Some maintenance notes for Leitz microscopes from the days when Leitz still was Leitz

(here covering microscopes from the period of around 1935 to 1990)

Scroll down all the way to the maintenance notes links. The notes are pdf files that can be downloaded.

Information provided

It appears that very little service information is publicly available for Leitz microscopes from the 170 and 160 mm tube length periods. Many of these 40-80 years old microscopes have now been retired from institutes and businesses and sometimes appear on the used microscopes market. Consequently, many microscope amateurs have been delighted to finally be able to afford one of these dream instruments. The microscopes were originally built to the highest standards, but today, 40 or more years later, many show signs of their age. A common and only worsening problem is that microscope controls get sluggish or even frozen due to aging grease. The only sustainable remedy is to remove the old grease and replace it with fresh grease.

Ideally microscope maintenance should be performed regularly and by authorized microscope service technicians that possess the necessary training, experience, and equipment. Microscope service is however time consuming and therefore the costs may be an obstacle for many microscopy amateurs. Furthermore, not all amateur microscopists are fortunate to live close to a professional microscope service organization, and microscope owners are generally (and with good reasons) fearful of shipping their beloved instruments. For those who realize that their microscope needs service but can’t afford professional help only one choice remains: Do-it-yourself. The maintenance notes provided here have been compiled with the hope to offer amateur microscopists some encouragement and some hints to help them to perform certain maintenance tasks on their aging Leitz microscopes.

I need to disclose that I don’t have any experience or qualifications for microscope maintenance or service. Neither do I have access to any relevant service manuals. The provided information is based on reverse engineering of a few microscopes that I have picked up. It means that the information should be perused with a critical mind. Be prepared to find errors and questionable advice.

Please report any concerns or shortcomings you may have identified (atuma[at]dccnet[dot]com).

Terminology

As much as possible I have tried to follow established microscopy terminology, but there isn't always consensus about the names of the various microscope parts. In many cases I have found it necessary to put tentative names on items, even though some of my choices may sound ridiculous in more knowledgeable ears. Refer to the images for the names used.

Collimation

Collimation is the procedure of aligning the optical axes of all optical components so they coincide into one common optical axis. The purpose is to optimize the instrument’s optical performance. On a microscope typically the following components are brought into collimation: Illumination (lamp, collector, field diaphragm), substage (condenser holder, condenser), stage, objective turret, and head. Microscope collimation is typically performed during manufacturing and after service. It is a task that requires training and special equipment (an autocollimator and supporting adapters) which unfortunately takes it beyond reach of the typical microscope amateur. Consequently, the maintenance notes provided here don’t include any true collimation instructions for the affected components, there will only be some trivial hints, admittedly not much better than “do your best to keep things straight”.

If collimation is important to you, then you should not try to service your microscope according to these maintenance notes; you should seek professional microscope service.

Screws and screwdrivers

Screws are sometimes difficult to remove because of corrosion, exposure to moisture or laboratory chemicals, or just because they have been sitting undisturbed for decades. Microscope screws typically have quite narrow drives (i.e., the slots in the screw heads into which the screwdriver tip should fit.) Using a screwdriver with a tip that doesn’t fit perfectly into the screw drive may damage the screw, and, in unfortunate cases, make the screw very difficult or impossible to remove. It may also be difficult to find good replacements for damaged screws. Therefore, it is a good idea to use high quality screwdrivers of the more expensive hollow-ground designs. These can be purchased as kits (typically for gunsmith use) containing up to some 100 bits of varying tip thicknesses and widths. The advantage of such kits is that they include many tip sizes; the disadvantage is that the handle shafts typically are quite thick and sometimes short, which makes it difficult or impossible to reach screws in more confined locations. Even with the most elaborate screwdriver kit you may find that some microscope screws still can’t be matched with a properly fitting bit. In such cases it may be necessary to reshape and modify (grind) the tips of “ordinary” off-the-shelf bits or screwdrivers. Note however that grinding may weaken the factory hardening of the tip.

Besides a perfectly fitting screwdriver the removal of a stuck screw may require considerable muscle strength. The force and exertion required to release the stuck screw makes one prone to shake and wobble with the screwdriver which may lead to slipping and damage of the screw head. To avoid such accidents 1) hold the screwdriver strictly perpendicularly to the screw head, 2) be aware of your wobbling tendencies so you can stop before you slip, 3) position yourself comfortably and with good access to the object you work with, 4) make sure that the object sits steadily fixed and is well supported, and, again, 5) use only a well-fitting screwdriver.

Dealing with stuck screws is a topic that deserves its own book. A lot of advice can be found on Internet and YouTube. Many of the suggested procedures are brutal, use them with discrimination.

Items that are stuck in threads

It is not uncommon to find that components and parts of older microscopes have become stuck in the threads. Threads get stuck for various reasons, like for example, too hard tightening, ingress of oil or other liquids that eventually harden into a resin-like substance, or corrosion. There are several ways one can try to release an object that has become stuck in its threads; however, when the object contains lenses, then the priority must be to protect the lenses from damage:

• Brute force.
  Using tools like a vise or pliers is what immediately comes to mind, but then one needs to be very careful not to damage any sensitive surfaces. Some robust protection from the vise’s jaws or the pliers’ sharp teeth is important for a happy ending. Additionally, too much gripping force applied by the vise or pliers may deform and damage the items.
• Penetrating oil.
  Commercially available penetrating oil (like WD-40 or CRC 6-56) is typically a mixture of a low-viscosity oil with a petroleum-based solvent. It is applied to the thread and left to work for some time (hours or days) before one tries to unscrew the stuck object. The danger is that the oil also is prone to creep into any adjacent optical parts and may wreak havoc by contaminating the lens surfaces and even dissolving the resins that are used to glue the lens elements.
• Knocking with a hammer.
  Use a small hammer, perhaps one with a plastic head, to knock on the stuck item to release it. Be careful to avoid damage - it’s better to use many lighter knocks rather than a few hard knocks. Also try to combine the hammer knocking with application of penetrating oil.
• Solvent treatment.
  Dipping or soaking in solvent for a few hours to several days is an efficient, albeit slow, way to release an object that is stuck in threads with hardened grease. This is of course not possible (or at least very risky) to do if the object contains lenses because the solvent most probably will find its way into the optics and wreak havoc in the same way as the penetrating oil mentioned above.
• Heating.
  Heating an object that is stuck in its threads due to hardened grease is often a quick way to soften the grease enough to be able to unscrew the object. The heating can be done in a warming cabinet or with an electric heat gun, although temperature control is more difficult with the latter. Normally one would prefer to heat the object to at least say 60°C (140°F), but this could be dangerous if lenses are involved (risk of lens delamination). In sensitive cases more moderate temperatures could be tried, like 40-50°C (100-120°F.) In difficult cases repeating the heating may help.
• Freezing.
  Putting an object with a stuck thread for a couple of hours in a freezer may help to release the thread. Similarly as for the heating approach one should be aware that temperature changes may physically damage optical parts, and freezing may also cause water vapour to condensate on the inside between the lenses. In difficult cases repeated freezing treatment may help.

Tools and other Equipment

You will need a decent collection of general tools, like pliers, tweezers, and wrenches. Some tools are affordable and ubiquitous, other are expensive or more difficult to find. Below are some tools and other equipment that I have found to be particularly useful.

• Toothpicks, wood, with pointed tips. Useful for many purposes. Advantages: Inexpensive, non-magnetic.
• Cotton swabs, various sizes (if available): Very useful for cleaning and applying oil/grease. A disadvantage is that they leave cotton fibers behind.
• Vise. Available in many sizes and designs. Use suitable jaw pads to protect any sensitive items you work with.
• Miniature (watchmaker) screwdrivers, various sizes from 0.8 mm to 2.5 mm.
• Hex (Allen) keys, metric, 1.5 to 3.0 mm in 0.5 mm increments.
• Wrenches, both adjustable and open ended.
• Adjustable face pin spanner, with replaceable pins of varying sizes up to 3 mm diameter. Very useful, even indispensable, but typically expensive.

  

• Camera lens spanner, with various, exchangeable tips. Usually affordable. Unfortunately the common pointed tips are prone to slipping.

  

• Strap wrench. Provides a good grip and torque around cylindrical and slippery surfaces. Avalable in various sizes - get the smallest you can find. Actually, get two. (The strap wrench in the image holds an eyepiece.)

  

• Jar opener, rubber lined, various designs and sizes. Provides a good grip and torque around cylindrical and slippery surfaces.

  

• Dental probe, stainless steel. Dental probes are convenient replacements for steel needles. Various models are available. Useful for many purposes.
• Digital caliper with 0.01 mm (0.0005 in) resolution. Many models are available, some surprisingly inexpensive, other very expensive. Often its cost reflects its accuracy. An accurate caliper is also useful for checking cover glass thickness when you use dry objectives with high numerical aperture.
• Solvents for cleaning and removal of oil and grease. Old and hardened grease can in most cases be removed with the help of solvents. Acetone is a very efficient solvent (and not too bad from a health perspective) but should be used with the understanding that it dissolves/deforms many plastics and paints. It is also very flammable. A convenient alternative is to use the milder (but less powerful) solvent isopropanol. Often however stronger (i.e., with better grease dissolving ability) solvents will be needed, like, for example, hexane, heptane, iso-octane, various petroleum distillates, or perhaps even xylene or toluene. White spirit*, or more exactly “a petroleum distillate with the approximate boiling point range of 150-205°C (300-400°F) including aromatic hydrocarbons”, has become my favourite grease-cleaning solvent due to its dissolving power, low volatility, ubiquity, and low cost. With any solvent, arrange for proper ventilation, protect your eyes, wear disposable nitrile gloves, remember that solvents are flammable, and be aware that some solvents may damage some plastics and paints.
  * “White spirit” is unfortunately an ambiguous name; it may be used for petroleum distillate solvents with very varying compositions and properties. You may also find it under other names, like solvent naphtha, Stoddard solvent, mineral spirits, paint thinner, etc. Only by scrutinizing the MSDS (material safety data sheet) you may be able to decipher what you’ve actually purchased.
• Glass jars, with covers (if possible), different sizes. For soaking of microscope parts and components in solvent.
• Penetrating oil. WD-40 is perhaps the most known, but there are many similar products. Penetrating oil mainly consists of solvent and oil; the solvent for fast penetration into threads and other narrow crevices, the oil to reduce friction. Penetrating oil is typically sold in a spray bottle but spraying it on a microscope is not a good idea due to a high risk for contamination of adjacent parts. A better approach is to spray it into a small bottle (with a cap so it can be stored without evaporating) and then dispense portions of it with precision using a pipette, a toothpick, or even a cotton swab. One often hears that someone has successfully managed to use penetrating oil to unfreeze equipment that has become sluggish due to old grease. This approach may sometimes work but it is questionable as a long-term solution. The solvent will soon evaporate, and the old, hardened grease will still be present albeit diluted by the oil component of the penetrating oil.

Grease and oil

Tribology is the science and art of reducing friction and wear of surfaces that rub or move against each other. Adequate lubrication is absolutely essential for the reliable function of almost any machinery, particularly for components that work under challenges like fast movement, heavy load, and high and varying temperatures. Such challenges are absent in microscopes, where oiling and greasing instead are expected to ensure precision and smoothness of the controls. Apparently, microscope manufacturers put a lot of effort in composing the perfect grease for every microscope function – some manufacturers are rumored to have used 10-20 different greases in every microscope. Their grease formulations were valuable trade secrets. Given all these efforts to perfect the lubrication it is today somewhat sad to realize how poorly many of these greases have aged. But on the other hand, perhaps it is unrealistic to expect that greases should be remain fully functional after 40+ years.

A universal requirement for microscope lubricants is that they must not contain any components that can evaporate and eventually condense as hazy films on the lens surfaces. Another concern is that silicone-based greases tend to creep along surfaces – therefore it may make sense to avoid these, or at least not to use them anywhere close to the microscope’s optics.

Finding the perfect grease for a particular microscope function is a daunting task. Not only that there are so many grease choices, but also because every mechanism design has its own requirements and idiosyncrasies. Some microscope functions have a broad tolerance for greases, other functions can be very uncompromising. The Leitz company earned its fame mainly for its mechanical and optical excellence, but also for the exquisite, smooth tactile feeling they managed to realize in their microscope and camera controls. Meticulously selected greases contributed a lot to their success.

Damping greases appear to be popular choices for microscope lubrication. A damping grease has a high shear resistance, which means that the sliding surfaces will stay put without backlash when the movement stops. As an example, for the focus mechanism it means that when you stop turning the coarse focus knob, the focus should remain exactly in the same position where it stopped without any sliding or drifting backwards. It’s a good idea to research suitable damping greases on the Internet. NyoGel (Nye Lubricants, part of the Fuchs Group) greases are often mentioned by amateur microscopists. Newgate Simms sells a damping grease trial pack comprising six damping greases (Tribosyn 320) with different viscosities. The trial pack can be useful to identify the best damping grease to pair with a particular microscope control. For other alternative microscope greases there are many recommendations on the Internet.

Aging of grease happens gradually and is therefore typically only recognized late when the grease already has become seriously degraded. After several years greases tend to lose their lubricating efficacy, they thicken, and may eventually solidify completely. It seems that contact with air and inactivity (i.e., no movement of the parts) are the main factors behind grease aging. Aged grease on brass surfaces acquires a characteristic green discoloration (due to chemical reactions with copper.)

Cleaning and removal of old grease, and application of new grease are essential microscope maintenance tasks that ideally should be performed regularly. Microscope components that are left with aging grease will become sluggish and may eventually seize or even break as the old greases lose their lubricating ability and harden. Dust and grime trapped by the grease only aggravate the problems.

Before applying new grease, it is important to thoroughly remove any old grease. There are some horror stories on the Internet where new greases have been applied over old grease and then within a short time the parts have seriously seized. Old grease is removed by wiping it off and cleaning with pieces of cloth or cotton swabs wetted with solvent (e.g., white spirit.) In difficult cases it may be necessary to soak the items in solvent for hours or days, or even to mechanically scrape off the hardened grease.

Sometimes a dark tarnish remains on metal surfaces, particularly on brass, even after cleaning with strong solvents. The tarnish doesn’t impair function per se, but it may possibly accelerate the decomposition of any freshly applied grease. The tarnish can be removed by rubbing with pieces of cloth or cotton swabs wetted with a suitable metal polishing agent (Autosol, Brasso, Peek, etc.) or, in more severe cases, by careful polishing with “super fine” sandpaper. After finished polishing, the remaining abrasive particles must be thoroughly removed by washing and brushing the parts with solvent (isopropanol) and then warm water with dish detergent.

Workflow

During microscope disassembly it is highly recommended to take careful notes and/or photographs to document every step and to be able to recall how all parts were assembled. It is also a good idea to compartmentalize the work by collecting the parts in separate boxes or containers that logically represent each functional unit.

Most of the maintenance notes describe a complete disassembly of the covered microscope component. Consider however that such a complete disassembly may be unnecessary; you may be able to limit the disassembly to only those particular parts that are needed to access and fix your specific problem. The key is to identify the problem and thoroughly think through the work required before getting started. Like they used to say, “measure twice, and cut once”.

Maintenance notes for microscopes from the Leitz "black era" (170 mm tube length)

Maintenance notes for microscopes from the Leitz "gray era" (170 mm tube length)

Maintenance notes for microscopes from the Leitz "white era" (160 mm tube length)