The observation tube has two places to put eyepieces, also called oculars. We aren't going to call them oculars because it is yet another confusing term. The eyepieces magnify the image and provide a place to put measuring reticule. Research microscopes usually have a place in the frame to put reticules. This allows the reticule to be photographed with the specimen.
Any module located between the limb and the binocular tube is called an intermediate piece.
These include fluorescence, reflected light, multi-veiw and magnification changers modules. When you are calculating the total magnification of the microscope you must include any intermediate pieces. The stage sits below the nosepiece and supports the specimen. Most modern stages are mechanical with low, coaxial controls. This means that there is a single control hanging down from the stage that moves the specimen.