Light Through A Lens example essay topic

Have you ever looked up to the sky at night, and wondered what stars look like up close? Have you ever wondered how astronomers take pictures of other planets with such detail? Although the human eyes are superb detectors, they cannot see extremely faint objects or fine details on distant objects. For example, you would not be able to read the print on your skateboard magazine when it is on the other side of a dimly lit room. However, if you had something that would collect more light than your eye and also increase the details that are discernible, you would be able to read the fine print in the magazine. Now, imagine that your magazine is a star far away in space.

A telescope would be the ideal instrument to better see that star. Telescopes allow observers to see faint objects in space by first gathering light, then focusing it by either reflection or refraction, and finally projecting the image to the observer. To understand how important the amount of light collected by a telescope is, it is important to understand how our eyes see an object. According to Thomas T. Arny, for our eyes to? see an object, photons (light) from the object must strike the retina? , which is a light-sensitive membrane in the back of the eye that receives the light and sends the image to the brain (Arny 120). How bright an object appears to us depends on the number of its photons that enter your eye per second.

This number is limited by the size of the eyes. Telescopes overcome this limitation by collecting photons, which are then funneled into your eye. The bigger the collecting area of a telescope, the more photons it gathers. The result of more photons is a much brighter image, which allows us to see objects that are invisible to the naked eye.

This collected light must now be focused into a smaller area to fit into the eye. There are two different ways by which this collected light is focused. The first way is called refraction, and is accomplished by passing the light through a lens. According to Terry Maloney, the lens, called an objective lens, ? focuses the light by bending the rays, which is called refraction? (Maloney 18).

This refraction occurs when light moves from one substance into a different substance, and as a result slightly changes speeds. These refracting lenses have three major problems in large telescopes. The first major problem is extremely high cost to make a large lens. A second problem is that the lens must be supported at its edges so that light can pass through, which causes the lens to sag in the middle by small amounts. The result of this sagging is distorted images. The third major problem is that when light is bent, different wavelengths (colors) are bent differently, which creates images that are fringed with color.

The second way by which light is focused overcomes these problems by using mirrors to collect and focus the light. This type of focusing is called reflection, and is used by most modern telescopes. The mirrors used in a telescope are not much different than the ones in your bathroom. According to Thomas T. Arny, the mirrors used are? made of glass that has been shaped to a smooth curve, polished, and then coated with a thin layer of aluminum or some other highly reflective material? (Arny 124). These curved mirrors can focus the light just as well as a lens, and because the light does not pass through the mirror and is not refracted, it focuses all colors equally well.

Another advantage of not passing the light through the mirror is that it can be supported from behind, which drastically reduces the sagging problems of large mirrors. The collected light is focused by the curved mirror, bounced off another mirror, and is sent into the eyepiece. It is the job of the eyepiece to allow the proper size of light beam through to the eye. According to Terry Maloney, to make full use of the light gathered by the telescope, ? the eyepiece must allow a beam of 1/3rd of an inch in diameter to enter the eye?

(Maloney 38). Any more light than this and the light grasp of the telescope is wasted; less than this and the telescope is not being used to its full capacity. An eyepiece typically consists of two lenses. The first lens, called the field lens, takes the light gathered by the objective lens and directs it into the second lens.

Then, the second lens, called the eye lens, magnifies the image and directs it into the eye. Telescopes are a very important tool for astronomers, and they are very interesting and fun to own. A telescope will allow you to see many dim objects that you may never see with your bare eye. The telescope accomplishes this by gathering more light than a human eye. Then the light is focused and passed through an eyepiece. The eyepiece adjusts the light beam to a suitable size for the eye to take in.

So, the next time you are gazing up at the stars, try using a telescope; it will open up a whole new world of interest for you. Arny, Thomas T. Explorations: An Introduction to Astronomy. New York: McGraw- Hill, 2002. Maloney, Terry. Telescopes: How to Choose and Use Them. New York: Sterling Publishing Co., 1968.