Spherical lens foci

The lenses used in eyeglasses help correct vision problems

In our studies we defined spherical lenses as an association of two diopters in which one of them is spherical and the other can be spherical or flat. We also saw that the spherical lens is nothing more than an optical system formed by three homogeneous and transparent media.

Like many other subjects in Physics, Optics is also present in our daily lives. As an example of its use, we have the figure above, where the spherical lens is being used to correct a visual problem. There are several other examples of its use, such as in cameras, telescopes, etc.

Spherical lenses can be classified into converging lenses and diverging lenses. In a converging lens, parallel light rays arriving at the lens surface are directed, i.e., converge, to a single point in space. In diverging lenses, parallel light rays are scattered, that is, they diverge to a single point.

Focuses of a spherical lens

The focus of a spherical lens, also known as the main object focus, is nothing more than a point located on the main axis, where an improper image is associated. Therefore, the ray of light that emerges from the focus of a spherical lens and falls on it must be parallel to the principal axis.

According to the above, what we can conclude is that a spherical lens, whether diverging or converging, has two foci. The two foci of spherical lenses are symmetrical about the optical center of a spherical lens.

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