I can't believe my eyes!

The glasses, which were found by Michael in the cellar, obviously belonged to his grandfather. His grandpa has difficulties with reading and in being able to see close by objects. That's why he needs glasses. People who need classes for close by objects are called farsighted. Lenses, which have a thicker centre and thinner edges, are called converging lenses. Accordingly, Michael's grandpa is farsighted and wears glasses which are basically converging lenses.

In order to understand all of this better we should take another look at the simple model of our eye from the hint-section "A Clear Image".

An average eyeball has a diameter of about 25 millimeters. The pupil and the iris combined resemble the aperture. The retina of our eyeballs works like a screen. The images on the retina are actually upside down and reversed left to right. What we see is really something created by our brain. The retina sends its image signals along the optic nerve to the brain. There the signals are processed so that we are able to see the world right way up and left objects on the left, right objects on the right. Apart from that our eyes can also do another astonishing thing; we can focus both on close and distant objects. The lenses in our eyes are elastic which allows our eyes to focus both on distant and close by objects. With the help of the sphincter the lens can be stretched. If not stretched it remains thick and strongly curved. The different curvature determines different focal distances of our lenses - it ranges from 13 millimeters to 18 millimeters. This shape-shifting of our lens is called accommodation.
Farsightedness can have two causes. Younger people often have a too short eyeball. Older people, on the other hand, have a different problem. Accommodation no longer works for them which means that the focal distance of the lens can no longer be adjusted as needed. If that is the case we call that presbyopia. In both cases a clear image is produced behind the retina and the person can see close by objects only very blurred.
To correct farsightedness converging lenses are used. Light is thus converged more strongly. This additional light refraction the focal distance is shortened; the clear image is produced further to the front, on the retina.

In the first image you can see what happens to light in a farsighted eyeball. As you can see the clear image is produced behind the retina. In the second image a converging lens has been added in front of the eyeball. The light rays are getting converged. The clear image is then produced on the retina and the visual disorder is successfully compensated.