Japanese External Reverse Porro Prism Binoculars. VIRTUAL MUSEUM

My experience in buying upwards of 600 pairs of these small Japanese binoculars has been that most needed repairs, regardless of seller’s claims of functionality. The main issue is age hardened optical grease. Most of these binoculars are now between 33 to 63 years old. Oculars commonly seize on independent focus models, and then the ocular barrels unscrew. Similarly, the right ocular and to a lesser degree the focus wheel tends to seize on center focus models. Most binoculars seize at infinity, so the owners may not really be aware of it. I was recently surprised when I received 5 binoculars in a row that were fully functional. But they were quickly followed by 5 in a row that needed repair. In addition to seized oculars, displaced prisms resulting in double images (collimation issues) are not uncommon. So are dirty lenses and prisms, and missing or loose screws. I now normally assume all miniature binoculars will need work. In repairing hundreds I have developed methods that allowed me to repair virtually all of my miniature binoculars to a functional state that satisfies me. So I will share my procedures. I continue to repair 4 or 5 binoculars a week, and occasionally also repair full size binoculars for my collections. I only undertake repairs for the collections, not in commerce, and my average repair time is probably 15-20 minutes. If you are hopeless at mechanical repairs, or analyzing how things work or go together, or if you can’t manipulate fairly small items like pins and needles, then you probably will not be capable of the precision mechanical work involved in repairing miniature binoculars. But the methodology for basic repairs is really not too complicated. You do need to acquire some specific tools. For example you must have a good assorted set of flat bladed “jewelers” screwdrivers with hardened blades. Yes I do own several $100 sets of Starrett® machinist’s jewelers screwdrivers. But the cheap $8 Asian sets also work OK. You need the smaller sizes in flat blade (only) with perfect blades: not rounded; not bent; not twisted; not chewed up. The screws on these binoculars are tiny and have often been in place for nearly 60 years. They are surprisingly cooperative, but only for screwdriver blades that are a perfect fit. If not, you will destroy the slot and will not be unable to remove the screw or part. As soon as a screwdriver is damaged a little, throw it out. Some of my jewelers screwdrivers seem to have magnetized themselves. Sometimes I like that, sometimes not. Tool demagnitizers cost about $5. You will need tweezers with small ends, or jewelers screw starters, because these screws and especially the set screws are very small and you must orient them precisely back into their threaded holes if you remove them. You probably need a hobby grade lighted magnifying headset with a focal distance of around 6-12 inches so you can see what you are doing. Otherwise you can’t see what is going on with the screwdriver slots. The $300 surgical/dental type is not required. And if you are going to multitask (as in repairing binoculars while watching TV) then get a tray to work over. The tiny screws will drop all the time. They can be nearly impossible to find in your clothing/lap/chair/ rug, even with a magnet. 33 BIS 63 Jähriges verhärtetes optisches Fett ist ein häufiges Problem mit Miniaturfernglasern. Das Ergebnis ist gefrorenes Okular oder ittelfokusmechanismus. Unangepasste Prismen schaffen ein Geisterbild, und dieses ist ein allgemeines Problem. Schmutzige Linsen und Prismen sind auch ein allgemeines Problem.   Eingekerbte Prismen werden manchmal gefunden. La graisse durcie pendant 33 à 63 ans est un problème commun. Le résultat est   une oculaire saisi. Les prismes déréglés créent une image double. Les lentilles et les prismes sales sont les problèmes communs. Tout peuvent être réparé avec un peu d'effort et d’habilite. On trouve parfois des prismes griffes.





























































  - MISC





You need a set of “jewelers” flat blade screw drivers. These are high quality ones.

You can’t successfully manipulate miniscule fasteners if you can’t see the slots properly. The answer, known to jewelers and the medical professions, is a lighted magnifying headset. I have pictured examples of the extremes available. On the left is an inexpensive hobby grade ENKAY™ brand magnifying lighted headset that I used for a number of years. The light wasn’t so good so I attached an LED light bar with Velcro as an upgrade.   A better friend than I might deserve who is a dentist then gave me one of his spare pairs of top end Swiss made Sandy Grendel titanium magnifying loupe headsets to use on an extended loan basis. WOW! A couple grand more makes a big difference. There are in between choices on Ebay. Pay attention to magnification and light and work distance.

The 50’s & 60’s optical grease seizes solid, so you will need a butane pencil torch. Nothing else will do the task.

Do not use plumbing propane torches, blowtorches, or acetylene torches !! Those have far too much heat and are not precise enough. Pencil torches are not always cooperative, or reliable, so to insure you will have a working one, I suggest buying several, with the strategy that at least one will work when you want it to. You will also need a can of butane lighter fuel, and something to light the pencil torches. I use refillable BBQ lighters, but a cigarette lighter or match   works OK.

To unscrew the ocular barrels without crushing them or gouging them ( never use pliers or vise grips) you need something special. And the rubber strap wrenches don’t work well on anything this small. So you will need something like what I made above. I MIG welded steel rods to 1/4 inch automotive stainless worm gear hose clamps to use as handles. Brazing and silver soldering might also work. I ruined a couple getting 2 good ones. These look ugly but work great. They have an astonishing amount of precise grip that is very incremental and doesn’t damage the barrels. These are worth any extra effort to make, or to have someone make for you. Make 2 or more. They may look crude, but nothing I know of works nearly as well.

I find these small special shaped Irwin ®Vise Grips® handy when you can almost turn something by hand, but not quite. I don’t usually use the locking action. This tool has smooth jaws.

You’ll need a small hobby wire brush to scrub the old hard rubbery optical grease off the ocular threads.


Canned air or duster to blow specks and hairs off the lenses can be handy.

This famous name lens cleaner in handy spray bottles of a nice size impressed me with their colorful decal and famous name. It works well enough too. So I bought a whole case of it. A much cheaper alternative is the home recipe for bulk eyeglass & optics cleaner. Mix up a formula of 75% rubbing alcohol, 25% water, and 2 drops of liquid dish soap. When using any cleaner, use only enough to dampen your cotton swabs. You’ll want cotton swabs for cleaning. Cotton won’t scratch, paper products are made of wood and will. These cotton swabs do leave behind strands.

Diagnostic Tips for Repairing Miniature Binoculars. Diagnosemethoden für Miniaturferngläser. Méthodes Diagnostiques Pour la Réparathion de Jumelles Miniatures. Советы по диагностике миниатюрные бинокль. ミニチュア双眼鏡を修復するための診断のヒント. Consejos Para el Diagnóstico de la Reparación Los Prismáticos en Miniatura. Punte Diagnostici per la Riparazione del Binocoli in Miniatura.

Optical Condition of Miniature Binoculars. Zustand Von Optik der Miniatur-Ferngläser. État de L'optique des Jumelles Miniatures. птический состояние. Condición Óptica de Prismaticos en Miniatura.. Condizione Ottiche dei Binocoli in Miniatura.

Assessing Optical Quality. Bestimmung der Optischen Qualität. Determination de la Qualité Optique. Оценка качества оптических. 光学品質 の評価\\. Evaluar Calidad óptica. Valutazione della Qualità Ottica.

  An accepted method of comparing the relative optical quality between binoculars is to observe a star at night through one eyepiece. Binoculars with better quality optics will have less astigmatism, that is, they will allow a sharper focus with less hazing, blurring, or rays around the star when it is in the center of the field of vision, as compared to poorer quality binoculars. This is a comparative evaluation: your evaluation result is that binocular A is better and binocular B is worse( Neither binocular may be particularly good ). Next shift the binoculars so that the star is moved to the edge of the field of view. Binoculars with better quality optics will have less image change across the field of view, or loss of focus, as compared to poorer quality binoculars. And they will have less halo effect.

Sharp, so Better


Still sharp, so Better


Shake & Rattle. Erch ϋ tterung und Geklapper. Secousez et Faites S’entrechoquer. Шумный езакрепленные Детали. ると揺れる. Agitar y Traqueteo. Agitare e Battere.

Shake it and it rattles? Pretty good fun for babies. Less good for binoculars. It means parts are loose somewhere, and they shouldn’t be. With these miniature binoculars the most likely cause of rattles seems to be one of the four prisms being loose, or a non captive prism spring. This forewarns future collimation issues and prism damage. The cure is to tighten any loose prism adjuster screws and or reset the prisms. Note: use great restraint on these tiny set screws !!!   One wants to “snug” and not “crank down”. Over-tightening will tear the slot off the set screw or will hopelessly round it, or will chip the prism. (note the use of the word “will” and not the word “may”). Be aware that collimating the binoculars may be required after moving set screws. Another likely rattle source is a loose diopter ring, cured by tightening the 3 set screws. Be circumspect about the amount of force you use on these also. Loose lenses in the diopter or in the objective lens pack are another possible source of rattles, though in my experience, they are less commonly encountered, or noticed (even if a bit loose they rattle less). Threaded rings hold these lenses in place. If the rings are loose, they can usually be moved with the fingers or fingernail, or walked in with care using a jewelers screwdriver to push the ring around by its slot. Or make a proper tool of sheet metal. Only tighten to the point of being “snug”.

Die   von Geräuschen verursacht durch lose teile in den Miniaturferngläsern: lose Prismen, loser Diopterfokus schellt oder löst linsen.

Les bruits lâches dans les jumelles miniatures sont crees par les prismes lâches, les anneaux de dioptrie lâches, ou les lentilles lâches.

Наиболее распространенные причины плохо закрепленных деталей шумы в миниатюре бинокль: ослабление призм, ослабление диоптрии кольца, или ослабленных объективов.

Las razones más comunes para piezas sueltas ruido en miniatura binoculares: flojo dioptrías prismas, anillos, o flojo lentes.

A loose prism is a common cause of rattles. There are 4.

A loose diopter ring is a another common cause of rattles.

A less common source of rattles is loose lenses in the diopter assembly. A capture ring (A) screws in to hold the lenses.

A less common source of rattles is loose lenses in the objective lens assembly. A capture ring (A) screws into the inside of the objective barrel to hold the lens. It is usually   under a beauty ring (B) that screws onto the outside of the barrel (C).

Dirt & Specks &Haze

Haze & Fungus


Good Rattles

Bad Rattles

If you intend to take apart center focus binocular models, be aware that the center hinge screw needs a wider than normal but quite thin slotted blade. You won’t have a proper screwdriver in the kitchen drawer. A blade thin enough to fit the slot won’t be wide enough. A set such as this excellent Brownells® gunsmith screwdriver set can provide the proper size. Or you may be able to modify something like a putty knife by grinding it.  

Improvised Replacement Eyecups. Ersatz Augenschild.   Boucliers   d’oeil Improvisés de Rechange. Improviserade Ögonmussla. Improvisados Anteojeras Prismáticos.

Eyecups on these small binoculars are frequently lost. Eyeglass wearers sometimes remove them. Or the threads strip (common on the all-plastic eyecups). Since replacement eyecups were never available, one sometimes encounters home machined replacements in Delrin®, other plastics meant for machining, or aluminum or brass. A person with machinist skills, access to a lathe, and an abundance of free time can do this. But to put it in perspective, I do have a lathe, do have Delrin® and aluminum and brass rod of a suitable size, have a bunch of miniature binoculars that need eyecups, but I never quite felt it was worth my time or effort to make eyecups. Anyway, some of these home made replacement eyecups can be rather interesting.

My Binocular Parts Game. Ein Spiel Mit Gefallenen Fernglas Schrauben. Un Jeu Avec les Pièces Jumelles Laissées Tomber. Игры поиск сбросили бинокли детали. Un Juego con Pequeñas Piezas Prismáticos.

I often play an interactive binocular game. I seem to play it a lot. It can be addictive. You too can play. See if you can find the binocular prism adjusting screw and prism cover screw in the (messy) carpet. Yes I know I have been derelict in using the vacuum. I have 9 Dyson® vacuums. Went to a Yale U. lecture by the inventor. Obviously doesn’t motivate actually vacuuming much. But I probably look good when I wheel the colorful machines about, and with good suction they are probably full of small binocular parts. Hint # 1: If you can see something in both photos in the same place, it isn’t either of the screws: only one screw is in each picture. Hint # 2: If it is fairly easy to spot, then you know for a certainty that it is not the screw. They are never easy to spot. Hint #3: the arrows point to the picture, not the screw location.   Disclosure: Right after I took the photos I could spot each screw in the photos (knew where they were) so I know the screw is actually present in the designated photo. I forgot where to look and can’t find them now... Just like real life.

Neko thinks this game is way lame!

I can’t argue that point.

She says you can never spot the screw no matter how much time you spend trying.

I can’t argue that point either.

That’s what makes it so realistic, it is just like repairing binoculars.

(so I rely on magnets and a high power crime scene UV flashlight to help find dropped screws, and work over a tray to catch errant screws.)

Binoculars Damaged From Being Dropped.

                                                  Tropfenschaden auf Ferngläsern.
                                                  Dommages D’impact des Jumelles.
                                                  Ущерб от падения Бинокль. 
                                                  Prismáticos Dañado Por se Dejó Caer al Suelo.

It is not uncommon for binoculars to display damage from being dropped. Impacts can chip a prism or objective lens, or knock an objective lens barrel loose from its threads and seize it. But even some fairly dramatic damage from being dropped may be merely cosmetic. Most objective lens barrels have an extension beyond the objective lens that functions both as a sun shield and as a crush space before any impact affects the lens. Most objective barrels are soft aluminum. Dropped binoculars do commonly require realigning the prisms. And the damage often signals general abuse that may extend to other aspects (like scratched lenses and dirty internal parts).

1920’s Optistar with drop damage. These are remarkably tough and well made little binoculars: the hard drop didn’t even knock the prisms out of alignment. I’ll probably try to round out the damage a bit sometime, using the method below.

The owners of these binoculars apparently confused them with a   rubber bouncy ball. They display evidence of at least 6 or 7 drops. Think “demolition derby” for binoculars.  

Impact damage to a prism cover. There are good air spaces inside, so dents do not necessarily impact the prism directly. A drop can cause a prism adjusting screw to spall the prism, however. Always look backwards (into the objective lens and out the eyepiece) to see internal binocular problems you may not see when you look through them normally.

Drop damage on the objective lens barrel, the most common binocular impact damage.

Improving a damaged out of round binocular objective barrel end can be accomplished by finding a hunk of round material stronger than the soft aluminum or brass of the objective barrel, cutting into a form, and then using a pinching motion to re-form the desired shape. Some possible donor materials might be steel EMT conduit and couplers, PVC plumbing pipe and couplers, steel tubing and such. Or for the larger sizes: perhaps auto exhaust tubing and reducers, or U shaped muffler clamps. Use some initiative and imagination as potential donor tube material is everywhere. One wants a size and curvature that is similar, but it does not really need to be exact. Split and trim it with a hack saw or band saw into a handy size. For the pinching tool I like to wrap some electrical tape around one jaw of some Needle Nose Vise Grips® which covers the serrations and gives a more rounded and gentle action. I think they give good leverage and good force and control. (Needle nose only).

      (My) Theory of Repair

—Keep it simple, logical, cheap.

—Apply economy of effort.

—Get a (quite good) result that is all

    out of proportion to the above.

Grips with jaw padded with electrical tape

To illustrate the method, I grabbed the abused Diamond 12 x 50 binoculars illustrated above left. A few minutes rummaging in the barn turned up two items with an appropriate diameter to use as a form: a Land Rover truck exhaust hanger and a universal muffler clamp. Smaller binoculars might require cutting pipe, or tubing. A trip to a good hardware store with the binoculars should turn up something usable.

Before Picture… this is just sad !!

After investing 5 minutes of indifferent effort.

Shift binoculars so the star is moved to the edge of the field of view.

Observe a star through one eyepiece.

Halos on angels? Probably good.

Halos on   binocular images? Not so much.

Neat small screw starter gizmo, shown around life size. This makes getting the hidden prism cover screw started an easy task. This flea market/boot sale find was probably a watchmaker’s tool.

Tools You Will Need to Repair Miniature Binoculars. Werkzeuge, die Sie Benōtigen um Miniatur-ferngläser zu Reparieren. Outils don't vous Aurez pour Réparer des Jumelles Minatures. Инструменты, необходимые для восстановления миниатюрных биноклей. Verktg du Behöver Reparera Miniatyrkikare. Las Herramientas que Necesitará Para Reparer los Prismáticos en Miniatura. Strumenti Necessari per Riparare I Binocoli in Miniatura.

Can you find the binocular screw?

Können Sie die fernglas Schraube finden?

Pouvez-vous trouver la vis des jumelles?

Вы можете найти бинокли винта?

Look backwards through the binoculars.

Schauen Sie durch die Ferngläser in umgekehrten.

Regardez par les jumelles d'une façon inverse

Смотреть через бинокль в положении заднего хода

Rattlesnake, image by Tigerhawkvok, used under the Creative Commons Attribution ShareAlike 3.0 License

This simple binocular repair using my technique of pliers against a rounded form only required 5 minutes to achieve a dramatic improvement in appearance.


Einfache fernglas reparatur mit großen ergebnissen. Unter Verwendung meiner technik der anwendung von zangen und von gerundeten form, dauerte es nur 5 minuten, um eine drastische verbesserung dem aussehen nach fernglas


La réparation simple avec des bons résultats. Utilisez ma technique: employer des pinces d’une forme arrondie, 5 minutes pour obtenir une amélioration formidable.


  Простой бинокли ремонт. С помощью метода с помощью щипцов и закругленными шаблона, его только 5 минут, чтобы получить существенное улучшение внешнего вида.


Plus Mauvais

Besseres, Meilleur  


Plus Mauvais





  Vorher, Avant, До

  Nachher, Ensuite, после

To judge the condition of the lenses and prisms, look backwards through the objective lens of the binoculars, as shown. Internal dirt, specks, haze, fungus, and lens or prism chips will be more easily seen. Fungus is a live growing organism that feeds on dust, and you see the mycelium tendris (feeder roots). They excrete digestive acid that can etch the lenses and prisms. Unlike dirt, specks and haze, fungus cannot necessarily be cleaned off, and may represent permanent damage. Leitz documents   suggest a fungus treatment of 94% distilled water, 4% clear ammonia (for cleansing) and 2% hydrogen peroxide (to kill the fungus).  

After a couple years of scratching around in frustration in the bottom of a box every time I needed a screwdriver of a certain size, I spent around 15 minutes with a drill modifying   this wooden box into a custom binocular repair tool box. I think it works very well...and with negligible cost and a reward all out of proportion to effort... what’s not to like?  

A robotic helping hand might be nice...

A box full of miniature binoculars “only good for parts” is handy, and is needed if replacing parts, but is not really needed for many basic remedial repairs.

Model car tire eyecup

Photo courtesy of Trent

“Aircraft” Soft jaw pliers can be handy to remove objective barrels. These are   Snap-On ® part number PCW52a. Other companies make similar tools. Good controllable grip and leverage without damage. I spent lots of money on lots of Snap-On® tools in the past. But the company had a defective plastic compound they used in their plastic handled tools (their engineering dept confirmed this to me in writing) that causes the plastic to eventually crumble.

Cloud Callout:

...and I smell some haze and fungus on the ocular lenses...

ALMOST scientific methodology...using a CAT.

Cloud Callout:

… and I hear a worrisome rattle in the objective side right hand prism cover...

ALMOST scientific methodology...using a CAT.


Ich höre ein Prisma schütteln

  J'entends un prisme secouer

Я слышу сквозь призму встряхните

Escucho un prisma agitar


Ich kann riechen optische pilzbefall

  Je peux épeler optique la croissance fongique

  Я может запах оптический грибков

  Puedo olerlo crecimiento de los hongos óptico


Mini Fernglas Reparatur: Was wird benötigt?

Pouvez-vous réparer miniature jumelles?

  Вы можете сделать ремонт миниатюрные бинокль?

¿Puede reparar miniatura binoculares?


Chipped lens or prism

Text Box:

Fungus often assumes a snowflake crystal appearance. Bad stuff.


PB Blaster® is unmatched in freeing up seized parts, though not ones with hardened optical grease. Keep away from lenses.

93% alcohol is handy for general cleaning.