A typical flatfield looks like the instrument shown below. This type of scope utilizes two separate optical paths. This is to say that there is a separate microscope for each eye. These are inclined at a six degree angle towards each other so that the user can see a portion of the sides of the specimen as well as the top. This separation of views allows us to perceive depth and see in true 3D, unlike with the flatfield.
Stereo microscopes come in many different forms.
Below is a common high quality stereo microscope. For the best and worst of this breed, please refer to our Stereo Microscopes to Buy and to Avoid publication.