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Ramsden's Eyepiece And its Applications
- 1. RAMSDEN EYEPIECE AND ITS APPLICATION
- 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 .
- 4. HUYGEN EYEPIECE Ramsden eyepiece There are two major types of eyepieces that are grouped according to lens and diaphragm arrangement:
- 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
- 11. Image of eye lens is at Infinity it means object is at focus WORKING
- 12. SPHERICAL ABERRATION CONDITION: d= f1-f2 In Ramsden eyepiece f1=f f2=f therefore d=f-f =0 So ,spherical abrerration is present in ramsden eyepiece
- 13. CONDITION: therefore, CHROMATIC ABERRATION f1=f2=f So, chromatic aberration is present in ramsden eyepiece
- 15. POSITIVE EYEPIECE In this eyepiece magnification of the real image of the objective lens is done so this eyepiece is positive eyepiece.
- 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
- 29. YOU THANK