Question

Why do we prefer a Ramsden's eyepiece toa Huygens' eyepiece?
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Answer 1

To be explored: Why do we prefer a Ramsden's eye piece to a Huygen's eye piece.

Answer:

• Eye piece: Eye piece is a lens or combination of lenses used in an optical instrument, through which eye views the image formed in front of the lens.
• Usually, it is a combination of two lenses, out of which, one will be nearer to the eye and is termed as "eye lens". The other one is nearer to the primary image and is termed as "field lens".
• Sometimes, an eye piece is used as a magnifier.
• Two forms of eye piece that are still in use are Ramsden's eye piece and Huygen's eye piece.
• Ramsden's eye piece is an eye piece consisting of two plano-convex lenses of equal focal length, in which the convex sides face each other, with a separation of 2/3 of the focal length between the lenses.
• In Ramsden's eye piece, the primary image forms in front of the field lens, where a scale can be placed for measurements.
• In the Huygen's eye piece, the primary image is formed behind the field lens. Here, a scale or cross-hairs cannot be used for any measurements.
• Also, Ramsden's eye piece provides higher degree correction for spherical aberration, unlike the Huygen's eye piece.

Hence, Ramsden's eye piece is preferred to a Huygen's eye piece.