Micrometry: Definition and Types | Microbiology

Micrometry is the science in which we have some measurement of the dimensions of an object being observed under the microscope. The method employs some special types of measuring devices which are so oriented that these can well be attached to or put into the microscope and obser­ved. The object, to be measured, is calibrated against these scales.

Once we are observing an object under a microscope by the 5X objective and the 10X eye­piece we say that the image that we are able to perceive is 5 × 10 = 50 times of the object.

We get the magnified view no doubt and also that it is the perfect coordination of the dimensions, but to find out the exact size of the object will need precision and that is achieved through the application of some small scales called micrometers.

Types of Micrometry:

There are usually two types of micrometers, i.e. stage micrometer and ocular meter or ocular micrometer (Figs. 104, 105).

i. Stage Micrometer:

As is clear from its name it is for the measurement on the stage of the microscope where an object is to be kept. This micrometer is of a slide’s shape and size and has a mount of very finely graduated scale. The scale measures only 1 mm and has a least count of 0.01 mm, i.e. 1 mm region is divided into 100 divisions. As 1 mm has 1000µ, one division of stage micrometer is equivalent to 10µ.

ii. Ocular Meter:

This micrometer is used inside the eyepiece. The upper eye lens is unscrewed and the ocular meter is put into the tube of eyepiece, and the eye lens is again replaced in its original position. There are usually 50 or 100 divisions in the ocular meter which are engraved on the glass.