What Is the Meaning of Objective Lens?
The term "objective lens" refers to a part of a compound microscope. The objective lens hangs directly above the viewing area and transmits an enlarged image of the object under examination through the microscope tube. It is called an "objective lens" because the lens hangs directly above the object under investigation.
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Compound Microscopes
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The defining characteristic of a compound microscope is that it combines, or compounds, the optical effects of two different lenses. These two lenses are called the ocular and the objective lens.
Ocular Lens
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The ocular lens is located at the top of the microscope tube. This is the lens that the viewer places his eye up to when looking into the microscope. To change the magnification level of the ocular lens, the user replaces the entire eyepiece.
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Objective Lens
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The objective lens is located at the bottom of the microscope tube, directly above the object being viewed. Most compound microscopes have multiple objective lenses that are affixed to a rotating base to allow the user to swap them in and out to change the magnification level.
Magnification Level
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Because a compound microscope has two lenses working together, the overall magnification equals the ocular magnification multiplied by the objective magnification. One common design for compound microscopes has objectives at 10x, 45x and 100x magnification levels. With lower power objectives, a 10x ocular lens is used. High power objectives, which must be used with oil-immersion slides, are paired with either a 5x or 7x ocular lens.
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References
- Photo Credit microscope image by Aleksej Kostin from Fotolia.com
