Question

Equipment used to work out the field of view for a microscope

Answer 1

They can use microscope with anything in tiny cells, bacteria etc

Answer 2

An ocular micrometer is basically a tiny ruler etched into one of the ocular lenses; it can give you a better estimate of the size of a cell, provided you calibrate it with a stage micrometer, which is a microscope slide that has a scale etched into its surface.