2. CONTENT
What is an eyepiece
Ramsden eyepiece
Spherical aberration
Cromatic aberration
Construction of ramsden eyepiece
Working of ramsden eyepiece
Condition for spherical and cromatic aberration
Mean Focal length
Positive eyepiece
Position of Cross-wire
Cardinal points of Ramsden eyepiece
Merits and Demerits
Difference between huygen's and ramsden's eyepiece
Application of Ramsden's eyepiece
References
3. E Y E P I E C E
Why we need eyepiece ?
The image obtained from
microscopes and telescopes
are not free from optical
defects like cromatic
aberration and spherical
aberration .
We required an instrument
which produce minimum
aberrated image of an object
,and eyepiece is the best for it.
The eyepiece is a magnifier , which is formed by the co-axial system of lenses and are used to
see the minimum abberrated image formed by the objective of optical instrument .
5. JESSE
RAMSDEN
Ramsden was acknowledged to be the most
skillful and capable instrument maker of the
eighteenth century he developed dividing engine
which is the greatest contribution to the
technology of the era By 1789 he had also
produced theodolites, micrometers, balances,
barometers, and the many philosophical
instruments required by the physicists of that
period.
1735 -1800
6. RAMSDEN
EYEPIECE
A Ramsden eyepiece is the simplest
example of an eyepiece for a high
quality optical instrument,
containing two identical plano-
convex lenses. The Ramsden
eyepiece is one of several
eyepiece options when a single
simple magnifying lens is
inadequate due to aberrations. It
is particularly common in
instruments which have a scale or
micrometer wires. It is quite
effective in reducing spherical
aberration , distortion and removes
the problem of coma.
7. SPHERICAL
ABERRATION
Spherical Aberration is an optical problem that occurs when all incoming light
rays end up focusing at different points after passing through a spherical
surface
8. Chromatic aberration is the phenoma in which the lens fails to focus all colours
at the same point which result in multicoloured image of a white object.
CHROMATIC
ABERRATION
9. Ramsden's eyepiece consists of two plano-
convex lenses each of focal length f
separated by a distance equal to (2/3).
The field lens is a little larger than the
intermediate image and is placed close to
this image to allow as much light as
possible to pass through it. The eye lens has
a smaller diameter but carries out the
actual magnification.The objective forms
the real inverted image I1 of a distant
object of eye lens. This serves as an object
for the field lens, which gives rise to a
virtual image I2. in turn serves as an object
for the eye lens. which gives the final image
at infinity, because is made to lie at its
Principal focus.
CONSTRUCTION
OF RAMSDEN
EYEPIECE
10.
11. Image of eye lens is at
Infinity it means object is at focus
WORKING
16. If a cross wire is placed at the I1
position then its magnification is
done by both field lens and eye
lens and their final images obtain
at the same plane.
POSITION OF
CROSS WIRE
26. IT SATISFIES THE CONDITION FOR
ACHROMATISM.
IT IS ACHROMATIC FOR ONLY TWO
CHOSEN COLOURS.
IT IS ACHROMATIC FOR ALL COLOUR
THE OTHER TYPES OF ABERRATIONS
ARE BETTER ELIMINATED. COMA IS
ABSENT AND DISTORTION IS 5%
HIGHER.
THE OTHER TYPES OF ABERRATIONS
LIKE PINCUSHION DISTORTION ARE
NOT ELIMINATED
THE EYE CLEARANCE IS 5% HIGHER
THE EYE CLEARANCE IS TOO SMALL
AND LESS COMFORTABLE.
RAMSDEN HUYGENS
RAMSDEN EYEPIECE IS POSITIVE
EYEPIECE. THE IMAGE FORMED BY
THE OBJECTIVE LIES IN FRONT OF
FIELD LENS. THEREFORE, CROSS-WIRE
CAN BE USED.
HUYGENS EYEPIECE IS NEGATIVE
EYEPIECE. THE IMAGE FORMED BY
THE OBJECTIVE LIES IN BETWEEN THE
TWO LENSES. THEREFORE, CROSS-WIRE
CANNOT BE USED.
THE CONDITION FOR MINIMUM
SPHERICAL ABERRATION IS NOT
SATISFIED. BUT BY SPREADING THE
DEVIATIONS OVER FOUR SURFACES ,
SPHERICAL ABERRATION IS
MINIMIZED.
THE CONDITION FOR MINIMUM
SPHERICAL ABERRATION IS SATISFIED.
IT DOES NOT SATISFY THE CONDITION
FOR ACHROMATISM BUT CAN BE
MADE ACHROMATIC BY USING AN
ACHROMATIC DOUBLET AS THE EYE
LENS.
27. APPLICATIONS
It remains highly suitable for use with
instruments operating using near-
monochromatic light sources e.g.
polarimeters.
The Ramsden eyepiece is still in use today in
astronomical telescopes
Due to the presence of cross wires this
eyepiece is used for taking measurements in
physical science laboratories
Can be used as a simple magnifying glass
Ramsden eyepieces is used in a spectrometer
28. REFERENCES
V. A description of a new construction of eye-glasses for such telescopes as may be
applied to mathematical instruments (royalsocietypublishing.org)
Choosing and Using Astronomical Eyepieces by William Paolini (auth.)
Optics and optical instruments - B.K Johnson
Fundamentals and basic optical lnstruments ; Advanced optical instruments and
techniques by Malacara & Daniel & Thompson & Brian J
Eyepieces (gsu.edu)
Eyepieces - an overview | ScienceDirect Topics
Chromatic Aberration of Eyepieces in Early Telescopes (unl.edu)
Jesse Ramsden - Wikipedia
Eyepiece - Wikipedia
