Micrometer, ocular stage

An ocular micrometer is a disk on which is etched a scale in units from 0 to 50 or 100. To determine the micrometer value of each unit in a particular eyepiece and at a specific magnification, the unit must be calibrated with a stage micrometer. A stage micrometer has a scale 2 mm long ruled in fine intervals of 0.01 mm (10 finl). 

Find a point far down the scales at which a line of the stage micrometer coincides with a line of the ocular micrometer. Count the number of ocular units and the number of stage units from zero to these coinciding lines. 

Before carrying out particle sizing on a sample, the microscope s ocular scale must be calibrated. This is normally done with a stage micrometer, which has a linear graduated scale. The micrometer is aligned with the eyepiece ocular to determine the length per ocular scale division. The ocular can then be used to read the diameters of particles on a slide. When sufficient particles are sized, the length-number mean can be calculated ... 

The value of each division of the ocular micrometer scale must be ascertained for each optical combination (ocular, objective, and tube length) by the aid of a stage micrometer. 

Insert the ocular micrometer within the tube of the ocular by placing it on the diaphragm of the ocular, and adjust the stage micrometer by placing it on the stage of the microscope. 

Focus the scale of the stage micrometer accurately so that the lines of the two micrometers will appear in the same plane. Make the lines on the two micrometers parallel each other. This can often be done by turning the ocular to the right or left while looking into the microscope. 

Make two of the lines on the ocular micrometer coincide with two on the stage micrometer. Note the number of included divisions. 

Multiply the number of included divisions of the stage micrometer scale by the value in microns given for each division and divide the result by the number of included divisions of the ocular micrometer scale. The quotient represents the value of each division of the ocular micrometer scale. 

To standardize the microscope, place the stage micrometer on the stage of the microscope, and by selection of oculars or by adjustment of the draw tube, or both, bring the diameter of the whole microscopic field to. 206 mm. When so adjusted, each field of the microscope covers an area of approximately 1/30000 cm. (actually 1/3028 cm.) This means that the dried milk solids from 1/300,000 part of a c.c of milk are visible in each field of the microscope. Therefore if the bacteria in one field only are counted, the number found should be multiplied by 300,000 to give the estimated number of bacteria per cubic centimeter. In practice, however, more than a single field is examined so that the number used for multiplication is smaller than this. 

Excision of precise pieces of the neural fold or neural plate in the chick host Very thin microscalpels (made up from insect pins or steel needles sharpened on an oil stone) are used to excise precise fragments of the folds and neural plate in 0- to 5-somite stage chick embryos in ovo. An ocular micrometer is used to measure the pieces of tissue to be removed. 

A hairline eyepiece, an ocular micrometer or standard graticule, and a stage micrometer, provided for microscopy. Routine laboratory material and ancillary instruments to carry out gravimetric testing, that is, balance, oven, desiccator, measuring cylinders, stop watch, watch glasses, and so on. 

At times, wine microbiologists may need to determine the size of the microorganisms being viewed to help to determine the identity of the microorganism in question. To do this, a separate ocular micrometer is placed into the eyepiece of a microscope but must be calibrated for each objective. Both ocular and stage micrometers are required. 

Place the ocular micrometer into the eyepiece and the stage micrometer onto the center of the stage. Viewed together through the eyepiece of the microscope, the micrometers appear as shown in Fig. 12.3. 

Figure 12.3. Views of ocular (A), stage (B), and both ocular and stage (C) micrometers used in microscopy. The lines on the stage micrometer are exacdy lOpm apart.

Count the number of ocular micrometer lines that exacdy occupy the space between two (2) stage micrometer lines. With four ocular lines per space on the stage micrometer lines, one space of ocular micrometer would be 10pm 4 = 2.5 pm. 

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