What is the approximate size of the smallest object visible with a brightfield light microscope?

Question

What is the approximate size of the smallest object visible with a brightfield light microscope?

Answer 1

The best resolution achieved with a brightfield microscope is 0.2 micrometers.  What this means is that if two objects are closer than 0.2 micrometers, they will merge into one and you won't be able to tell that they're distinct objects.  Some different techniques in light microscopy can increase the resolution to 0.1 micrometers.  

Answer 2

The light microscope renders objects as small as 0.2 microns (1 micron = 10-3mm) visible to our eye.