OPTICAL LENS
An optical lens is a single, optically transparent device shaped/designed to allow the
transmission and refraction of light to create a specific and controlled optical outcome.
An optical lens is distinct from a photographic lens. The latter integrates both mixed lens
elements and various mechanisms to create a complex optical unit for photography.
Types of optical lens
Lenses come in a broad range of types. However, in general.
● A converging lens is called a convex lens.
● A diverging lens is called a concave lens.
Lens, in optics, piece of glass or other transparent substance that is used to form an image of an
object by focusing rays of light from the object.
An optical lens is a transparent optical component used to converge or diverge light emitted
from a peripheral object. The transmitted light rays then form a real or virtual image of the
object. Lenses are a good example of transmissive optical components, meaning that they pass
or transmit light.
Refraction – changing the shape of the image
Lenses work by bending rays of light to meet at a focus point. An optical lens is able to bend
light by a phenomenon called refraction. When a light wave changes from one medium to
another (eg. from air to glass) the light wave will change direction at the contact surface. When
the rays of light bend by refraction this changes the characteristics of the image created by the
lens. The apparent size and shape of the image can be changed in this way.
Principle rays
Lens diagrams show lines (rays) following the possible scenarios for the way light passes though
the lens. Each shows the refraction route of that ray. The diagram also shows how the focal
point is derived.
The optical lens has two focus points. The principle focus point is where the light focuses to a
point for a converging lens. In the case of a concave (diverging) lens the principle focus point is
a virtual (or back-projected) point shown on the diagram before the lens (see the diverging lens
diagram further on). This is shown as a dotted line since it is not an actual ray path.
In the case of a converging lens (convex) the rays all end up at the ‘real’ image in the same
place. The total sum of the light entering the lens ends up projected onto the image plane. For
a diverging lens (concave) the rays are refracted out wider than the incoming rays and never
focus to a point.
Advantages & Disadvantages of Optical lenses
Construction and materials
Lenses are normally, but not necessarily, transparent. Some may be translucent for very
specialist use, or transparent to particular forms of electromagnetic radiation but opaque to
vision.
Lenses for optical purposes are normally, but not always made of glass. Very cheap disposable
cameras may have plastic lenses. Magnifying optical lenses may also be of plastic. Lenses for
non-visible forms of electromagnetic radiation may be made out of a variety of non-glass
substances. They may also be optically opaque.
The different materials that optical glass is made from have different refraction characteristics.
So more than one type of glass could be used in one photographic lens. For example, some
lenses cause chromatic aberrations. However, a paired lens of a different material can be used
to counteract that aberration.
In general optical lens elements with higher quality optical glass have ultra-low light dispersion
characteristics. The glass itself tends to be harder than lower quality glass too. These glasses are
made from expensive chemicals and the harder they are the more firing (heat treatment) and
grinding (shaping and polishing) is involved in creating the final lens. For these reasons high
quality glass optical lenses are expensive. The cost goes up significantly for higher quality
grades.
Application of Optical lenses
● Photographic camera lenses
● Magnifying glass
● Contact lenses
● Eye glass
● Flash lights
