Project Update I

My original idea was to research all different kinds of lenses ranging from the human eye to telescopes. However, after doing some basic research, I realized that learning about such a large spectrum would limit how in-depth my research would be. Instead, I have decided to focus (heh) on the lens of the human eye in terms of its mechanics and how it can be adjusted (i.e., eyeglasses and contact lenses).

I will strive to answer the questions that I proposed in my first post:

• How do the lenses in our eyes change shape to maintain focus?
• What do the numbers in eye prescriptions mean?

So far, I have only been able to do some research on the basic concepts behind lenses and the lenses in a human eye:

• Lenses focus rays of light because light travels more slowly in the lens than in the air, which allows the light the "bend" and focus.

animation showing the basic idea behind lenses

• The focal point or principal focus (represented by "F") is where the light beams converge.
• The focal length (represented by "f") is the distance from the center of the lens to the focal point.

graphic showing the focal point (F) and focal length (f)

• Often, multiple lenses are used in more precise equipment such as cameras and microscopes to correct for aberrations. Aberration is a term used for when a patch of light is produced instead of a single point.
• The line that runs through the centers of these lenses is known as the principal axis.

graphic demonstrating a kind of aberration

picture of chromatic aberration

•  The human eye is able to focus through tightening/relaxing of the ciliary muscle. This muscle stretches and compresses the lens within the eye, which will bend light differently depending on the shape, which allows the eye to focus.

graphic showing how the eye focuses

The two best sources I have found so far are the Encyclopedia Britannica article on optical lenses and a page on "Accommodation" of the human eye on HyperPhysics by Georgia State University.

My questions to answer for next time are:

• What do the numbers in eye prescriptions mean? 
• Why do some of us require corrective lenses (i.e., why do we need glasses/contacts?)
• How do corrective lenses work with the human eye?