Corrections

The results, not only of this experiment, but even the one of experiments like this, are very important because the correct use of microscope is based especially on a good knowledge of the components which compose it and their operation.

Furthermore focalization is the base procedure that allows the visualisation using the optical microscope, procedure that must be done in the right way in order to find out satisfactory results in every possible following scope in which the microscope is used.

Calculate the diameter of the vision is useful to know approximately the size of the element you're enlarging, this is a basic information if we are dealing with observation, and maybe even of following classification, of the observed material.

In our case, with a scale of 4x, the diameter of the vision is 4,5 mm.

You can reach this aims using only a optical microscope and a slide, or however some generic material which is not inside a slide, placed in a thin layer and arranged in the mechanical stage in the right position.