Microscopes

Microscopes are used to produce a magnified image of an object or specimen. There are two main types of microscopes:

-Compound light microscopes (resolution: 200 nm.) Light passes through a specimen, then through two sets of glass lenses called the objective and the ocular. Both bend the light to give a magnified image. It can be protenced into the eye or onto a photographic film (Photomicrograph). They are used to examine living and unstained organisms.
-Electron microscopes (resolution: 0,5 nm.) They use a beam of electrons instead of a beam of light. These have smaller wavelenght, so then more resolution. There are two main types:

1) Transmission electron microscopes (TEM): used for the ultrastructure of cells. The specimen should be thin. As the beam passes through the specimen, electrons are absorbed by heavily stained parts, but pass readily through lightly stained parts. Electromagnets bend the bends to focus an image in a fluorescent screen. Electron micrographs have a magnification of x250 000.

2) Scanning electron microscopes (SEM): 3D images of surface of specimens. It examines images of whole specimens (cells, tissues, organisms).

1 mm. = 10^-3 m. = 1/1000 m.
1 µm. = 10^-6 m. = 1/1000000 m.
1 nm. = 10^-9 m. = 1/1000000000 m.
1 m. = 10^3 mm. = 10^6 µm = 10^9 nm.