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A microscope is an instrument for viewing objects that are too small to be seen by the naked or unaided eye. The science of investigating small objects using such an instrument is called microscopy, and the term microscopic means minute or very small, not easily visible with the unaided eye. In other words, requiring a microscope to examine. The most common type of microscope—and the first to be invented—is the optical microscope. This is an optical instrument containing one or more lenses that produce an enlarged image of an object placed in the focal plane of the lens(es).
1 Simple optical microscope
A simple microscope, as opposed to a standard compound microscope (see below) with multiple lenses, is a microscope that uses only one lens for magnification. Leeuwenhoek's microscopes consisted of a single, small, convex lens mounted on a plate with a mechanism to hold the material to be examined (the sample or specimen). This use of a single, convex lens to magnify objects for viewing is still found in the magnifying glass, the hand-lens , and the lupe .
2 Compound optical microscope
The diagrams below show compound microscopes. In its simplest form—as used by Robert Hooke, for example—the compound microscope would have a single glass lens of short focal length for the objective, and another single glass lens for the eyepiece or ocular. Modern microscopes of this kind are usually more complex, with multiple lens components in both objective and eyepiece assemblies. These multi-component lenses are designed to reduce aberrations, particularly chromatic aberration and spherical aberration. In modern microscopes the mirror is replaced by a lamp unit providing stable, controllable illumination.
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- ocular lens or eye-piece
- objective turret, or nosepiece
- objective lenses
- focusThe word focus (pl. foci has several meanings: focus (geometry) focus (optics) See also: autofocus, focal length focus (linguistics) Focus (band) focus (computing) Focus software Ford Focus (automobile) See also focal point (another disambiguation page).ing mechanism
- (may be a fine focus knob)?
- object holder or stage
- mirrorThis article is about the reflective surfaces. A mirror is a reflective surface that is smooth enough to be able to form an image. The best known example is the plane mirror that most people have at home. In it, a parallel beam of light changes its direct
- diaphragm and condenserThe term condenser has the following meanings: In electronics, it is another (more old-fashioned) word for capacitor. In systems involving heat transfer, a condenser is a chamber which converts a substance from its gaseous to its liquid state. In so doing
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Compound optical microscopes can magnify an image up to 1000X and are used to study thin specimens as they have a very limited depth of fieldIn film and photography, the depth of field is the distance in front of and behind the subject which appears to be in focus. For any given lens setting, there is only one distance at which a subject is in focus, but focus falls off gradually on either sid. Typically they are used to examine a smear, a squash preparation, or a thinly sectioned slice of some material. With a few exceptions, they utilize light passing through the sample from below and special techniques are usually necessary to increase the contrastIn visual perception, contrast is the difference in visual properties that makes an object (or its representation in an image) distinguishable from other objects and the background. In visual perception of the real world, contrast is determined by the dif in the imageIn common usage, an image (from Latin imago or picture is an artefact that reproduces the likeness of some subject—usually a physical object or a person. Images may be two-dimensional (e. a photograph) or three dimensional (e. a statue). They are typicall to useful levels (see Contrast methods). Typically, on a standard compound optical microscope, there are three objective lenses: a scanning lens (4x), low power lens (10x), and high power lens (40x). Advanced microscopes often have a fourth objective lens, called an oil immersion lens. To use this lens, a drop of oil is placed on top of the cover slip, and the lens moved into place where it is immersed in the oil. An oil immersion lens usually has a power of 100x. The actual power of magnification is the multiple of the ocular (usually 10x) and the objective lenses being used.
To study the thin structure of metals (see metallography ) and minerals, another type of microscope is used, where the light is reflected from the examined surface. The light is fed through the same objective using a semi-transparent mirror.
