Light Microscope
A light microscope illuminates the specimen by focusing light through a lens onto the microscope slide. The light passes through the specimen and into the objective lenses. Typically, a light microscope contains several objective lenses for different magnifications. The objectives are fixed on a revolving nosepiece that sits above the sample on the stage, this nosepiece can be turned to move a different objective into the light path. Each objective is marked with a colored ring indicating the magnification. The size of the objective is also indicative of the magnification; the 5x objective is much shorter than the 100x objective. The total magnification of the image results from multiplying the objective magnification by the eyepiece magnification, which normally is 10x. Thus, if you observe a slide using the 5x objective, you are magnifying the sample 50 times.
Figure 1: Parts of the light microscope: 1. Eyepiece, 2. Interpupillary adjustment, 3. Binocular tubes, 4. Head, 5. Stand, 6. On/off switch, 7. Illumination intensity control, 8. x-y translation mechanism, 9. Tungsten halogen lamp, 10. Base, 11. Collector lens, 12. Field diaphragm, 13. Field lens, 14. Condenser, 15. Mechanical stage, 16. Specimen holder, 17. Objective, 18. Revolving nosepiece, 19. Beam splitter, 20. Objective lens.
To examine a specimen, the revolving nosepiece is turned to the lowest magnification before the microscope slide is placed onto the microscope stage, as it is much easier to focus on the specimen at low magnification. The objectives are designed to be