EXERCISE NO. 2 THE OCULAR MICROMETER Flashcards
The identification of parasites depends on several factors, one of which is size. The [?] are measured and are generally within a specific range.
length and width
There are different ways by which size can be assessed. The size can be estimated in relation to the microscope field which can be determined for each set of (?) and (?). This is called the (?). However, this technique is limited to larger object images. It would be a little difficult to compare very small object image in relation to the view field.
eyepiece field number and objective magnification
actual field of view
Jjk
Another method of measuring is to compare the (?) with one of another object or parasite species common in the locality whose size under the microscope is known (e.g. red blood cells, or eggs of Ascaris)
parasite size
Any laboratory doing diagnostic work in parasitology should have a (?) available for precise measurements.
calibrated microscope
Measurements of objects microscopically are made with an (?) (also known as the reticule). The ocular micrometer is a disc made of glass that is inserted into the eyepiece of the microscope
ocular micrometer
The (?) is etched with a measuring scale which is evenly divided into 50 or 100 units
micrometer disc
the (?) on the ocular micrometer represents different measurements as it changes with total magnification, and thus has no absolute value.
scale
does not have units and it needs to be calibrated prior to use
ocular micrometer
looks like a glass slide but has a scale of known true length etched on the surface
stage micrometer
typical stage micrometer scale is (?) long and etched with divisions of (?)
- 0 mm
0. 01 mm
It is just like a ruler and used to calibrate the ocular micrometer
stage micrometer scale
With the ocular micrometer set correctly inside the eyepiece, the stage micrometer is focused with an (?) (usually starting with the lowest power) of the microscope, making sure to make the scale as sharp as possible.
objective
can be rotated and the stage micrometer is moved on the microscope stage so that the two scales are parallel to each other
eyepiece
identified by the numbered divisions
ocular micrometer scale
does not show numbers but true lenght of each division is known (0.01 mm)
stage micrometer scale
simply superimpose the (?) onto the stage micrometer and note the relationship of the length of the ocular to the stage micrometer
ocular micrometer
When making measurements, it’s particularly important that the right (?) of measurements are used.
units
Measurements of parasites observed under the microscope are usually reported in
microns, µ
or micrometers, µm
One mm is equal to
1000 (µm)
The figures obtained from the calculations should be converted to (?) during measurements
micrometers
Each (?) of the microscope must be calibrated separately.
objective
is different at each magnification
calibration factor
The calibrated ocular micrometer can be used to measure any (?) in a microscope field since the ocular can be turned in any direction to align with the length or width of the object.
planar dimension
To measure the length or width of an object note the number of (?) spanned by the object. Then multiply by the calibration factor for the magnification used
ocular divisions
•After each (?) has been calibrated, the oculars containing the disc and/or
these objectives cannot be interchanged with corresponding objectives or oculars on another microscope.
objective
•Each microscope used to measure organisms must be calibrated as a (?). The
original oculars and objectives that were used to calibrate the microscope must also be used when an organism is measured.
unit
•The (?) containing the ocular micrometer can be stored until needed. This
single ocular can be inserted when measurements are taken. However, this particular ocular containing the ocular micrometer disc must also have been used as the ocular during microscope calibration.
eyepiece
•Post the (?) for each objective either on the base of the microscope or on a nearby wall or bulletin board for easy reference.
calibration factor
•(?) is usually repeated annually.
Calibration
•When the high dry and oil immersion objectives are used, the 0 line of the stage micrometer will (?), whereas the ocular 0 line will (?). The thin ocular 0 line should be lined up in the center or at one edge of the broad stage micrometer 0 line. Thus, when the second set of superimposed lines is found, the thin ocular line should be lined up in the center or at the corresponding edge of the broad stage micrometer line
increase in size
remain the same size
Ability to measure accurately the size of parasitic forms is often necessary in making species identification. This measurement can be made with a calibrated scale called
micrometer
are flat glass discs etched with a fixed scale, usually consisting of 50 or 100 small divisions. These divisions will have different measurement values depending on the power of the microscope objective used
Ocular micrometers
The measurement values are calculated using a (?) etched with a known calibrated scale of 0.1 mm divisions subdivided into 0.01 mm divisions
stage micrometer
- Remove the (?) (lOx or other) from the microscope and unscrew the top or
bottom lens, depending on its construction. Place the (?) on the diaphragm within the eyepiece with the etched surface on the undersurface of the reticule. Screw back the (?) and re-insert the eyepiece into the microscope
eyepiece
ocular scale
lens
- Place the (?) on the microscope stage and focus the low-power objective on some portion of the scale with the lOx eyepiece.
stage micrometer
- Adjust the stage micrometer by moving the stage so that the 0 line of the (?) is exactly superimposed on the 0 line of the stage micrometer
ocular micrometer
- Without moving the stage micrometer, find another point at the (?) where two other lines are exactly superimposed. This second set of superimposed lines should as far to the right as possible from the 0 lines. This distance will vary with the (?) used. At higher magnifications, the thickness of the (?) may be great that you need to look for superimposition of either the left or right edge of the individual lines
extreme right
objective
etched lines
- Count the number of (?) on the ocular micrometer between the 0 line and the point where the second set of lines is superimposed. In the example provided in the figure, this number, indicated by the dotted line, equals 33 ocular units
division lines
- Then count the number of (?) division lines between the 0 line and the second superimposed line on the stage micrometer; in the figure, this number, indicated by the arrowhead, equals 0.22 mm
0.1 mm
- Calculate the length represented by
one ocular unit
- When all the objective have been calibrated, prepare a simple chart that displays the (?) for each one
calibration factor
- With the ocular micrometer in place after calibration, focus on the object to be
measured and determine the size in
ocular units
- Calculate the size of the object by multiplying the (?) by the (?) for that specific microscope, objective and ocular micrometer
ocular units by the calibration factor
The (?) are arbitrary and a calibration procedure must be done to determine the calibration factor for each different objective and each different microscope
units of the micrometer disc
