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 determine why a lens with a large focal length and large aperture is best suited as the objective of an astronomical telescope, we need to understand the role of the objective lens in such telescopes.

1. Light Gathering Power: A large aperture lens collects more light from faint celestial objects, which is crucial for observing stars and dim galaxies. The larger the area of the objective lens, the more light it can gather, enhancing the brightness and visibility of the image. As the option states, "a large area of the objective ensures better light gathering power." Therefore, this statement is correct.
2. Image Quality and Clarity: A larger aperture also improves the quality and clarity of images. It reduces the diffraction effects, allowing for sharper images. This supports the option that says "a large aperture contributes to the quality and visibility of the images."
3. Resolution: The resolution of a telescope, which is its ability to distinguish between two closely spaced objects, improves with an increase in aperture size. A larger aperture provides better resolution, as mentioned in the option "a large aperture provides a better resolution."

Therefore, combining these points, it is clear that all the options listed are interconnected and valid reasons for why a lens with a large focal length and large aperture is best suited for an astronomical telescope. Hence, the answer is "all of the above."