(210) 590-9010 Fax (21
National Optical & Scientific Instruments Inc.
6508 Tri-County Parkway
Schertz, Texas 78154
Phone (210) 590-9010 Fax (210) 590-1104
156, 156-S, 157
Copyright © 1/2/01
National Optical & Scientific Instrument Inc.
Model 157 is illustrated below
Knurled diopter ring
Widefield 10x/18
Sliding interpupillary adjustment,
grips located on both left and right
side of diopter scale
Interpupillary scale
Mark on side of eyepiece tube
for indexing diopter reading
Viewing head of microscope
Head locking screw
Revolving nosepiece
Objective lenses
Arm of microscope stand
Rack stop adjustment screw
Specimen holder (mechanical stage)
Knurled locking screws for securing
specimen holder to stage
Abbe condenser 1.25 N.A.
Iris diaphragm lever
Swing-out filter holder
Tension adjustment collar
(behind focus knob on left side)
Coarse focus knob
Knobs controlling X and Y
movement of mechanical stage
Fine focus knob
Illuminator condenser
Power on/off switch and
fuse holder on back of base
Models 156 & 156-S Monocular Head
Thank you for your purchase of a National microscope. It is a well built, precision instrument carefully checked to
assure that it reaches you in good condition. It is designed for ease of operation and years of carefree use. The
information in this manual probably far exceeds what you will need to know in order to operate and maintain your
microscope. However, is provided to answer questions which might arise, and to help you avoid any maintenance
expense that may be unnecessary.
Your new compound microscope is a high performance microscope with high quality Achromatic objective lenses
that provide good resolution and optical centering. The microscope is designed with a built-in mechanical stage
providing a travel range of 70mm x 32mm in the X and Y direction with graduation reading up to 0.1mm for
accurate positioning of specimen. Also included is a ball bearing quadruple nosepiece, separate coarse and fine
focus, with slip clutch, to protect focus mechanism, spiral mounted N.A. 1.25 Abbe condenser and built-in 5 watt
fluorescent light source.
Carefully read these instructions before operating microscope. They will permit you to use your new microscope to
its fullest capability. Nomenclature used to describe components and controls is identified by referring to diagram
on page 2.
The microscope and accessories have been carefully packed to assure they reach you in the best possible
condition. Do not discard packing container or materials until all components are accounted for. Save packing
container in case microscope needs transporting to another location or shipped for repairs.
156 Monocular:
Stand with head, one eyepiece, one rubber eyeshield, three objectives, condenser,
specimen holder, blue filter, dust cover, 0.9mm “L” type key wrench (for eyepiece socket
set screw and tension adjustment collar) and 2mm “L” type key wrench (for rack stop
156-S Monocular: Stand with head, one eyepiece, one rubber eyeshield, four objectives, condenser,
specimen holder, blue filter, dust cover, 0.9mm “L” type key wrench (for eyepiece socket
set screw and tension adjustment collar) and 2mm “L” type key wrench (for rack stop
157 Binocular:
Stand with head, two eyepieces, two rubber eyeshields, four objectives, condenser,
specimen holder, blue filter, dust cover, 0.9mm “L” type key wrench (for tension adjustment
collar) and 2mm “L” type key wrench (for rack stop adjustment).
1. EYEPIECE (ocular lens): Lens closest to the eye, magnifies the primary image formed by the objective lens.
2. OBJECTIVE TURRET (nosepiece): Revolving turret which holds objective lenses, permits changes of
magnification by rotating different powered objective lenses into optical path. Reverse position permits easier
access to stage when positioning specimen slides.
3. OBJECTIVE LENS: Lens closest to the object being viewed, forms first magnified image of the specimen.
4. MECHANICAL STAGE: Permits precise, mechanical manipulation of the specimen slide.
5. STAGE: Platform of the microscope where the specimen slide is placed.
6. CONDENSER: A 1.25 N. A. Abbe condenser lens positioned under center of stage, condenses light rays from
substage illumination and fills the back lens element of objective lens to improve image resolution.
7. IRIS DIAPHRAGM: Attached to bottom of Abbe condenser, controls aperture of light by moving control lever
left or right.
8. SAFETY RACK STOP: When properly adjusted, controls maximum upward travel of stage. Prevents higher
power objectives from breaking specimen slides, prevents damage to objective lenses. This stop has been preadjusted at the factory.
9. FOCUSING KNOBS: Coarse focusing knobs (larger knobs) located on each side of arm, raise or lower stage to
bring specimen image into focus. Fine focus knobs (smaller knobs located just below coarse focusing knobs)
permit more precise image adjustment.
10. ILLUMINATION: Built-in substage electric illuminator provides constant, reliable pre-focused illumination.
Observe that the main voltage of your microscope is labeled on the back of the base. Make certain that
the main voltage of your microscope corresponds to the voltage of your power outlet, 120v or AC.
1. Illumination.
A. Insert microscope plug into outlet.
B. Push rocker switch at rear of base to ON position.
C. In case of equipment malfunction, see “Trouble Shooting” procedures.
2. For model 157 binocular head only, interpupillary adjustment of viewing head
A. Look through microscope and adjust distance between the two eyepiece tubes by grasping the sliding
mounts to left and right of eyepieces and sliding together or apart.
B. When a full field of view is observed through both tubes, and images blend into one, interpupillary distance
is corrected for your eyes. Check the interpupillary scale and note index reading for future reference, in
case other users will be changing this adjustment from time to time.
C. Adjust the diopter scales, located on each eyepiece tube, to the same numerical value as indicated on the
interpupillary scale. This must be done in order to maintain parfocality of objective lenses. If interpupillary
distance is changed, adjust eyepiece diopters accordingly.
3. Focusing the microscope.
A. Position the 4x objective lens into the optical path, making sure that lens is properly indexed in its click-stop
B. Swing moveable finger on slide holder outward. Place specimen slide (cover slip up) on top of stage
surface against fixed side of slide holder. Slowly release moveable finger until it makes contact with
specimen slide.
C. Rotate coarse focusing controls until specimen comes into focus.
D. Adjust fine focus controls until specimen is in sharp focus.
E. For model 157 binocular head only, adjust diopter for possible difference in eyesight between user’s left and
right eyes. If user has 20/20 vision, this adjustment should not be necessary.
a) Using right eye, peer into the right eyepiece tube. Adjust sharpness of image by utilizing fine focus
controls, without touching the diopter ring.
b) Using left eye, peer into the left eyepiece tube. Adjust sharpness of image by turning diopter
adjustment located on left eyepiece tube.
F. Adjusting the aperture (opening) of iris diaphragm.
Iris diaphragm should not be used to control the brightness of illumination. Iris diaphragms are designed to
help achieve high resolution of specimen and provide contrast in the image. Smaller apertures will deliver
higher contrast to image. However, closing aperture too much will reduce resolution. Experimentation is
the best method of determining the correct opening of diaphragm. Some suggested openings for iris
diaphragm are:
From fully closed to 1/8 open
1/8 to 1/4 open
1/4 to 1/2 open
1/2 to 3/4 open
G. Usage of blue filter (one 32mm O.D. transparent blue filter has been provided with your microscope)
a) Placing a filter into the optical path will absorb some of the light from the illuminator base, limiting the
light output. Filters should only be used when they help enhance the image.
b) The fluorescent bulb in your microscope produces daylight type of illumination. Use of the transparent
blue filter will produce a slightly blue light, and blue filter does not need to be used with this microscope
under normal circumstances.
c) To insert filter, grasp filter holder knob and swing out filter holder, insert filter into slot provided and
swing filter into optical path.
d) When handling the filter do not touch lens surfaces as fingerprints and smudges will result in poor
H. Changing magnification.
a) Rotate revolving nosepiece to position 10x objective into optical path.
b) This microscope has been parfocalized, which allows changes from one objective to another while
requiring only a slight adjustment of the fine focus controls.
c) When changing to the 40x and 100x objective lens, care must be exercised when positioning these
lenses into the optical path, in order to prevent damaging the front lens element and specimen slide.
d) In order to obtain maximum resolution of the 100x oil immersion lens, it is necessary to apply
immersion oil between the coverglass of slide and front lens of the objective.
(1) Use of a very small amount of immersion oil is required.
(2) All air bubbles must be removed from between lens and slide by gently rotating nosepiece back and
Objective Specification Chart
Din 4X
Din 10X
Din 40X
Din 100X
Color Code
Field of
Models 156-S and 157 only
Magnification with
WF10X eyepiece
When finished viewing, all parts that come in contact with oil must be cleaned. Failure to do so could
permanently damage the 100x oil immersion objective lens. Use Windex to clean immersion oil off lens
surfaces is recommended.
WARNING: For your own safety, turn switch off and remove plug from power source before maintaining
your microscope. If the power cord is worn, cut or damaged in any way, have it replaced immediately to
avoid shock or fire hazard.
A. Do not attempt to disassemble any lens components. Consult a microscope service technician when any
repairs not covered by instructions are needed.
B. Prior to cleaning any lens surface, brush dust or lint off lens surface using a camel hair brush. You can also
use an ear syringe or canned compressed air, such as that sold by most computer stores.
C. Do not remove eyepieces or objective lenses to clean. Clean only the outer lens surface. Breath on lens to
dampen surface, then wipe with lens paper or tissue or use a cotton swab moistened with distilled water.
Wipe lenses with a circular motion, applying as little pressure as possible. Avoid wiping dry lens surface as
lenses are scratched easily. If excessive dirt or grease gets on lens surfaces, a small amount of Windex
can be used on a cotton swab or lens tissue. To clean objective lenses, do not remove objectives from
microscope. Clean front lens element only, following same procedure.
NOTE: Fingerprints or other matter on the front lens element of the objective lens is the single most common
reason that you will have difficulty in focusing the microscope. Before having costly servicing done, or
before returning to National for “warranty repair”, make certain to examine the front lens element with a
magnifying glass or eye loupe for the presence of such contaminants. If a microscope is returned to
National for warranty repair, and it is determined that such contaminants are the problem, this is not
covered under warranty and National will submit a cost estimate for cleaning.
A. The rack stop screw has been pre-adjusted at the factory and should not require re-adjustment. However, if
you do attempt re-adjustment, note the following procedure.
Using a 2mm “L” type hex key wrench, loosen rack stop socket set screw. With fine focus adjustment at
mid-range, focus on standard slide until sharp image is obtained. Rotate rack stop set screw in clockwise
direction until tight.
B. Coarse focus tension adjustment prevents the stage from drifting down from its own weight and causing the
image to move out of focus. This has been adjusted at the factory, but over the course of time it may loosen
and cause the stage of the microscope to slip downward on the focusing block.
The tension adjustment collar is located between arm and coarse focus knob on right side of microscope.
Using a 0.9mm “L” type hex key wrench, loosen the set screw located in the hole on tension adjustment
collar. Turn collar clockwise to tighten tension, counter-clockwise to loosen tension. Use of a wide
rubberband will provide a better grip on the tension adjustment collar. After adjusting, tighten the set screw
to lock collar in place.
NOTE: It is recommended that you leave the tension as loose as possible for ease of focusing, yet not so
loose that it permits the stage of microscope to drift downward from its own weight and cause the
microscope to “drift” out of focus.
C. Metal parts: Use a clean, damp cloth to remove dust or dirt from metal parts, followed by a dry cloth.
A. The extent of electrical maintenance, by other than a qualified technician, should be bulb replacement. BE
B. To replace bulb (National #800-138) .... gently lay microscope on side. Using a Phillips (cross-head) type
screwdriver, remove 5 each 3mm Phillips (cross-head) screws from bottom of base. Remove base plate to
expose bulb. Bulb is held in place by spring pressure clips and is removed by gently pulling bulb straight out
from socket. Replace with new bulb. Replace base plate and 5 Phillips (cross-head) screws.
C. Replacement of fuse (National #801-160)
The fuse is located at rear right side of microscope base. To remove fuse from holder, insert a 6mm
screwdriver blade into slot located in rear of fuse holder cap. Slightly depress and rotate screwdriver ¼ turn
in direction of arrow, release pressure on screwdriver to release the fuse. Pull cap and fuse out of fuse
holder. Insert proper 0.5 amp time delay fuse into fuse cap. Insert fuse cap into fuse holder. Using
screwdriver, rotate fuse cap assembly in opposite direction of arrow until guide slot engages, depress fuse
cap and rotate ¼ turn to lock into fuse holder.
Light fails to operate.
Image does not remain in focus
Image will not focus
Poor resolution
(image not sharp)
Spots in field of view.
Outlet inoperative.
Have qualified service technician
repair outlet.
AC power cord not connected.
Plug into outlet.
Lamp burned out.
Replace lamp.
Fuse blown.
Replace fuse (0.5 amp time delay
5mm dia. X 20mm long)
Adjust tension control.
Stage of microscope drops from
its own weight.
Rack stop not set at proper
Adjust rack stop.
Slide upside down.
Place slide on stage with cover
slip up.
Slide cover slip too thick.
Objective lenses dirty.
Use 0.17mm thick cover slip
(No.1 cover slip)
Clean objective lenses.
Eyepiece lens dirty.
Eyepiece or condenser lens dirty.
Clean eyepiece lenses.
Clean lens. ***
Specimen slide dirty.
Clean slide.
***Spots in field of view can also result from dirt on inside of eyepiece. It is recommended that you have
service technician clean inside of lens.
WF10x eyepiece w/reticle, 10mm/100 div.
WF15x eyepiece w/pointer
Replacement bulb, 5 watt fluorescent
Replacement fuse, 0.5 amp, time delay for 110 volt.
Please see our website, www.nationaloptical.com, for complete warranty details and exclusions.
(Revised 2/16/12)
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