Microscopy
Introduction to Microscopy
- Microscopes are instruments which magnify tiny details so they can be seen clearly.
- The study of objects under a microscope is called microscopy.
- A typical school microscope is a light microscope, using light to magnify the objects up to 2000 times their original size.
- The metric scale used in microscopy is the micrometre (µm) or nanometre (nm).
Types of Microscopes
- The light microscope, as used in school laboratories, is suitable for viewing cells and tissues.
- The electron microscope uses a beam of electrons instead of light to magnify objects up to two million times, allowing viruses and molecules to be seen.
Parts of a Microscope
- The eyepiece lens (or ocular lens) is where you look through, usually with a magnification of x10 or x15.
- The objective lenses sit above the specimen, with typically three or four with different magnifications (e.g., x4, x10, x40).
- The stage is where the slide with the specimen is placed.
- The focus knobs adjust the sharpness of the image, with coarse and fine focus adjustments.
- The light or mirror helps illuminate the specimen for better visibility.
Preparing a Slide
- To view a specimen under a microscope, it should be thinly sliced and mounted on a microscope slide.
- A staining agent such as iodine or methylene blue could be used to increase contrast and highlight different components of the cell.
- A cover slip should be gently eased down to avoid trapping air bubbles which can obstruct the view.
Understanding Magnification and Resolution
- Magnification is how much larger the image is compared to the actual size of the object, while resolution is the detail that can be seen.
- The formula to calculate magnification is Image size = Actual size x Magnification
Health and Safety Considerations
- Always carry a microscope with two hands - one under the base and one on the arm.
- Ensure slides are disposed of correctly to prevent injury.
- Glass slides can break easily and cause cuts, so handle them with care.
Understanding the Limits of Microscopy
- Although microscopes enable us to see small structures, they have their limitations.
- Light microscopes are limited by resolution; two objects closer than 200 nm appear as one.
- Electron microscopes may provide clear images of extremely small structures, but they can't be used to view living specimens.