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Optical instruments
Chapter Six

Optical Instruments

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Introduction

Optical instruments enhance the human eye’s ability to see distant and tiny objects,
making it possible to observe stars and microorganisms that are otherwise invisible.
These devices use light, along with lenses, mirrors, and prisms, to form clearer
images. In this chapter, you will learn how various optical instruments work,
including microscopes, telescopes, and cameras. The competencies developed
will enable you to choose, use, and even construct simple optical instruments for
different applications.

Think
Life without optical instruments

Simple microscope to the near point of the eye increases the
The size of an object as viewed by the size of the image on your retina. But if you
eye is determined by the size of its image still move the object closer than the near
formed on the retina. The size of the point, the image will be fuzzy or blurred
image depends on the distance from the because the lens of the eye will no longer
object to the observer’s eye and the angle focus an image on the retina. Therefore,
subtended by the object at the eye, called the closest comfortable distance for
angular size (θ). If you want to look viewing an image is when an object is
closely at a small object, such as an insect, at this point. Thus, an object cannot be
you bring the object close to your eye. By brought closer to the eye beyond the
doing so, you increase the angular size near point. To overcome this limitation, a
and hence make the image on the retina converging lens can be used to enlarge the
as large as possible. However, your eyes image of an object. The object can then be
cannot focus sharply on objects that are moved even closer to the eye, resulting in
closer than a point at about 25 cm from a large image formed on the retina. A lens
the eye. This point is known as the near used in this way forms a device known as
point of the eye. Moving an object closer a simple microscope.

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