
aperture operation
filter thread
provenance

No single characteristic tells the complete story.

Old and New LTM Casing Styles

Surviving LTM versions of the ZUNOW 5cm F1.1 show at least two clearly different external casing styles.

For my research notes, I refer to these simply as:

Old LTM casing (OL)
New LTM casing (NL)

The distinction is based on the overall barrel construction rather than serial number alone.

The main identifying features include the shape and proportion of the stepped barrel sections, the construction around the aperture ring, and the form of the central cylindrical body.

Importantly, OL and NL should not be interpreted as a simple chronological sequence.

The surviving examples documented so far show that Old and New casing styles overlap within the serial-number range, and Old-style LTM casings can still be found among 6000-series lenses.

This means the production history cannot be explained simply as:

Old → New

Aperture operating direction is therefore recorded separately from casing style.

In my working notation:

OL-R = Old LTM casing / aperture opens to the right
OL-L = Old LTM casing / aperture opens to the left
NL-R = New LTM casing / aperture opens to the right
NL-L = New LTM casing / aperture opens to the left

Keeping these characteristics separate helps avoid treating casing style, serial number and aperture direction as a single production sequence.

S-Mount Variations: Nikon, Contax and Unmarked Examples

Surviving S-mount versions of the ZUNOW 5cm F1.1 show several identifiable variations.

For my research notes, I record the mount family first, followed by aperture operating direction and, where applicable, the specific Nikon or Contax marking.

If no Nikon “N” or Contax “C” marking is present, I classify the lens simply as:

S-L = S-mount / aperture opens to the left
S-R = S-mount / aperture opens to the right

Where the mount is clearly identified by an engraved or painted Nikon or Contax mark, I add that designation:

S-L Nikon
S-R Nikon
S-L Contax
S-R Contax

Black-finish S-mount examples are recorded with an additional B:

SB-L
SB-R
SB-L Nikon
SB-R Nikon

Other distinctive markings can also be added where useful. For example:

S-L EP = S-mount / aperture opens left / EP-marked variant

This notation is intended as a practical research system rather than a factory designation.

It allows mount type, finish, aperture direction and special markings to be recorded separately without assuming that any one feature defines the production sequence.

My ZUNOW Collection — Eight Rare Lenses

My collection currently consists of eight ZUNOW lenses: five examples of the legendary ZUNOW 5cm F1.1, comprising two Leica screw-mount versions, two Nikon S-mount versions, and one exceptionally rare Eyemo-mounted example (No. 3570).

In addition, I own three ZUNOW Elmo Cine F1.1 lenses with focal lengths of 6.5mm, 13mm, and 38mm.

Together, these eight lenses represent two fascinating aspects of ZUNOW's optical heritage: high-speed rangefinder photography and specialized motion-picture optics.

The three Elmo Cine lenses will also provide an interesting foundation for OLJ Project D, which explores adapting historic cine lenses for modern digital photography.

My Five ZUNOW 5cm F1.1 Lenses

I am not interested only in displaying these lenses.

I use them.

My five ZUNOW 5cm F1.1 lenses represent several different mechanical and production variations,

including Leica thread mount, S-mount and Eyemo-mount examples.

Having the actual lenses side by side allows me to compare casing construction, aperture operation,

engravings, filter threads and rear assemblies directly.

That practical experience is important to me because optical history becomes much more meaningful when the lens is actually mounted on a camera and photographed with.

The 54.5mm and 55mm Question

The unusual filter-thread sizes have become one of the more unexpected parts of this research.

Among my own ZUNOW 5cm F1.1 lenses, 54.5mm is the most commonly encountered front-thread size.

My Eyemo-mount No. 3570 is confirmed at 54.5mm, as are several of my rangefinder examples.

Serial No. 5313 is unusual in using a 55mm front thread.

Initially, this raised the possibility that 55mm represented an earlier specification and that ZUNOW later changed to 54.5mm.

The surviving evidence no longer supports such a simple conclusion.

Serial No. 6136, the later-casing Ping-Pong example described above, has been personally confirmed by its owner as using a 54.5mm filter thread.

Photographs also show a 54.5mm Tiffen filter mounted on the lens.

This establishes an important point:

Ping-Pong construction does not automatically mean 55mm.

It also demonstrates that a later-casing Ping-Pong lens can use the 54.5mm thread.

The reason for the 54.5mm / 55mm difference remains unresolved.

The Mystery of “S-ZUNOW”

Some surviving lenses are engraved S-ZUNOW.

On certain examples, the letter S is highlighted in red.

The marking itself is unquestionably genuine.

Its exact meaning, however, remains uncertain.

Possible explanations have included a special specification, selected quality, export designation or another internal production distinction.

At present, I have not found documentary evidence strong enough to choose between these explanations.

So for now:

FACT: S-ZUNOW-marked lenses exist.

UNKNOWN: What the “S” officially represented.

A plausible explanation should not be presented as historical fact until supporting evidence is found.

Serial Numbers and the Surviving-Lens Record

I have been building a photographic registry of surviving ZUNOW 5cm F1.1 lenses.

The current working database contains approximately sixty photo-backed examples.

Wherever possible, I try to connect the serial number directly with photographs showing the lens, mount, engravings and physical construction.

This is important because internet photographs are frequently reposted, separated from their original

descriptions or associated with incorrect information.

For research purposes, I give much more weight to an example where I can confirm:

serial number + photograph + mount + casing + engraving + physical configuration

than to a serial number appearing only in a secondary list.

Clear patterns are beginning to emerge.

However, I do not believe the available evidence yet justifies calculating an exact production quantity simply from the surviving serial-number range.

Serial numbers may not have been completely continuous, and production may have been divided between different mounts or batches.

For that reason, I prefer not to state a precise production figure until stronger evidence is available.

The complete working database will remain private while the research continues.

Original Lenses, Repairs and Hybrids

These lenses were produced in an era when very fast optics required considerable hand assembly and individual adjustment.

Over the following seventy years, lenses have also been repaired, rebuilt and serviced.

Front assemblies, rear sections, focusing mounts and optical parts may have been changed.

An unusual configuration therefore requires caution.

It does not automatically represent an undocumented factory version.

But neither does it automatically mean something improper has occurred.

It may simply be the result of historical repair or factory modification.

With a lens this rare, provenance matters almost as much as serial number.

This is also why I strongly prefer preserving original parts whenever possible.

The ZUNOW 5cm F1.3 Mystery

My research has recently expanded to include the much rarer ZUNOW 5cm F1.3.

At first I regarded the F1.3 simply as another ZUNOW variation.

I now think the relationship between the F1.1 and F1.3 may be considerably more interesting.

Published optical diagrams associated with the F1.1 and F1.3 appear remarkably similar.

Surviving F1.3 examples also appear strongly concentrated in the 7000-series.

Examples currently recorded in my research include:

7035
7074
7119
7120
7121
7130

This clustering is difficult to ignore.

It suggests that the F1.3 was being produced or designated systematically rather than appearing randomly among earlier F1.1 lenses.

Was the F1.3 a Separate Lens — or a Production Grade?

This leads to one of my current working hypotheses.

WORKING HYPOTHESIS

The ZUNOW 5cm F1.3 may have shared essentially the same basic optical design as the F1.1, with certain lenses sold as F1.3 because they did not meet a specification required for the F1.1 designation.

In modern manufacturing terminology, this might be described as grading or binning.

Such an explanation could potentially account for:

the apparent similarity of the optical designs;
the concentration of surviving F1.3 serial numbers;
the historical price difference between the two versions;
and the existence of two extremely similar ultra-fast normal lenses.

However, this theory is not yet proven.

There may be other explanations:

The effective aperture could have been deliberately restricted.
Glass selection or spacing could differ.
Transmission could differ.
Mechanical construction could differ.
Or future documentary evidence may provide a completely different explanation.

I have now secured a ZUNOW 5cm F1.3 for direct examination and intend to compare it closely with my F1.1 lenses.

That should provide another important piece of evidence.

Facts, Observations and Working Hypotheses

Facts / Physically Confirmed

ZUNOW 5cm F1.1 lenses exist in multiple mounts and mechanical configurations.
Ping-Pong and flat-rear configurations both exist.
Ping-Pong construction occurs with more than one casing style.
Teikoku Kogaku and Zunow Opt. markings both exist.
S-ZUNOW-marked lenses exist.
54.5mm filter threads are confirmed on several surviving examples.
Serial No. 6136 is a later-casing Ping-Pong example with a confirmed 54.5mm thread.
Serial No. 5313 presently has a confirmed 55mm thread.
No. 5313 has a known history of modification.
Aperture operating direction is not identical on all examples.
F1.3 lenses are strongly represented in the 7000-series.
Some surviving lenses have been modified during their working lives.

Observations

Casing development and rear-construction development do not appear to have occurred as one simple change.
Serial number alone cannot safely identify every lens's original configuration.
Filter-thread size does not currently appear to follow a simple early-versus-late progression.
The F1.3 serial numbers appear strongly clustered.
Photo-backed examples are considerably more useful for research than text-only serial references.

Working Hypotheses

The F1.3 may have been a graded derivative of the F1.1.
Some variations between F1.1 examples may reflect hand fitting and individual adjustment.
The S in S-ZUNOW probably indicates some intentional production distinction, although its meaning remains unknown.
The 54.5mm / 55mm difference may reflect a manufacturing, assembly, service or production variation that has not yet been identified.
The present 55mm configuration of No. 5313 may be historically significant, but more evidence is required before determining what it represents.

These are working theories.

They may change when better evidence appears.

Why I Continue to Research the ZUNOW

I began researching the ZUNOW because I enjoy using the lens.

It has gradually become something much larger.

Having several actual lenses in front of me has shown how much information can be lost when vintage-lens history is reconstructed only from auction descriptions or copied serial lists.

My approach is therefore simple:

Start with the lenses themselves.

Photographs.

Serial numbers.

Engravings.

Mechanical construction.

Provenance.

And actual photographic use.

When something can be physically established, I call it a fact.

When a pattern repeatedly appears in surviving examples, I call it an observation.

And when I have an explanation that might fit the evidence, I call it a hypothesis.

The ZUNOW story is still developing.

So is this page.

A more detailed study of the ZUNOW 5cm F1.1 and F1.3 — including production variations, detailed comparison photographs and the evidence behind these theories — is currently being prepared.

Old lenses are made to be used.

View Zunow Photos