They also have heads that change angle to suit you. Take a look at industrial microscopes you bio folks, it will do you good. The key to reflected light is the word reflected. We are dealing with reflection as well as refraction. If the material doesn't reflect then there is no image.
Refraction is an image source from knife edged plateaus on the specimen.
An example of this is semi-conductor lines located above the silicon substrate. To get reflected light we must have a light source, a powerful one, and an illuminator. The light source should be a strong light source since many specimens in reflected light work are very dark, metals, coal, etc. The illuminator has a semi- silvered mirror that reflects the light from the light source down through the objective. The objective acts as both condenser and objective.