Why are there multiple lenses cemented together to form the objective lens and the eyepiece lens?

The reason for having multiple lenses cemented together to form the objective lens and the eyepiece lens is due to the limitations of a single lens in achieving the desired optical properties.

To understand this better, let's take a closer look at both lenses:

1. Objective Lens: The objective lens is positioned at the front end of a telescope or microscope and collects light from the object being observed. It is responsible for forming the initial image of the object. Multiple lenses are combined to form the objective lens to overcome certain optical aberrations.

Optical aberrations, such as chromatic aberration (where different colors focus at different points) and spherical aberration (where light does not focus to a point but forms a blurry spot), can be minimized by combining lenses with different shapes and properties. By using multiple lenses, each lens can compensate for the particular aberrations introduced by the previous lens, resulting in a clearer and more accurate image formation.

2. Eyepiece Lens: The eyepiece lens is positioned at the opposite end of the objective lens and is responsible for magnifying the image formed at the objective lens. Similar to the objective lens, the eyepiece lens may consist of multiple lenses.

The main purpose of combining lenses in the eyepiece is to achieve a wider field of view and a more comfortable viewing experience. The eyepiece lens system helps correct various aberrations that would otherwise distort the image or reduce the clarity of the view.

By carefully selecting and arranging multiple lenses, optical designers can control and correct specific aberrations, resulting in a clearer, sharper, and more accurate image for the viewer.

In summary, the use of multiple lenses cemented together in the objective lens and the eyepiece lens helps overcome various optical aberrations, leading to improved image quality and a better viewing experience.