Missing figures
PROPERTIES OF LENSES, OPTICAL GLASS
Composition
Glass is a solid, structureless and amorphous. There are two main group classification of optical glass:
1. Crown, and
2. Flint (has a high content of lead oxide)
Chemicals are combined to produce new glass types. These new glass types are used to benefit other different types of cameras (such as high-speed minature cameras, black/white cameras, etc).
Properties
The most important optical characteristics of a glass are its refractive index and its degree of dispersion.
Refraction is the phenomenon of a light ray that passes from air to glass or from glass to air, and is deflected from its path when it meets the glass surface at an angle. The glasses magnitude depends on two things: the material of the glass and its wavelength. We can see wavelengths as coloured light from (spectrum colours) red, orange, yellow, green, blue, indigo and violet. An example of this is the refraction of light on a raindrop, where we may see a rainbow.
Note, that the shorter the wavelength of the light, the more the ray strikes the glass surface is refracted. Blue and violet rays are deflected more than red rays. The degree of the deflection is a case characterized by a value, the refractive index n. It varies from the different colours of the spectrum. The degree of refraction is given by Snellius's law of refraction:
where r is the angle or refraction and i is the angle of incidence
The value of n for air is 1.00, water is 1.33, crown glass is 1.46 to 1.72 and flint glass is 1.55 to 1.80.
In a camera, light is transmitted by the aperture. It forms on the screen a circle of light which is the image of the object point. When the distance of the screen from the aperture is increased, the image will become larger as well as the diameter of the circle of light (image point). The size of the aperature depends on the diameter of the circle of light from the image. The light that passes the aperature is scattered or diffracted. So, if the aperature is too small, the image may become less sharp because of the scatter of light at the aperature opening. A sharp image must have a aperture large enough to reduce the effects of diffraction to a minimum.
Lens Shapes
A lens is a glass body bounded by two surfaces centred on the optical axis of the lens.
For an eye to focus correctly on an object, it must be placed in a certain position in front of the eye. The primary focal point is the point along the optical axis where an object can be placed for parallel rays to come from the lens. The secondary focal point is the point along the optical axis where in coming parallel rays are brought into focus. The primary focal point has the object's image at infinity, where as the secondary focal point has the object at infinity. For people who have myopic eyes, the secondary focal point is anterior to the retina in the vitreous. Thus, the object must be moved forward from infinity, in order to be focused on the retina. The far point is determined by the object's distance where light rays focus on the retina while the eye is not accommodating. The far point in the myopic eye is between the cornea and infinity. The near point is determined by which an object will be in focus on the retina when the eye is accommodating. Thus, moving an object closer will cause the perception of the object to blur. The measurement of these refractive errors are in standard units called diopters (D). A diopter is the reciprocal of a distance of the far point in meters (Vander & Gault, 1998). The myopic condition manipulates these variables in order to ultimately make a nearsighted individual.
...te evidence as to how it would be a solid or even how it would occur to be one. It seems that this debate is evenly divided between specialists. Even more interesting is that most of the chemists and material specialists seem to believe that glass is clearly an amorphous solid and have scientific facts such as the structure of amorphous solids that has long been defined. On the other side, we see more physicists concluding that glass is either not a defined state yet or is a “super-cooled” liquid moving at a rate too slow to be defined. The solution to the glass transition has many more years of research to go and does not seem to be coming to a conclusion anytime soon. Glass may even possibly be its very own state outside of the common four states of matter. In the words of Dr. Harrowell, “Glass is an example, probably the simplest example, of the truly complex”.
The crystalline lens is a fibrous, jelly-like material that serves to fine tune the vision process by adjusting its shape and therefore the focal length of the system.
Refraction occurs when light travels from one medium crosses a boundary and enters another medium of different properties. For example, light traveling from air to water. The amount of refraction (or bending) can be calculated using Snell's Law.
“The camera may be thought of as a comparable to the eye. The difference is
When light comes in contact with the surface, it can be absorbed, reflected, transmitted or refracted. Type of light that is reflected from the surface determines our perception of color that surface in. Colorimeters and spectrophotometers is affected by absorption and transmission of light to measure the
The air in between the layers of glass should be thick and dense, so that it can save energy. One of the most common airs used in-between glass is argon. When argon is used heat loss is reduced. You could also use carbon dioxide or sulfur hexa-fluoride between glass.
There is evidence of glass making from as early as 4000 BC. Back then it was mostly used for the coating of stone beads. It was 1500 BC when the first hollow glass container was made. It was made by covering a sand core with a layer of molten glass. It was during the First Century BC that glass blowing became more common. At this time glass was high coloured due to the impurities of the raw materials that were used to make it. The first recorded colourless glass was made in First Century AD. The Romans were one of the most skilled in glass making and held most of the secrets. It wasn’t until the Roman Empire began to fall that the secrets began to leak out into Europe and the Middle East. At this time the greatest reputation for technical skill and artistic ability was held by the Venetians. A far amount of Venetian craftsmen left Italy to set up their own glassworks.
Newton acquired many of these lenses and began to experiment with how they could manipulate rays of light. In one of his experiments he had a beam of sunlight pass through one of the prisms and observed a spectrum of light hitting the wall of a dark room. He continues to manipulate these experiments. In one he drilled a small hole into a board placed against a window and then placed a prism over the hole. He projected this beam of light onto a wall as well as on a white sheet of paper. This created a round white image with a sliver of blue around the upper rim and red around the lower rim. He performed another experiment in which he had a beam of white light pass through one prism which separated the different colors and then made it pass through an identical prism that was upside down, which turned the beam back into plain white light. Through these experiments he showed that light can be both decomposed and put back
Perhaps the greatest contribution to the astronomy was the intervention of the reflecting telescope. Further, he analyzed the properties of glass and came to the conclusion that refracting telescopes would always suffer from the noticeable aberrations. Further, the fundamental problem was the chromatic aberration. It arises from the prism-like effect, as light passes through a lens and is bent. Besides, every wavelength of the light is bent by the different amount. In essence, the red light appears to be bent more than the blue
The refractive index of lens is larger than air therefore refraction in lenses occurs differently. It happens when light moves parallel to the normal and is refracted through the focal point. If a ray passes through the optical center of the lens, the ray would continue without being refracted. The optical direction is the point on the normal where the incident direction of a ray is parallel to the emergent direction.
Refraction of Light Aim: To find a relationship between the angles of incidence and the angles of refraction by obtaining a set of readings for the angles of incidence and refraction as a light ray passes from air into perspex. Introduction: Refraction is the bending of a wave when it enters a medium where it's speed is different. The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the normal to the boundary between the two media. The amount of bending depends on the indices of refraction of the two media and is described quantitatively by Snell's Law. (Refer to diagram below)
Now in order to understand how lights is able to be refracted in different angles, it is important to understand the Snell’s Law which states that, the refractive angle always depend on the refractive index of both media. Now, the refractive index keeps on changing depending on the wavelength of the light passing through. Light, as we know, it is a wave that has different wavelength. Each wavelength represents a different color. Thus, different colors will have different refractive index when passed through the same media. It is important to note that light is normally refracted twice when it travels through a prism, first on its way in, and when it is going back.
When a ray of light is bounced or reflected off of a plane surface, there is a specific law that can be used to predict the angle at which it is reflected off of the surface. This is known as the ‘Law of Reflection’ and it states: