Requirements:
(1) microscope with a set of objective lenses, such as 10x, 25x, 40x and 100x.
(2) an etched micrometer scale placed in the microscope ocular lens
(3) a stage micrometer scale etched in 0.01 mm divisions, typically 0.3 mm in total length
For each objective lens, the number of units in the ocular micrometer needed to measure 0.1 mm is counted. Since 0.1 mm = 100 microns:
number of microns per unit at a given magnification =
= 100 / (number of units counted)
As the magnification power of the objective lenses increase, so do the number of ocular micrometer units it takes to cover the 0.1 mm.
For each microscope there will be a constant, so that:
constant =
= (number of microns per ocular micrometer unit) * (power of objective lens)
Once the constant is determined, then an estimate of the number of microns for each ocular micrometer unit for each objective lens can be made. This should be verified by actual calculation as outlined above.
