Question:

Two different lenses are used in telescope because

Updated On: Apr 28, 2025
  • Magnification is increased
  • Focal length is increased
  • More light is captured
  • Spherical aberration is increased
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The Correct Option is A

Solution and Explanation

Two different lenses are used in a telescope to increase the effective focal length of the system while maintaining a reasonable level of image quality. The objective lens, or primary lens, is typically a large lens with a long focal length that captures light from a distant object and forms a real image. The eyepiece lens, or secondary lens, is a smaller lens placed near the focal point of the objective lens and is used to magnify the real image formed by the objective lens.
By using two lenses, the effective focal length of the telescope is increased, allowing for greater magnification of distant objects. This also enables the observer to see finer details of the object being observed. Additionally, using two lenses reduces spherical aberration, which can occur when using a single lens with a large aperture, leading to a clearer and more detailed image.
Answer. A

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Concepts Used:

Optical instruments

A device that processes light waves (or photons), either to enhance an image for viewing or to analyze and determine its characteristic properties is called an optical instrument (or "optic" for short).

Applications of Optical Instruments:

  1. Microscope - It is one of the most extensively used optical instruments comprised of only one lens or combination of the lenses for magnifying and inspecting bodies that are too small to be seen in detail by clear eyes. Earlier microscopes had only one lens, and are, therefore, called simple microscopes, but the present microscopes are accessible with at least two lenses and thereby, termed a compound microscope.
  2. Telescope - It is another remarkable optical instrument. It makes distant objects emerge nearer by using an arrangement of lenses or lenses and curved mirrors that is used to observe the objects by absorption, emission, and reflection of their electromagnetic radiation to furnish a magnified image. As they are used to view objects that are far away, they include at least two lenses.