A simple microprojector


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A simple microprojector
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Simmons, Samuel William
The Department. ( (Washington )
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aleph - 030609819
oclc - 79316393
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ET-104 May 1937

United States Department of Agriculture
Bureau of Entomology and Plant Quarantine


By S. W. Simmons, Division of Insects Affecting Mai, and Animals

Field workers at times find themselves in need of a method for reproduc-
ing images of small specimens mounted on slides when usual manufactured devices
for this purpose are not readily obtainable. In such instances a monocular
compound microscope can be made to serve as a microprojector by fitting it with
the simple mirror attachment described herein. This attachment can be made at
very little expense, and the necessary materials are usually available.

The apparatus consists essentially of a mirror so mounted near the
ocular of the microscope that the image is reflected downward on a piece of

The materials needed are as follows:

(1) One mirror of as nearly optically correct glass as possible,
approximately 1 by 1 inch. (Optically correct glass is needed.
otherwise the image will be distorted.)
(2) Metal frame for mirror.
(3) One metal bar about 3 inches long, 1/2 inch wide, and 1/16 inch
(4) One strip of spring steel or brass, approximately 3/4 inch
wide and about 21 inches long.
(5) Solder.

Figure 1 shows construction and assemblage of the apparatus. One end
of the metal bar is soldered to the back of a piece of thin sheet copper, brass,
or tin. This piece of metal should be about 1/4 inch greater on all sides
than the mirror. The mirror is then placed on the metal, face upward, on the
side opposite from the metal bar, and the edges of the metal are turned over
it to form a rigid frame.

To the opposite end of the bar and about 1 inches from the mirror a
spring clip is soldered as shown in the figure. This clips over the draw tube
of the microscope and holds the apparatus firmly in place. It is easily con-
structed from thin spring brass or steel.

The metal bar is bent so that it places the mirror directly in front of
the ocular lens, and at a 45 angle to it.


The apparatus is then clipped on to the draw tube of the microscope, and
the instrument is tilted back so that the draw tube is parallel with the table.
When a piece of white paper is placed beneath the mirror and the object on the
slide is brought into focus the image is reflected on the paper,

The mirror is properly adjusted when the field of light reflected is
circular. This can be determined by the use of a compass. Corrections are
made by bending the metal bar and turning the apparatus.

It is essential that the source of light be adequate and that the room
be darkened. Most medium-priced microscope lamps are probably satisfactory.
A small spot light on a universal-jointed mount is convenient, but such lamps
are generally not bright enough to use with high-power magnifications. The
brighter lamps with large lenses can be used successfully. Scattered light
from the lamp must be at a minimum, This can be reduced by placing the large
end of a metal funnel over the lens and directing the small end of the funnel on
the object. The condenser and mirror of the microscope can be removed or pushed
to one side and the light placed close beneath the specimen, care being taken
to avoid overheating. Colored glass filters are better removed from the lamp
before use,

The magnification varies with the distance of the mirror from the eye
lens, with the length of the draw tube, with the distance of the paper from
the mirror, and with the ocular and objectives used.

When the center of the mirror is 15 mm from the ocular and the paper is
51- inches below the mirror, as it is when lying on a table beneath the ocular
of the average microscope tilted parallel to the table, a magnification of
about 52.5 times can be obtained with a 16-mm objective and a lOx ocular. By
pulling out the draw tube the magnification is increased. Extending it 26 mm
increases the magnification to 64 times. With large lice, mites, etc.. a 32-mm
objective is convenient and does not require an especially strong light. A
very good light must be used with an objective less than 4 mm.

Specimens reflected in this manner can be traced conveniently. A small
mirror as recommended does not interfere with free use of the pencil when

Figure l.-Mirror attachment for microprojection,
assembled for use on a compound microscope.
Actual size.

3 1262 08721 6718
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