Choosing the Right Microscope
Before choosing the microscope that’s right for your applications, you should be familiar with all the components of a microscope and what function they serve. Below are the basic features and components that all biological microscopes share:
The Stage: Specimens (i.e. objects to be observed) placed on a glass slide and ready for observing are positioned on the microscope’s stage, a smooth, flat surface used to hold the glass slide. On most microscopes the specimen glass remains fixed while the microscope’s objective lens and eyepiece move as a unit up or down to focus the image.
Objective Lenses: A microscope’s objective lens forms the image that is observed with the eyepiece. Different objective lens designs permit different magnifying powers.
Eyepiece: The ocular, or eyepiece, consists of a series of lenses mounted in a barrel and placed in the eyepiece sleeve at the upper end of the microscope. Eyepieces of varying powers work with objective lenses of varying powers to yield a range of microscope magnifications.
Magnification: The effective magnification of a microscope is determined by multiplying the eyepiece power by the objective lens power. Thus a 40X objective lens used with a 10X eyepiece presents an effective magnification of 400X to the observer. Lower magnifying powers allow for brighter, sharper images combined with a wide field of view; higher powers, often useful in specific observing situations, present larger but dimmer images with narrower fields of view. When observing a specimen, always begin at lower powers, progressively increasing to higher magnifications.
Focusing: Most microscope models include a focusing control for quick focusing of the image. More advanced models include both coarse and fine focusing controls; the fine focus is particularly advantageous in high-power applications.
Light Source: Used to illuminate the specimen, adjustable mirrors reflect an external light source into the microscope’s specimen observing area. Some models utilize built-in light sources to provide direct and intense object illumination at high powers.
Condensing Lens: Sub-stage condensing lenses concentrate light on to the specimen. A rotary variable-aperture diaphragm permits varying illumination intensities.