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Microscope

A compound microscope has two lenses: an eyepiece lens and objective lens. The eyepiece lens usually has a magnification of 10X. There are objective lenses on the revolving nosepiece with varying magnifications. Most compound microscopes have objective lenses with magnification of 4X, 10X, and 40X. Some compound microscopes also have an oil immersion lens with a magnification of 100X.

The usual magnification of an ocular lens on a compound microscope is 10X. Some microscopes have a 15X eyepiece lens. The ocular lens is the lens at the top of the tube, the one that you first look through when using a microscope. It is also called the eyepiece lens.

To calculate the total magnification achieved with a compound microscope, the magnification of the ocular lens is multiplied by the magnification of the objective lens. For example, if viewing a sample with the 40X objective, the total magnification would be calculated as follows: a 10X ocular lens used with a 40X objective lens, the total magnification is 400X (10 x 40).

With light microscopy, there normally is a space of air between the slide and the lens. Oil immersion replaces that space of air with oil. The refractive index of the oil is the same as glass.

The role of the condenser lens is to focus light on the specimen. It is used with higher magnifications.

Resolving power is the ability to see two things as discrete images. With normal vision, there is a resolving power of about of 100 micrometers. A compound microscope has a resolving power of approximately .2 micrometers. In other words, two marks .2 micrometers apart can be seen as two distinct entities. Any closer than this, they are perceived as one object.

The base is the bottom of the microscope. The revolving nosepiece is also called a turret. The objective lens are attached to the nosepiece (or turret). The slide rests on the stage. The tube is the structure which connects the eyepiece to the objective lenses (it is shaped like a tube; thus, its name). The diaphragm controls the diameter of the cone of light.

Parafocal is the term used for a microscope if the focus knob does not have to be readjusted when changing the magnifications. This phenomenon is seen with good compound microscopes. In other words, when the specimen is in focus at 4X and the objective is switched to 10X, the specimen remains in focus.

A simple microscope has only one lens. A compound microscope utilizes two lenses: an ocular lens and an objective lens. The compound microscope is also referred to as a "light microscope" or "bright field microscope". A phase contrast microscope is useful for examining living cells, because the specimen does not need to be stained. A dissection microscope uses low power magnification. Things appear three dimensional with a dissection microscope. A transmission electron microscope does not use light, but rather a beam of electrons.

 

 
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