Optical instruments like magnifying glasses, cameras, microscopes and telescopes extend the capabilities of the human eye. Magnifying glasses allow close examination of small objects like stamps. Cameras can capture events over time like photojournalists do. Microscopes enable the study of tiny organisms. Telescopes help astronomers observe distant heavenly bodies. These tools use lenses or mirrors to enlarge and clarify images beyond the limits of normal vision.

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Your eye is a very effective organ, but its ranged can be
extended in a lot of ways by means of optical instruments such as:
magnifying glasses, cameras, microscopes and telescopes.
Stamp collectors use magnifying glasses to look closer into
their collection. Photojournalist are able to “stop time” and capture
a certain event using cameras. Biologist can see and study small
entities such as microbes and bacteria using a microscope.
Astronomers can probe the heavenly bodies using telescope. These
and many others, are just some of the technologies that help your
eyes to investigate everything around you.

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Magnifying Glass
Magnifying glasses are simple instruments used to enlarge objects.
They consist of a single, biconvex lens mounted in a frame with a handle.
Camera
The camera is used to capture images to a medium and store it
over a period of time. A simple camera follows the same mechanism as
the human eye. The major parts of the eye used in vision, the lens, iris,
and the retina, correspond to the major parts of a camera: the lens,
aperture, and the focal plane.

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Microscope
A microscope is an optical instrument for viewing objects that are
too small to be seen by the naked eye or unaided eye. The simplest
microscope is the compound microscope that uses two converging lens
used to magnify objects: the objective and the eyepiece lenses.
The objective lens forms a real and enlarged image, while the eyepiece
forms final and virtual image. The objective lens regulates and forms an
enlarged real image which is viewed through the eyepiece.

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Telescope
Is a device that gathers light or electromagnetic waves and focuses it
to form an image.
It is commonly used to make far away objects, like the planets of our solar
system, seem closer. There are two main types of telescopes: refracting
and reflecting telescopes. The difference depends on the components
used to observe distant objects.
The refracting telescope or refractor is a type of optical telescope
that uses lens as its objective to form object. It uses refraction to make
distant objects appear closer and more visible.

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These are usually made up of two lenses: the objective lens (larger lens)
and the eyepiece lens(smaller lens). This uses the same principle as the
optical microscope. However, the object is effectively placed at infinity
instead of putting the object near the object lens.
The reflecting telescope, or reflector has a concave mirror that
gathers light from the object and focuses it into an adjustable eyepiece
or combination of lenses through which the reflection of the object is
enlarged and viewed.

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• Myopia (Nearsightedness) – A myopic or nearsightedness person sees
clearly but far objects appear blurred to him/her.
• Hyperopia(Farsightedness) – A hyperopic person sees distant objects clearly
but see nearly objects appear blurred to him/her.
Some Common Eye Defects

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• Astigmatism – It is an eye defect in which the surface of the cornea is not
spherical, but it is more sharply curved in one plane than another.
• Presbyopia – This eye condition is common among people who reach
middle age. Unlike farsightedness, this condition produces blurred images of
near objects because of a decrease in ability to focus on light and nearly
objects due to weakening of the ciliary muscles and the hardening of the
lens.
Some Common Eye Defects

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