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Types of Compound Light Microscope Objectives

The compound light microscope has a number of different objective lenses which allow for different degrees of magnification. Being able to differentiate between the different lenses and having a general idea of the level of detail that can be seen with each magnification will help a great deal when examining samples under the microscope.

  1. Scanning Objective Lens

    • Most objective lens are color-coded, including scanning objective lenses. Scanning objective lenses usually have a red band around them and provide a magnification of 4x. The purpose of this lens is to provide an initial magnification of the specimen being studied. Although the scanning lens does not provide a great deal of magnification, it is important to use this lens with every specimen to initially bring it into focus and center it within the field of view.

    Low Power Objective Lens

    • Low power objective lenses typically provide a 10x magnification and will have a yellow band around them. Low power objective lenses are usually rotated into place after the scanning objective lens and provide additional magnification of the specimen being studied. The low power lens is useful for observing a large group of cells under the microscope or gaining general information about the structure of a small organism.

    High Power Objective Lens

    • The high power objective lens of a microscope usually provides a magnification of 40x, although different lenses can provide a range of different magnifications from 20x to 200x. If the lens has a 40x magnification, it will usually have a blue band around it. A high power objective lens can be used either after the scanning objective lens or low power objective lens and provides a great level of detail of the specimen being observed.

    Oil Immersion Lens

    • Most oil immersion lenses have a magnification of 100x and have a white band around them. Oil immersion lenses use special oil to improve the resolution of the image produced by the lens. A small drop of oil is placed between on the top of the cover slip of the slide before the lens is rotated into place. With this degree of magnification, properties of an individual cell can be observed when combined with appropriate staining techniques.

    Considerations

    • When deciding which lens to use, consider the level of detail that needs to be observed. Always start with the scanning objective lens to initially focus and center the specimen before rotating the desired lens into place. When using a high power or oil immersion lens, only use the fine focus adjustment knob to avoid breaking the slide or damaging the lens. Be sure to clean lenses with lens paper only, since other materials can scratch the lens.

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