Lens Applications- 13.5                                              James Kovacs and Jack Learoyd

 So far we have learnt about what a lens is and how it affects light rays when they pass through it; however, we do not know why or how lenses are used, we live in a world of lenses. Lenses are used in many everyday objects such as glasses, cameras and even your own eyes as well as some objects not seen so commonly outside of a classroom or movie theatre such as telescopes, microscopes, and projectors.

To learn more about lenses visit: http://science.howstuffworks.com/lens-info.htm

Cameras 

Lenses are used in cameras to magnify the object that is being photographed. Camera lenses achieve this by how much they are curved(how far out the centre of the lens is). The more bent the lens is the more acute the bending angle becomes. If the bending angle is acute the light rays will make a sharper bend, converging closer to the lens. Consequently a flatter lens will allow the light rays to converge farther away from the lens, if a lens is rounder it will produce a smaller image. If the distance between the real image and the lens is increased the real image will get bigger because the light rays spread out more.
To learn more about Cameras visit: http://electronics.howstuffworks.com/camera2.htm

Movie Projector
The projector is the opposite of a camera because it takes a small object(the film) and projects it on to a big object(the screen) because of this film needs to be placed between F' and 2F'. Since the lens used in a projector creates an inverted image the film needs to be
loaded in upside down so that the image on the screen is seen upright. Projectors create an upright, inverted, real image.
To see how a Projector works visit: http://entertainment.howstuffworks.com/movie-projector.htm

Magnifying Glass

Lenses are also used in magnifying glasses. A magnifying glass is probably the most simple use for a lens as it is basically a converging lens attached to a handle. As you would expect, a magnifying glass behaves exactly like a converging lens. When the object you are trying observe is placed on the opposite side of the lens in comparison to your eyes the result will be you seeing a larger, upright, virtual image. This can be extremely helpful for people with bad eyesight who needs to read fine print, a diagram can be seen below on how a magnifying glass produces a larger image. Another place you can see magnifying glasses are at camp fires. This is because it concentrates light rays from the sun creating high temperatures which if concentrated on a dry leaf or piece of wood will create a fire. Here is a good video on how a magnifying glass works. The terminology is a bit more advanced than what we have learned but it still describes how a magnifying glass and lenses in general work.

To see how Magnifying glass works watch: http://m.youtube.com/watch?v=3jR-rm1vJAE&desktop_uri=%2Fwatch%3Fv%3D3jR-rm1vJAE

To learn more about Magnifying glass visit: http://www.ehow.com/how-does_4567139_magnifying-glasses-work.html

The Compound Microscope

The Compound Microscope is made up of two converging lenses and it produces two enlarged, inverted images. One of these images are real and one is virtual. The real image that is formed is produced by the objective lens and is not seen because it is in the body tube of the microscope. The body tube is located between the objective and the eye piece lenses. The virtual image is created by the eyepiece lens, this image is the larger image that you do see.
To learn more about compound microscopes visit: http://www.youtube.com/watch?v=09nBsidXs0g

The Refracting Telescope
The Refracting Telescope is a shares some characteristics with the compound microscope. The difference is that the object is much farther away. The object is so far beyond 2F' that incident rays passing through the objective lens are considered parallel. This telescope produces two enlarged and inverted images. Like the compound microscope one image is real which is not seen (inside tube of the telescope) and one larger virtual image that is seen. Unfortunately because of gravity there is a size limit on refracting telescopes. If the objective lens is to large, it will begin to slightly droop under its own weight which will create distorted images. The largest refractor in the world has a diameter of 1.02 m and is called the Yerkes telescope. Images created with refracting telescopes are inverted, this is not a problem when viewing distant stellar objects. However this cal be a problem if you are viewing images on earth. If you wish to view images on Earth you will need a terrestrial telescope which has a third converging lens between the objective lens and the eye piece. This extra lens corrects the inverted image and allows you to always see the upright image.
To learn more about telescopes visit: http://science.howstuffworks.com/telescope1.htm
To learn more about the Yerkes telescope visit: http://amazing-space.stsci.edu/resources/explorations/groundup/lesson/scopes/yerkes/