Light microscope

A light microscope works like a refracting telescope except that the object is very close to the objective lens. An object to be studied, for example a tiny organism so small it looks like just a dot, is put on a slide, which is usually a flat piece of glass. The clips on the microscope's flat stage hold the slide in place. The stage can be adjusted to add more light. It also moves to allow different layers of the object to be in focus. The user looks through the microscope eyepiece. A mirror at the bottom of the microscope reflects light rays up to the object through a hole in the stage. Objective lenses magnify the image which is made even larger when it is seen through the eyepiece lenses. Some light microscopes are actually digital cameras, made to photograph small things but having no eyepiece.

Early monocular light microscope.

Many microscopes, often used in colleges and high schools, normally have a top magnification of 40x with the option of having 4x and 8x. This lets the microscope show basic cells and other items. Others can magnify hundreds of times, or thousands.

Components

Modern monocular transmission microscope, with parts numbered

A microscope objective lens; left 100x, and an eyepiece lens; right 10x

All modern optical microscopes designed for viewing samples by transmitted light share the same basic components of the light path, listed here in the order the light travels through them. Also almost all microscopes have the same 'structural' components:

• Ocular lens (eyepiece) (1)
• Objective turret or Revolver or Revolving nose piece (to hold multiple objective lenses) (2)
• Objective (3)
• Focus wheel to move the stage (4 – coarse adjustment, 5 – fine adjustment)
• Frame (6)
• Light source, a light or a mirror (7)
• Diaphragm and condenser lens (8)
• Stage (to hold the sample) (9)

These entries are numbered according to the image on the right.

Alternatives

Optical microscopes cannot show things that are smaller than light waves, because of the diffraction limit. Microscopes which can see smaller things include:

• Atomic force microscope (AFM)
• Scanning electron microscope (SEM)
• Scanning ion-conductance microscopy (SICM)
• Scanning tunneling microscope (STM)
• Transmission electron microscopy (TEM)
• Ultraviolet microscope
• X-ray microscope

Other websites

• Antique Microscopes.com A collection of early microscopes
• Historical microscopes Archived 2007-04-19 at the Wayback Machine, an illustrated collection with more than 3000 photos of scientific microscopes by European makers (in German)
• The Golub Collection, A collection of 17th through 19th Century microscopes, including extensive descriptions
• Molecular Expressions, concepts in optical microscopy
• Online tutorial of practical optical microscopy
• OpenWetWare
• Antonie van Leeuwenhoek: father of microscopy and microbiology