In the preponderance of cases, the primary reason for introduction of an optical system to be used with the eye is to increase the size of the final image on the retina, thus allowing the viewer to resolve greater detail within that image than would be possible with the naked eye. The term for this increase of final image size is magnification. While frequently used when describing the function of an optical device or system, the term magnification is often misinterpreted or applied incorrectly. This chapter contains information and examples that will allow the reader to better understand the true meaning and proper application of the term magnification.
A near object is one that can be placed at a comfortable distance from the eye for purposes of visual examination. In order to discuss the magnification factor introduced by an optical system it is essential that we first establish a reference case for comparison purposes. For that reference case, let's consider the typical unaided eye, accommodated to view an object at the near point of vision, which is 254 mm (10 inches).
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