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Teacher Resources

Microscope Maintenance Tips

Introduction:

The procedures outlined below are designed to assist in routine optical and mechanical maintenance of simple compound microscopes. These suggestions are not intended to replace directions in manuals for specific microscope models. Periodic service of your microscopes is recommended. This should be done only by qualified technicians since general servicing includes disassembly and inspection for wear, as well as cleaning and lubrication. How frequently your microscopes are serviced is somewhat dependent upon the hours of use. As a general guideline, compound microscopes should be serviced after about 200 hours of continuous use. This will translate to about every three years for most schools. If the microscopes are used for multiple courses or continuously every day, the frequency of service will increase. The routine procedures outlined below can help reduce the frequency of major microscope repairs.

Materials Needed (Included in Flinn Microscope Maintenance Kit FB1222):

Aspirator/brush                      Lithium grease
Q-Tips®                      Set screw adjustment tools
Lens cleaning solution                      Lens paper
Magnifier                     


Getting Started:

To clean or adjust a microscope, pick a large, flat working area where your tools, manuals and any parts you remove can be laid out in a systematic and clean fashion. Clear the area of all unnecessary items and have some clean paper towels or cloths available. Petri dishes are ideal for holding small parts and preventing them from rolling off your work surface. Clean the work area to remove all dust and dirt and avoid drafty areas with any particulate or chemical pollutants.

Most simple compound microscopes work on the same principles but vary greatly in their mechanical design and their various operating parts. Before starting, locate and carefully study the manual for each model of microscope on which you are going to work. Note any unique tools that may be required for the specific microscope such as tension wrenches, jeweler's screwdrivers, allen wrenches, etc. Be sure all necessary tools are on hand before starting work. Some microscopes have complex mechanical systems with shims and bearings and should probably be serviced for mechanical adjustments by trained technicians. In fact, after studying the manuals, if you are not comfortable, you may want to confine your maintenance efforts to "optical" maintenance and leave all mechanical adjustments to the experts.

Basic Handling/Storage:

The most critical step in microscope maintenance is prevention. Instruction about the proper carrying, handling, use, and storage of the microscope is the greatest single thing that can be done to avoid major microscope repairs.

Keep microscopes covered when not in use. Microscope life is extended when they are stored covered. This should be done even if they are stored in a cabinet. Plastic bags should be used if microscope covers are not available. Never store a microscope with the eyepiece removed or uncovered, since dust will collect in the body tube and be very difficult to clean. Keep the body tube sealed at all times.

When finished using a microscope with an electric illuminator, turn the illuminator off and let it cool for several minutes before moving the scope to put it away. This cooling off period will extend the life of the bulb.

If oil immersion is used, the high power objective lens and the lens of the condenser should be thoroughly cleaned before microscope storage. Never store microscopes in chemical storage areas where corrosive fumes might etch lenses or destroy metal parts.

Optical Maintenance:

Lens Cleaning:

All lenses are made of coated, soft glass and can be easily scratched. Lenses should be treated with care. Never use a hard instrument (such as a dissecting needle, etc.) or abrasive to clean a lens.

For the top of the eyepiece and the ends of the objectives, clean as follows: Use a camel's hair brush and an aspirator to remove all loose dust and dirt. Then moisten the end of a Q-tip with lens cleaning solution. Keep the other end of the Q-tip dry. Clean the optical surface with the moist end of the Q-tip using a circular motion. Dry the surface with the dry end of the Q-tip using a circular motion. Use an aspirator or similar air source to remove any lingering dirt particles.

Immersion oil should always be wiped from all surfaces immediately after use. In the event immersion oil is allowed to harden, moisten a piece of lens paper with a small amount of xylene and use this to redissolve and remove the hardened oil. Note: Xylene may leave a film on the lens and may dissolve the cement used to seal the immersion objective. To prevent this, always moisten a second lens paper with alcohol and use it to remove any residual xylene. Repeated use of xylene will destroy lens coatings.

To determine which lens surfaces need cleaning, focus the microscope on a clean slide free of all dust. Moving the slide will determine if the visible dust is on the slide. Rotating the eyepiece will establish if dirt is on the eyepiece. After loosening the retaining screw (if there is one) rotate the eyepiece in a circular fashion. If any dirt rotates, the eyepiece needs cleaning. Remove the eyepiece and clean it. Be careful not to damage any pointers. Clean the eyepiece on both ends in the same fashion described above for the objectives. When the eyepiece is thoroughly cleaned and dried, replace it and refocus the microscope.

Cleaning Objectives:

Moving other parts will likewise help determine where dirt exists. Dirt on mirrors can be detected by moving the mirror while looking through the microscope. Rotating objectives will establish if dirt is on a specific objective. Does the specific dirt move or stay when objectives are rotated? Dust on a condenser lens can be detected in a similar fashion. Substage condenser lenses and mirrors should be cleaned with lens paper.

If the lower exterior surface of an objective has been cleaned and dirt still persists, it may be necessary to clean the inside surfaces of the objective. To do this the objective lens should be carefully removed from its nosepiece mounting. The objective lenses are threaded into the nosepiece and must be carefully removed for cleaning. This should be done with the utmost care to avoid stripping the threads and/or scratching the finish on the objective. Apply a firm, even pressure on the serrated top of the objective while holding the nosepiece from turning. A padded wrench or leather strip may prevent scratching of the objectives. Do not overtwist. If the objectives seem too difficult to loosen with a small wrench, call a microscope repair technician.

Clean the inside of the objective lens just like the outside, try to avoid lint and dust from getting back inside the objective. An aspirator is very helpful when working on the inside of an objective lens.

If after cleaning all surfaces carefully, dirt is still found in the field of view, it is possible that dirt is between the lenses of the objective. This dirt cannot be removed without disassembling the compound lens in the objective. Do not attempt this-call your microscope repair technician.

Mechanical Maintenance:

Most microscopes require periodic cleaning, lubricating and minor adjustment of their mechanical parts. The normal adjustments that are required for your particular model of microscope are probably outlined in its maintenance manual. General guidelines are provided here.
Caution: Never overtighten or use force when doing any repair/maintenance of your microscope.All high quality microscopes are manufactured from brass or other soft metals and are easily damaged with excessive force.

Mechanical adjustments of most microscopes are of several types. Each model of microscope, however, may have different methods of adjustment. Mechanical parts of some microscopes are exposed and openly visible, while others are concealed and require the removal of plates for repair procedures.

Microscopes with inclination joints often become too loose or too tight. Usually a round nose pliers, used as a wrench, can be used to adjust the tension by turning the adjustment collar on the outside of the inclination joint.
micromaint1.gif
Figure 1. Basic microscope with illuminator.



Nosepiece Adjustment:

The nosepiece can likewise become too loose or too tight. There is usually an adjustment mechanism on the nosepiece. It is often as simple as loosening or tightening the slot-headed screw in the middle of the nosepiece. Sometimes there is a two-hole ring nut. This requires using a round nose pliers like a wrench to loosen or tighten the collar. On some microscopes the stage must be removed to gain access to the nosepiece adjustment. Be sure to check the manual for your specific microscope.

Focus Knob Adjustment:

Tension of the coarse and fine adjustment knobs can be adjusted. Again, various mechanical methods have been designed. Some microscopes are adjusted by simply turning the knobs on each side of the microscope in opposite directions to tighten or loosen as desired. Others have adjustable collars on the shaft and require the use of specially designed collar-wrenches or allen wrenches to make the adjustments. Moving the collars out usually provides more tension. If your microscope requires unique collar-wrenches, obtain these from your microscope supplier.

Moving Surfaces:

Sliding surfaces on the microscope can be cleaned and lubricated. This should be done on an annual basis. It is a good idea, on a weekly basis, to put the microscope through its paces. During normal use, the mechanism is probably not worked through its full range of motion. Lubricating grease can build up and harden because it does not remain evenly distributed. To remedy this, rotate both coarse and fine focus knobs from end-stop to end-stop several times. Be sure to rotate the low power objective into place before performing this procedure.

micromaint2.gif            micromaint3.gif
A.            B.

Figure 2.  Some coarse adjustment knobs can be rotated in opposite directions to adjust tension (A), while other microscopes require tension wrenches to rotate collars for tension adjustment (B).



Clean any grease and dirt from all sliding surfaces, using clean paper towels and a solvent such as alcohol. Wipe completely dry. Apply a thin layer of fresh grease to the sliding surfaces. Lithium-based grease or other grease specified by the manufacturer is recommended. Do not oil or grease the teeth of the rack and pinion gears.

If any parts or plates were removed, be sure to replace them in reverse order of their removal. Do not force any parts back together. After lubrication, the coarse adjustment may move too freely. If it does, adjust the coarse adjustment knob tension as described earlier.

Bulb Replacement:

Instruction for replacing the bulb in each specific microscope is found in its corresponding user's manual. Always allow a bulb to cool before attempting to replace it. The incandescent bulbs found in most traditional microscopes will usually last for approximately 100 hours. Fluorescent-type bulbs will last significantly longer. All incandescent bulbs are susceptible to broken filaments by excessive jarring and, therefore, replacements should be available. When replacing bulbs, avoid touching the glass with your bare hands. Fingerprints left on the bulb will actually "burn into" the glass and reduce the bulb quality and life expectancy.

Term Definition
Condenser A lens or system of lenses which collects light rays and converges them to a focus.
Depth of field The ability of a lens to furnish an image above and below the focal plane; depth of field decreases with the increase in aperture or with an increase in magnification.
DIN (Abbreviation for Deutsches Institut fur Normung) A German national standards body which has set internationally accepted standards for a variety of devices, including optics.
Field of view The area which is seen through a lens system. In a microscope, it is the circular area viewed through the eyepiece. It will vary depending upon the magnification.
High power The high power objective in the nosepiece of the microscope. Usually the objective in the 40X range is called the high power objective. If the scope has an oil immersion lens (100X), it is not referred to as the high power objective.
Intermediate power The middle power objective; usually 10X.
Low power The lowest power objective; usually 4X.
Magnification The number of times an object is increased in size by a lens system.
Numerical aperture (N.A.) A mathematical formula devised by Ernst Abbe for the direct comparison of the resolving power of objective lenses; the higher the N.A. the more complex and expensive the lens system becomes.
Parfocal Characteristic of a microscope which allows the rotation from one objective to another and only requiring a small, fine focus adjustment to be in focus.
Ocular lens The lenses closest to the eye; also called the eyepieces.
Objective lens Any of the compound lenses mounted on the nosepiece.
Oil immersion A high power objective (usually 100X) which requires an oil medium to focus the maximum light when in focus.
Rack and pinion A device for interconversion of a rotary motion and a linear motion. Turning the pinion (small cog wheel) engaged in the rack (toothed bar) causes the slow linear motion of the up and down movement in the microscope.
Resolving power The capacity of the optics to distinguish and separate fine detail, i.e., two points. The resolving power is limited by the N.A. of the objective and the substage condenser. The higher the N.A. the greater the resolving power.


Figure 3. Glossary of terms often used in repair manuals.

Flinn Microscope Maintenance Kit is available from Flinn Scientific, Inc.:
Catalog No.
Description

 

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