Application of Light Waves – Everything You Need To Know
In this article, we shall discuss the change in the application of light waves and the application of the properties of lenses.
At the end of the article, the reader should be able to:
- Construct a model of a box camera.
- Explain the optical principles involved in the snapshot camera.
- Set up a single lens project and use it to project a film strip on a screen.
- Explain the formation of images by the camera and the projector by tracing rays of light through them.
- Explain the role played by some parts of the eye in the formation of the image on the retina.
- Compare and contrast the eye and the camera.
- State the defects of the eye and their causes.
- Identify the type of lenses for correcting the various defects of the eye.
- Trace the paths of light rays through simple and compound microscopes and telescopes.
The Simple Camera and Projector
The Simple Lens Camera
The simple lens camera consists of a light-proof box with a converging lens in the front and a light-sensitive film at the back. The function of the lens is to focus images of the object to be photographed onto the light-sensitive plate or film. There is a provision for adjusting the distance between the lens and the film so that objects in front of the lens can always be sharply focused on the film.
Sometimes the convex lens is replaced by a system of lenses. The simple lens camera has a fixed distance between the lens and the film. This distance is equal to the focal length of the lens.
Some cameras have bellows or focusing rings by which the distance between the lens and the film can be adjusted.
The diaphram and the shutter control the amount of light entering the camera. The diaphram regulates the size of an aperture or opening which controls the amount of light energy sensitizing the film. The shutter, of variable speed, between the lens and the film controls the time interval during which light is allowed to fall on the film. This time interval is called the exposure time.
The process of making a photograph begins and ends with light. Rays of light enter a camera and are focused on an image. The light exposes the film in the camera causing chemical changes on the film’s surface. The exposed film is then treated with certain chemicals in a procedure called developing. Finally, light is used to make a print by transferring the image from the film to a sheet of special paper.
To take a photograph, the camera lens is pointed at the object and the focusing ring is used to adjust the distance of the lens from the film until a sharp image is seen on the film. When the button is pressed, the shutter quickly opens and closes, exposing the film, for a brief period, to light from the object. After the photograph is taken the film is wound between two spools until it is all used up.
The projector is an instrument for projecting on a screen an enlarged image of a transparent object, for example, a slide. Fig. 14.3 shows the essential parts of a projector and its optical arrangements.
The functions of the various parts of the projector are:
- The small but powerful light source illuminates the object which is usually non-luminous. A converging mirror placed behind the light source helps to direct the light onto the film or slide.
- The condenser consisting of two plano-convex lenses collects the light from the light source and concentrates it on the slide or transparency and illuminates every part of it strongly and evenly. Between the two lenses is usually an infra-red filter to prevent the passage of heat to the slide which might otherwise melt it.
- The slide carrier is a framework in which the slide is placed upside down so that it will appear erect on the screen.
- The projection lens placed near the slide produces a real enlarged and inverted image of the slide and focuses it on the screen. The lens is at a distance of between f and 2f from the object, where f is the focal length of the lens.
- The screen, usually white, receives the image which is the right way up if the object is inserted upside down into the slide carrier.
The principle of the slide projector is used in cine-projectors, photographic enlargers, and several other devices.
You can also read the Sources of Light, Transmission, and Reflection of Light.