The upright microscope is perhaps the most commonly used and features that the objective is facing downwards.
Where and when an upright microscope is used?
The upright microscope, in the case of "biological" samples, is used for samples placed on a classic slide.
The sample is then placed on a slide, treated in the best way for the observation method to which it must be subjected and then covered with a coverslip with a thickness not exceeding 0.17 mm.
Due to its construction, the upright microscope can only work with slides.
It is not possible to work with other coverslip thicknesses: the image would not be in focus or not sufficiently clear.
Inverted microscope, instead, has an opposite construction to the upright microscope.
In this case the objective is facing upwards and the sample with the surface to be examined is placed on the microscope stage.
Where and when an inverted microscope is used?
The inverted microscope is mainly used in laboratories where cell cultures are treated.
In these laboratories plastic vessels are used (Petri, Terasaki, flasks or other containers) with bottom thicknesses greater than 0.17 mm.
Sometimes slides are also observed but in this case the specimen placement has to be opposite with respect to the upright: the glass slide thickness (1.2 mm) must be facing the objective.

---