Measurement by Eyepiece Graticule

Microscopy Methods in Microbiology
Microscopy Methods in Microbiology Part 1
Measurements with Optical Microscope
Linear Measurements
Measurement by Eyepiece Graticule
Measurements by Filar Micrometer
Measurements from Photomicrographs
Measurement of Volume or Thickness
Measurements of Area
Electron Microscopic Method for Micrometry
Observation of Microbes in Living State - Introduction
Wet Mount or Wet Film Preparations
Observation of Bacteria Protozoa and Algae
Observation of Fungi
Hanging Drop Preparation and its Modifications

Measurement by Eyepiece Graticule

	Measurement by eyepiece graticule: This is a device in which the dimensions of the object are measured with the aid of (i) special ocular containing graduated scale called ocular micrometer and (ii) stage micrometer. The stage micrometer is a glass slide (3" x I”) on which a millimeter (mm) scale is imprinted. Graduation of this scale is in hundredths of a millimeter. The measurements of a microscopic object by this mode require, first the standardization or calibration of ocular micrometer with the stage device. This is done by replacing the normal eyepiece of the microscope with the ocular micrometer. On replacing and looking through, the ruled lines of ocular micrometer.
The ruled lines of stage micrometer whenlooked through normal ocular. Using objective that is to be used for the measurement of the specimen and ocular micrometer, bring the stage micrometer in focus, so that the long axis of the two scales are aligned in parallel and the vertical rules of calibration lie over each other with both scales precisely in focus, move the stage so that one of the graduations of stage micrometer exactly coincides with the graduation of the ocular micrometer. Examine the scale. Note where the above situation is repeated and calculate how many divisions of ocular micrometer are equivalent to how many on the stage micrometer. Derive the value in terms of microns of one smallest scale union the ocular micrometer.
The value of each division of ocular micrometer depends on the length of microscope body tube and the objective used. For example, 100 eyepiece divisions correspond to 10 stage divisions. The distance of 10 stage divisions is known (0.1 mm). Therefore, the value of single ocularmeter unit (O) for the given optical conditions may be represented as, O= = =10x10-3 mm (1μm)
On completion of ocular micrometer calibration, remove .the stage micrometer and place the specimen to be measured. Focus the specimen and count the number' of divisions (N) covered by the specimen (Figure 2-13d). The size of the specimen can be calculated by multiplying the number of divisions (N) covered by the specimen with value of unit division (O).

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