In this term paper most of the types of lens aberrations have been discussed and also have discussed about the use of this knowledge. The aberrations covered in this presentation are:- Monochromatic Aberrations--Spherical Aberration, Coma, Field Curvature, Distortion, Astigmatism. Chromatic Aberrations - Longitudinal Chromatic Aberrations and Transverse Chromatic Aberrations.

1. PHYSICS TERM PAPER
TOPIC:-LENS ABERRATIONS

2. LENS ABERRATIONS
 In optical system all rays
from a point in the
object plane would
converge to the same
point in the image plane.
 The influences which
cause the different rays
to converge to different
points are called
aberrations.

3. MONOCHROMATIC
ABERRATIONS CHROMATIC ABERRATIONS
 These are those aberrations
which include only one type
of wavelength.
 It includes following
aberrations:-
 Spherical Aberrations
 Coma
 Field Curvature
 Distortion
 Astigmatism
 These are those aberrations
which occur due to different
bending of different
wavelengths for same
refractive index.
 It includes following
aberrations:-
 Longitudinal Chromatic
Aberrations
 Transverse Chromatic
Aberrations

4. SPHERICAL ABERRATIONS
 It occurs due to the
improper refraction of
the light rays when
they strike a lens near
its edge, in comparison
with those striking near
to the centre.
 This aberration is
termed as positive
spherical aberration
when rays are bending
too much.
 And negative
aberration when
bending of rays is not
enough.

5. APLANATIC POINT
1) A spherical lens
has an aplanatic
point(i.e. no
spherical aberration)
only at a radius
equals the radius of
the sphere divided
by the refractive
index of the lens
material.
2) For a normal
glass this value is
43% i.e. 67% of
diameter of a
spherical lens is
useful.

6. IMAGE FORMED IN SPHERICAL
ABERRATION
• Upper row is of negative
aberration
• Middle one is zero aberration
• Lower one is the positive
aberration

7. COMA
 Coma is an aberration
that afflicts off-axis light
bundles in a manner
quite similar to the way
in which spherical
aberrations affects the
axial bundles.
 This result in an overall
spot that is comatic in
shape, having bright
central core with a flare
extending towards the
optical axis of the lens.

9. FIELD CURVATURE
 Most optical tend to form the
image on a curved surface.
 The nominal curvature of this
surface is reciprocal of the
radius of the lens and this is
referred to as the Petzval or
field curvature of the lens.
 This error arise due power
error for rays at a larger
angle.
 These rays strike the lens as
having an effectively smaller
diameter and an effective
high power, forming the
image of the off axis points
closer to the lens.

12. ASTIGMATISM
 In this the rays that
propagates in two
perpendicular
planes have
different foci.
 If an optical system
with astigmatism is
used to form an
image of a cross,
the vertical and
horizontal lines will
be sharp but at
different distances.

13. TYPES OF ASTIGMATISM
 First one is third order
aberration, occurs for
objects away from optical
axis.
 This form of aberration
occurs even when the
optical system is
symmetric.
 The second form occurs
when the optical system
is not symmetric about
the optical axis.
 Occurs due to
manufacturing error or
misalignment of
components.

15. IMAGE DISTORTION
 It is the deviation from
rectilinear projections. Means
projection of straight line is
not straight line.
 Barrel Distortion:- Image
magnification decreases with
distance from the optical axis.
 Pincushion Distortion:-Image
magnification increases with
the distance from the optical
axis.
 Moustache Distortion:-
Combination of above types.
It starts with barrel distortion
at the centre and gradually
turns to pincushion distortion
at the periphery. The resultant
image looks like a handlebar
moustache.

16. Moustache Distortion

17. CHROMATIC ABERRATIONS
 It is an effect resulting from
dispersion in which there is
failure of lens to focus all
colours to some
convergence point.
 It has two main types:
 Longitudinal:-occurs when
different wavelengths focus
at different distances from
lens.
 Transverse:-occurs when
different wavelengths are
focused at different positions
in the focal plane because
magnification of the lens also
varies with wavelength.

18. LONGITUDINAL TRANSVERSE
IMAGE IN CHROMATIC ABERRATIONS

19. CORRECTIONS AND
APPLICATIONS
 Spherical aberrations,
field curvature can be
corrected by the use of
combination of different
lenses or by use of
aspherical lenses or by
use of stops.
 Chromatic aberrations
can be removed by the
use of the achromatic
lens. The other option is
the use of two mated
lens-concave and
convex.
 Astigmatism can be
removed by the use of
pantoscopic tilt
glasses.
 Coma can be
minimized by using a
complex lens system or
by pair of lenses
arranged symmetrically
as in a relay lens
system.

20. WHERE WE ARE USING THIS
KNOWLEDGE(APPLICATION)
• To make telescope, microscope the appropriate
lenses need to be selected so their knowledge is
necessary.
• The elimination techniques of coma are used in
designing of many lenses for instruments like
borescopes and submarine periscopes.
• In making of camera lenses, high resolution optical
devices, making of correctors and the most
important the human eye which also contains a
convex lens. So, this knowledge is also important for
the correction of are eyes.

21. THANK YOU