The Bases of the Optics


Daily in our life, for example, when we look at Sparkling of a Diamond, Iridescence of Rainbow, Dazzling of Soap Bubbles and Evening Glow, we find unexpectedly various phenomena which give us a feeling of " how it's beautiful!" or " how it's mysterious!". We further find we may see our legs and hands nearer when we, ourselves, are in the bathtub or in the water. These various phenomena may be created by the light.
Let us study and think over in this column why these phenomena may be found or happened. We hope you will easily understand such things through the forgoing writings and lucid explanation of the Optics .

1. History for the discovery of the Light:.
First, we shall look at what our ancestors' thought on the light.

1-1 Ancestors' Theory on the light:

There is some writings by Euclid (around B.C.4) and Ptolemy (A.D.127~150) on
the character of going straight and reflection of the light.

In Greek period, people of Pythagorean school (Pythagoras B.C. 582~500).insisted
" what we can see the objects should be radiation of the energy from eyes to the
objects", while Democritus (B.C. 460~370) thought that " light is something of
particles jumping into eyes from the objects".
Aristotle ( B.C. 384~322) said "what we can see objects are something medium
between eyes and the objects".

Currently we understand that Democritos said " the Light is particles" and Aristotle
said "the Light is wave of medium."

1-2 New Discoveries:

(1) Refraction Law of the light:
W. Snell (Holland 1591~1626) discovered the refraction law of light through his experiments and Descartes (France 1596~1650) expressed it " The sine of the angle of incidence times the index of refraction of the first medium is equal to the sine of the angle of refraction times the index of refraction of the second medium"

(2) Discovery of Diffraction of the light:
Grimaldi (Italy 1618~1663) discovered the phenomena of diffraction of the Light and he described " when the Light hits opaque objects, it may bend and may proceed to the shadow area".

(3) Discovery of Interference of the Light:
Hooke (English 1635~1703) discovered and described that we perceive colors because of time gap when the Light comes out from the surface of the thin film such as oil film on the basis of refraction of the light back side of the film."

2. Reflection of the Light;

(1) Reflection Law of the Light:

The Incidence of the light (PO) and Reflection of the light (OQ) between the
perpendicular on the incident point(O) on the same surface are equal to on the both
angles.(i and j).

i = j

* If you have a half size of mirror against your height, you can see your whole body.

(2) Rotation of the Mirror;

In case the mirror(MM) is rotated at the angles with degrees, without changing the direction of incidence(PO), reflection is rotated in 2 times.
The rotated angle of reflection of the Light = rotated angles of the mirror surface x 2.

(3) The Reflection Ratio;

In case of the Light goes strait perpendicularly, the reflection ratio is computed as under.
This is called as Frenet' formula;

R={ ( n - 1) / ( n + 1) } 2

Frenet Formula indicates that the larger refraction ratio "n" give the the bigger the reflection ratio. Because the refraction ratio of Diamond is higher at n2.4,we can understand Diamond cut surface give the far better sparkling than glass surface
( It would be mentioned later on mysterious sparkling of Diamond.)

The incidence of the Light through the air to the Optic Glass of n=1.5 is equal to the reflection ratio of 4%. Since the surfaces of one lens are two, 8% of the light is reduced by passing through one lens. In case of zoom lens with 40 surfaces
light passing ratio become only to 20%.

We will further discuss the details of reflection later, we understand that it is not
useful unless otherwise the prevention coating on the surface of the lens is applied.

To be continued