1. LENSES
• A lens is an optical device, which transmits and
refracts lights, converging or diverging the
beam.

2. HISTORY
• The word lens comes from the Latin name of
the lentil, because a double-convex lens is lentilshaped.
• The genus of the lentil plant is lens , and the
most commonly eaten species is Lens culinaris.
• The oldest lens artifact is the Nimrud Lens,
dating back 2700 years to ancient Assyria.
• David Brewster proposed that it might have been
used as a magnifying glass, or as a burningglass to start fires by concentrating sunlight.

3. A Nimrud Lens

4. • Another early reference to magnification dates back
to ancient Egyptian hieroglyphs in the 8th century
BC, which depict "simple glass meniscal (a lens with
the convex face facing outward.) Lenses“
• The earliest written records of lenses date to Ancient
Greece, with Aristophanes' play The Clouds (424 BC)
mentioning a burning-glass (a biconvex lens used
to focus the sun's rays to produce fire).
• Some scholars argue that the archeological
evidence indicates that there was widespread use of
lenses in antiquity, spanning several millennia.
• These lenses were used by artisans for fine work,
and for authenticating seal impressions.

5. Ancient lens
One used by artisans

6. • The writings of Pliny the Elder (23–79) show that
burning-glasses were known to the Roman
Empire, and mentions what is arguably the
earliest written reference to a corrective
lens: Nero was said to watch the gladiatorial
games using an emerald .
• Both Pliny and Seneca the Younger (3 BC–65)
described the magnifying effect of a glass globe
filled with water.

7. TYPES OF LENSES
A simple lens consists of a
single optical element.
A compound lens is an
array of simple lenses
(elements) with a
common axis; the use of
multiple elements allows
more optical
aberrations to be
corrected than is possible
with a single element.
Lenses are typically made
of glass or transparent
plastic.
The Visby lenses or Viking
lenses

8. WHAT ARE VIKING LENSES ???
• The Visby lenses or Viking lenses are a collection of lensshaped manufactured objects made of rock
crystal (quartz) found in several Viking graves on the island
of Gotland, Sweden, and dating from the 11th or 12th
century.
• Some were in silver mounts with filigree.
• It has been suggested that the lenses themselves are
much older than their mounts.
• The symmetry of the lenses as well as their biconvex
elliptical form and fine polish, which resulted in a very
good imaging, made a sensation when discovered by
modern scientists.
• The Viking lenses were capable of concentrating enough
sunlight to ignite fires.

9. Uses Of Viking Lenses…
• Used in jewellery
• used by craftsmen for magnification in fine
work
• used as reading stones
• also to start fires.
• Olaf Schmidt has speculated that they may
have been used as part of a telescope

10. A Viking lens

11. WHAT ARE SIMPLE LENSES???
• A simple lens or singlet lens is a lens consisting
of a single simple element.
Types of Singlet Lenses

12. Classification of LENSES…
• Lenses are classified by the curvature of the two optical
surfaces.
• A lens is biconvex (or double convex, or just convex) if both
surfaces are convex.
• If both surfaces have the same radius of curvature, the
lens is equiconvex.
• A lens with two concave surfaces is biconcave (or just
concave).
• If one of the surfaces is flat, the lens is Plano-convex or
Plano-concave depending on the curvature of the other
surface.
• A lens with one convex and one concave side is convexconcave or meniscus.

13. Some basic instructions…
• The distance from the lens to the spot is the focal
length of the lens, which is commonly abbreviated f in
diagrams and equations.
• The point of incidence is that point on the surface of the
mirror where the incident ray falls. A line perpendicular to
the surface, at the point of incidence , is known as Normal.
• The ray of light coming towards the mirror is called the
Incident Ray.
• The ray of light which turns back after ‘reflection’ is called
the Reflected Ray.
• The angle between the incident ray and the normal at the
point of incidence is known as the Angle of Incidence.
• The angle between the normal and the reflected ray at the
point of incidence is called the Angle of Reflection.

15. Application of these lenses…
• If the lens is biconvex or Plano-convex,
a collimated beam of light passing through the
lens will be converged (or focused) to a spot
behind the lens. In this case, the lens is called
a positive or converging lens.

16. • If the lens is biconcave or Plano-concave, a
collimated beam of light passing through the lens is
diverged (spread); the lens is thus called
a negative or diverging lens. The beam after passing
through the lens appears to be emanating from a
particular point on the axis in front of the lens.

17. • Convex-concave (meniscus) lenses can be either
positive or negative, depending on the relative
curvatures of the two surfaces. A negative
meniscus lens has a steeper concave surface and will
be thinner at the centre than at the periphery.
• A positive meniscus lens has a steeper convex
surface and will be thicker at the centre than at the
periphery.
• An ideal thin lens with two surfaces of equal
curvature would have zero optical power, meaning
that it would neither converge nor diverge light.
• All real lenses have nonzero thickness, which causes
a real lens with identical curved surfaces to be
slightly positive.
• To obtain exactly zero optical power, a meniscus lens
must have slightly unequal curvatures to account for
the effect of the lens' thickness.

18. Lensmaker’s Equation
• The focal length of a lens in air can be calculated
from the lensmaker's equation:
Where,
is the power of the lens,
is the focal length of the lens,
is the refractive index of the lens material,
is the radius of curvature of the lens surface closest to the light source,
is the radius of curvature of the lens surface farthest from the light source, and
is the thickness of the lens (the distance along the lens axis between the two surface
vertices).

19. Thin Lens Equation
• If d is small compared to R1 and R2, then the thin
lens approximation can be made. For a lens in
air, f is then given by