REFRACTION

1. REFRACTION

2. CAMERA A Bit of History Cameras have changed a lot in the past 400 years. “Camera” means “chamber”, and in fact the first cameras really were chambers. Artists used the camera obscura, or pinhole camera, to project an upside-down image of a brightly-lit scene onto a canvas. The artist could then trace the outlines of the scene. The next step is to remove the artist. Was there a way to make the image permanent? If you’ve read about photographic film, then you know about the first efforts to permanently record images made by light. Inventors such as Joseph Niépce, Jacques Daguerre, and William Fox Talbot all made advances in recording images, and each of these advances changed the form and function of the camera.

3. Cameras really started to change the world with the introduction of the “Brownie” camera in 1900. With the Brownie, photography was no longer just for professional photographers; the average family could now own a camera. Snapshots, spontaneous, and un-posed images started to record everyday life. This miniature camera was inexpensive and easy to use, and versions of the Brownie were still being sold into the 1960s. Digital cameras are beginning to change photography at least as much as the Brownie did over a hundred years ago. With digital photography, not only can pictures be taken at will, but they can be downloaded to a computer and sent all over the world with just a few clicks of the mouse.

4. How It Works Every camera is essentially a lightproof box, with some method of letting in just a small amount of light at just the right time. Once the light is in the box, it forms an image (like in the camera obscura), causes a chemical reaction on photographic film (like in the Brownie camera), or energizes a photocell (like in a digital camera). To find out how the light gets in to do its thing, let’s imagine what happens when you snap a picture, maybe of a dolphin playing in the surf. (You can see right away that a camera obscura wouldn’t do you much good for this kind of picture!) When you press the button on an SLR camera, the mirror flips up exposing the film to the light coming through the lens.

5. One kind of camera — which can be either a digital camera or a traditional film camera — is called a single-lens reflex (SLR) camera. In this camera, there is only a single set of lenses for both viewing and photographing an image. Let’s say you spot your dolphin and lift your camera to your eye. What happens? • First, light bouncing off the dolphin passes into the camera, through a set of lenses, and onto a mirror. From there, the light bounces up and into a funny-shaped piece of glass called a pentaprism (penta means five, and the pentaprism has, you guessed it, five sides). Once light enters the pentaprism, it bounces around in a complicated way until it passes through the eyepiece and enters your eye. • The dolphin is swimming just below the water, but you have a feeling it’s about to surface. Wait for it, wait for it…there! You snap the picture. When you press the button on the camera, the mirror flips up out of the way. Instead of bouncing into the pentaprism, light from the dolphin passes directly to the back of the camera. There, it either hits photographic film and starts a chemical reaction, or else it impacts an array of light-sensitive cells that release a tiny electric charge in each activated cell. Either way, even though the dolphin’s long gone, you’ve captured its image. Congratulations! • SLRs are not the only camera type. Many of us use direct vision compact cameras or just “compacts”. In this camera, the lens for viewing is separate from the lens we use to take photographs. Because of the two sets of lenses, compacts don’t need a pentaprism or a hinged mirror, making them smaller and lighter than the SLRs.

6. TELESCOPE A page from one of Galileo's notebooks showing notes about Jupiter and its moons. A Bit of History Galileo Galilei didn’t invent the telescope. Even so, it was when the great Italian scientist pointed a telescope toward the night (and even the day) sky that the world changed forever.Galileo discovered the planet Venus has phases, just like the Moon. No one could have known that until the telescope was invented. Galileo saw that the Moon had craters and mountains, and that the Sun had moving black spots on its face. He also discovered four new moons circling the planet Jupiter. All these discoveries helped show that the Earth is not the centre of the universe, that the planets orbit a changing and imperfect Sun, and that the planets are other worlds, something like the Earth but very far away. With his telescope, Galileo literally remade the world. Galileo’s telescope was a refracting telescope. Isaac Newton, who was born the same day Galileo died, invented another kind of telescope, called a reflecting telescope. Reflecting telescopes use mirrors instead of lenses to make faraway things look bigger. Reflecting telescopes can be made much more powerful than refractors, and Newton’s invention paved the way for all the great telescopes to come.

7. Refracting telescopes depend on one amazing fact. As light passes through glass, it slows down. Slowing down a light beam makes it bend. Why? Imagine you’re pulling a wagon along a sidewalk, when the wheels on one side slip off into the grass. The wheels turn slower in the grass than they do on the sidewalk, and the wagon moves toward the grass. In the same way, when a light beam passes through a glass lens inside a telescope, it moves toward the lens. When the light beam comes out the other side, it’s bent! The shape of the lens means light near the top of the lens is bent down and light near the bottom of the lens is bent up. Somewhere inside the tube the light beams cross, but before they can spread out again the eyepiece lens bends the light beams again and sends them to the eye.

8. Because the light beams cross, the image ends up upside-down. This doesn’t matter much when you’re looking at Mars or the Moon (remember there’s no real up or down in space), but refracting telescopes used to see objects here on Earth often have another set of lenses to flip the image right-side up again Refracting telescopes are simpler than reflecting telescopes, but they have an important limitation. Remember that the light passing through the glass lens gets bent. It turns out that different colours are bent different amounts, and that causes the light to become unfocused. Isaac Newton solved this problem by replacing the lenses with mirrors. When light hits a mirror, it doesn’t bend. Instead, it bounces off. Just like a ball bouncing off a wall, a light beam comes off a mirror the same way it comes in. In other words, the angle in equals the angle out. And that rule is true for all the light, no matter its colour. The primary mirror in a reflecting telescope is curved just the right amount to bounce all the light onto the secondary mirror. From there, the light passes through the eyepiece lens, which bends the light into the eye.

9. MICROSCOPE A Bit of History Just as Galileo didn’t invent the telescope, Anton van Leeuwenhoek didn’t invent the microscope. Yet, just as Galileo discovered an unknown universe of the very large when he pointed his telescope upward, Leeuwenhoek discovered an unknown universe of the very small when he used the microscope to look where no one had before. Leeuwenhoek examined the microscopic world, discovering tiny animals, plants, and bacteria in a drop of water. He studied blood cells and how they move, even exploring the life cycles of insects. Because of his pioneering work, Leeuwenhoek is often called “the father of microscopy”.

10. How It Works A microscope uses the same trick as a refracting telescope — light waves being bent as they travel through glass. In a telescope, the idea is to bend parallel light from very faraway objects into a small focus at the eye. In a microscope, the idea is to bend diverging (spreading-out) light into a parallel path, then bend that parallel-path light into a small focus at the eye. To make a little more sense of that, let’s try to magnify something. Maybe it’s a dust mite, a tiny bug that lives in your pillow and eats your dead skin (ew!). First, we have to light up the dust mite. A mirror mounted under the microscope stand does the job. Light bounces off the mirror, passes through and around our dust mite (mounted firmly to a microscope slide), and into the objective lenses. These lenses bend some of the spread-out light beams from the dust mite into straight line paths that travel through the microscope tube. Next, the light beams reach the eyepiece lenses. These lenses bend the light back into your eye, so you can see the dust mite up close and personal. The power of the microscope depends on how much each lens bends the light. Usually, the power is written right on the microscope itself. 40x, for instance, means that the image at the eyepiece is 40 times larger than real life.

11. MAGNIFY LENS How Does a Magnifying Lens Work? Convex Lens A magnifying glass is a convex lens. A convex lens is a type of spherical lens. That means that the magnifying glass consists of two sides of glass and that it is thicker in the middle than the outer edges. The thickness is because the glass bows outward in the middle. The shape of the glass distorts the way we see the image on the other side. What You're Looking At When you look through a magnifying glass at an object, you are focusing on one central point of interest. The object under the center of the magnifying glass appears larger. Objects toward the outside edge of the magnifying glass appear normal size or smaller.

12. Focal Length If you put the magnifying glass too far from an object it will appear smaller. The magnifying glass must be placed closer to the object than the distance of the focal length of the glass. Magnification The amount of magnification of an object refers to how many times larger it appears than it actually is. This is usually expressed by saying 2x magnification. The 2x is the power of magnification. When using a magnifying glass, you control some of that power by how far away your eye is from the magnifying glass. Light The way a magnifying glass works is by bending light. As light passes through a convex lens, it is bent by the glass. Our eyes perceive the bent light as a bigger object, even though the object itself has not changed in size at all.

13. Projector What Is a Projector? A projector is any device which creates a light-projected image by shining a light through a small, transparent image. In order to refine this image, projectors must also employ lenses in order to focus the light. Projectors can transform a very small image into a large one because the image which is projected will be the same size as the pool of light created by the light source behind the transparent image. There are many different kinds of projectors, but they work on the same basic principle. One of the more complicated of the commonly known projectors is the movie projector.

14. Movie Projectors • The modern movie projector evolved out of the slide projector. A slide projector focuses, projects and enlarges an image which is made from a photograph. In order to be projected, these images have to be rendered in a transparent format onto various forms of clear plastic, such as nitrocelluloid. The slide projector moves these individual images into a precise location in front of the projector light and behind the lens(es).A movie projector works on a similar principle, but in this case, the individual photos are strung together on one extremely long piece of film. This film is wound around a spool and the projector contains a motorized unit which winds the film from one spool to another. In between spools, the film is stretched between the light and lenses and projected onto a large, white screen. The screen is white in order to provide the images with an opaque quality, just as photographs are printed on white paper. Visual Perception • No form of moving image projection or animation really utilizes true moving images. Instead, single, non-moving photos or illustrations depict objects or people in various progressive, chronological states of movement. As the human eye processes visual data, each image entering the brain is retained for a brief period of time. This phenomenon is referred to in the theory of "persistence of vision." As a film projector moves through a reel of film, it pauses for a tiny fraction of a second at each image, but this amount of time is actually less than the amount of time that it takes for the human brain to move from one image to the next. This means that the eye and brain can't distinguish between the visual data of actual moving objects and the visual data of the still film images, so the images appear to be moving.

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