Microscope. An optical (light) microscope with a mirror for reflecting light. The (black) chamber running from upper centre to centre is the lens unit. This has the eyepiece at top (silver, containing the eyepiece lens). The three objective lenses (silver at centre) rotate on a wheel to give a choice of magnification. At lower centre is the specimen table with a mirror below to reflect light upwards, back to the specimen and eyepiece. Focus is adjusted using the circular silver knob (at upper right) which moves the lens unit up and down. Objects are magnified by the combination of eyepiece and objective lenses.