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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 |
| Focus knob ratchet tools |
|
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. |
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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.
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| A. |
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B. |
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Figure 2.
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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 |
Price/Each |
FB1222 |
Flinn
Microscope Maintenance
Kit |
$22.35 |
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| © 2006 Flinn Scientific,
Inc. All rights reserved. Reproduction
permission is granted to science
teachers who are current customers
of Flinn Scientific, Inc. No part
of this material may be reproduced
or transmitted in any form or
by any means, electronic or mechanical,
including, but not limited to
photocopy, recording, or any information
storage and retrieval system,
without permission in writing
from Flinn Scientific, Inc. |
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