Overview
This lecture covers the parts and functioning of a compound light microscope, including how to focus specimens and understand magnification.
Parts of a Compound Microscope
- The foot is the base that supports the entire microscope.
- The arm is an arched structure holding the body and connects the base to the lenses.
- The body holds two types of lenses: eyepiece and objective lenses.
- The eyepiece lens, located at the top, usually has magnification options like 10x, 15x, or 25x.
- The nose piece is a rotating disc at the base of the body that holds multiple objective lenses.
- Objective lenses have different magnifications, commonly 10x (low), 45x (medium), and 100x (high).
- The stage is a metallic platform where the specimen slide is placed and held by clips.
- The microscope uses an LED bulb or a mirror as its light source.
- The mirror is plano-concave, with one flat and one concave side for focusing light onto the specimen.
- The diaphragm, similar to the iris in the eye, adjusts the amount of light entering the stage.
Focusing Mechanism
- The coarse adjustment screw moves the body up and down for rough focusing by changing the distance between stage and lenses.
- The fine adjustment screw makes precise, small adjustments to focus the specimen without moving the body visibly.
Preparing and Observing Specimens
- Specimens are placed on glass slides and covered with thin coverslips to protect and preserve them.
- Slides are secured on the stage with clips; some microscopes have screws for moving slides precisely.
- Light passes through a stage aperture to illuminate the specimen.
- To get total magnification, multiply the eyepiece magnification by the objective lens magnification (e.g., 25x eyepiece and 100x objective gives 2500x).
- Proper focusing and adjusting the light source are necessary for clear observation.
Key Terms & Definitions
- Compound microscope — uses two sets of lenses for higher magnification.
- Light microscope — uses light to illuminate specimens.
- Eyepiece lens — top lens you look through, magnifies the image further.
- Objective lens — lens closest to the specimen, major magnification.
- Nose piece — rotatable part holding objective lenses.
- Stage — platform for holding specimen slides.
- Coarse adjustment screw — moves the body for rough focus.
- Fine adjustment screw — fine-tunes the focus.
- Diaphragm — controls the amount of light reaching the specimen.
- Coverslip — thin glass protecting the specimen on the slide.
Action Items / Next Steps
- Practice identifying microscope parts and their functions.
- Prepare a slide with a specimen and practice focusing using both adjustment screws.
- Review how to calculate total magnification.
- Optional: Visit the academy website for more resources.