Question

1. In terms of edges, why is it an advantage to use mirrors over lenses in telescopes?

2. How does the placement of the eyepiece with Newtonian and Cassegrain reflectors differ?

3. What does the diffraction limit of a telescope depend upon?

Answer 1

1- Advantage of using mirror,

(i) Reflecting telescopes use mirrors instead of lenses to collect light. Because mirrors have only one reflective surface, they are easier to construct than lenses, which are made from optical glass, and cannot have any occlusions because light must pass completely through them.

(ii) Mirrors have less spherical aberration, which is a scattering of light that occurs when lenses don't perfectly focus on a single point.

(iii) Mirrors also reflect all wavelengths of light equally, whereas lenses bend light differently depending on its wavelength.

Edge or Size Advantage-

(i) Mirrors are easier to construct than lenses, they can be made larger and more durable.

(ii) Because only one side of the mirror is used to focus the light, the other side can be placed against a surface for support. This allows for the mirror to be extremely large as compared to a lens, and makes them ideal for observing space. The larger the collection device, the more light can be directed to the eyepiece.

Therefore, largest optical telescopes in the world, including the largest one at the Keck Observatory in Hawaii, are reflecting telescopes.

2.

Placement of eyepiece on Newtonian reflector, is on the side of telescope.

While, Placement of eyepiece on the Cassegrain reflector, is on the bottom.

Here is diffrence shown in respective pictures,

(i) Newtonian reflector,

(ii) Cassegrain reflector,

3.

Diffraction limit of telescope= 1.22*wavelength(in cm)/ diameter(in cm)

Therefore, Diffraction limit of telescope is inversely related to the diameter of the telescope's objective.

So as the diameter increases, diffraction limit goes down. Hence you can resolve objects clearly with larger telescopes.