Question

A lens of large focal length and large aperture is best suited as an objective of an astronomical telescope since:

• A. a large aperture contributes to the quality and visibility of the images.
• B. a large area of the objective ensures better light gathering power.
• C. a large aperture provides a better resolution.
• D. all of the above.

Answer 1

The Correct Option is D

To answer why a lens with a large focal length and large aperture is best suited as an objective of an astronomical telescope, let's examine the concepts involved:

1. Light Gathering Power:

   A large aperture means a larger area through which light enters the telescope. This increases the light gathering power of the telescope, allowing it to collect more light from faint and distant celestial objects. This can be particularly critical for observing distant stars, galaxies, and other astronomical phenomena.

2. Image Quality and Visibility:

   The quality and visibility of the images are enhanced with a large aperture because more light can be collected. This results in brighter images with enhanced details. A lens with a large focal length can also result in a higher magnification for viewing distant objects.

3. Resolution:

   Resolution refers to the telescope's ability to distinguish fine details and two points in an object. A large aperture provides better resolution, reducing the effects of diffraction, which allows for finer details to be resolved. This is essential for distinguishing between closely spaced objects in the sky.

Thus, all the choices contribute to making a large focal length and large aperture lens desirable for an astronomical telescope. This is why the correct answer is:

All of the above: A large aperture contributes to quality and visibility of the images, better light gathering power, and better resolution.