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microscopeInvented by a Dutch spectacle maker in the late 16th century, light microscopes use lenses and light to magnify images. Although a magnifying glass technically qualifies as a simple light microscope, today’s high-power—or compound— microscopes use two sets of lenses to give users a much higher level of magnification, along with greater clarity. The first set of lenses are the oculars, or eyepieces, that the viewer looks into; the second set of lenses are the objectives, the lenses closest to the object (specimen). Before purchasing or using a microscope, it is important to know the functions of each part.

Eyepieces: The eyepieces are the lenses at the top that the viewer looks through; they are usually 10X or 15X. To get the total magnification level, multiply the magnification of the objective used (ex: 10X eyepiece * 40X objective = 400X total magnification).

Tube: Where the eyepieces are dropped in. Also, they connect the eyepieces to the objective lenses.

Base: The bottom of the microscope—what the microscope stands on.

Arm: Structural element that connects the head of the microscope to the base.

Stage: The flat platform that supports the slides. Stage clips hold the slides in place. If your microscope has a mechanical stage, the slide is controlled by turning two knobs instead of having to move it manually. One knob moves the slide left and right, the other moves it forward and backward.

Illuminator: A steady light source (110 volts in the US) that shines up through the slide. Mirrors are sometimes used in lieu of a built-in light. If your microscope has a mirror, it is used to reflect light from an external light source up through the bottom of the stage.

Nosepiece: This circular structure is where the different objective lenses are screwed in. To change the magnification power, simply rotate the turret.

Objective Lenses: Usually you will find 3 or 4 objective lenses on a microscope. The most common ones are 4X (shortest lens), 10X, 40X and 100X (longest lens). The higher power objectives (starting from 40x) are spring loaded. Spring loaded objective lenses will retract if the objective lens hits a slide, preventing damage to both the lens and the slide. All quality microscopes have achromatic, parcentered, parfocal lenses. In addition, to get the greatest clarity at high levels of magnification, you will need a microscope with an Abbe condenser. Lenses are color coded and are interchangeable between microscopes if built to DIN standards.

Rack Stop: This feature determines how far up the stage can go. Setting the rack stop is useful in preventing the slide from coming too far up and hitting the objective lens. Normally, this adjustment is set at the factory, and changing the rack stop is only necessary if your slides are exceptionally thin and you are unable to focus the specimen at higher powers.

Condenser Lens: Condenser lenses focus the light that shines up through the slide, and are useful for attaining sharp images at magnifications of 400X and above. If the maximum power of your microscope is 400X, a stage mounted 0.65 NA (or greater) condenser is ideal since it give you greater clarity without having to be focused separately. However, if your microscope goes to 1000X or above, focusable condenser lens with an N.A. of 1.25 or greater is needed. Most microscopes that go up to 1000X come equipped with an Abbe condenser, which can be focused by moving it up and down. The Abbe condenser should be set closest to the slide at 1000X, and moved further away as the magnification level gets lower.

Diaphragm or Iris: The diaphragm or iris is located under the stage and is an apparatus that can be adjusted to vary the intensity, and size, of the cone of light that is projected through the slide. As there is no set rule on which setting to use for a particular power, the setting depends on the transparency of the specimen and the degree of contrast you desire in your image.

What to look for when purchasing a microscope: If you want an instrument that can provide you with crisp, high-quality images at high resolutions, stay away from microscopes with plastic components. Instead, look for a microscope that has a metal body and all glass lenses. Make sure you purchase your precision instrument from a well-established dealer who will be around to help you with technical problems in case you have issues with your microscope. At AmScope.com, we pride ourselves on providing the best instruments at the lowest prices without sacrificing customer service. Technical support is one simple phone call or email away.