EXTENDING HUMAN VISION

Extending Human Vision With light, mirrors, and lenses, we have been able to make microscopes and telescopes Microscopes and telescopes have allowed us to see and learn new things (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 Microscopes A compound light microscope uses two convex lenses to magnify small, close objects. Magnify means to make the image look larger than the real size. To focus the image, the object is moved closer to or farther away from the object lens. Adjusting the distance to make the image clear is called focusing. light reflects off the mirror, through the object, though the objective lens and eyepiece lens, into the eye See pages 216 - 217 (c) McGraw Hill Ryerson 2007

the objective lens has a fixed focal point if an object is between 1-2 focal lengths away from the lens, the image is enlarged the eyepiece lens magnifies the image (10X), and the objective lens magnifies it again (usually 4X, 10X, 40X)

Telescopes Help us see objects that are too far away to be seen clearly with the naked eye. Far away objects appear dim because less light enters your eye. Two main types of telescopes: Refracting and Reflecting Telescopes

Refracting Telescope

Refracting Telescopes uses two lenses: a convex objective lens to collect and focus light from a distant object, a convex eyepiece lens to magnify the image. It needs very large lenses! Sometimes, they are too big: Heavy Distort image Expensive Difficult to make See page 219 (c) McGraw Hill Ryerson 2007

Problems with Refracting Telescopes Large objective lenses tend to flex, due to their own weight which can distort the image. Glass lenses, even of the highest quality, absorb some of the light and are expensive. It needs very large lenses! Sometimes, they are too big: Heavy Distort image Expensive Difficult to make See page 219 (c) McGraw Hill Ryerson 2007

Reflecting Telescopes TWO mirrors (plane and concave) and a convex lens: Light enters the telescope and is reflected off a concave mirror at the bottom. A plane mirror reflects the light towards the eyepiece A convex lens in the eyepiece magnifies the image. Most large telescopes, like those used in space, are reflecting telescopes. the light reflects off the concave mirror and strikes a plane mirror at an angle before it converges to its focal point the light reflects into the eyepiece, which is a convex lens that magnifies object some telescopes collect light rays using several mirrors and then combine the rays into a single image (e.g. The Keck Telescope) See page 220 (c) McGraw Hill Ryerson 2007

The Hubble Space Telescope – is a Reflecting Earth’s atmosphere blurs the image of distant objects in space, just like water blurs your vision to overcome this blurry effect, some telescopes are placed in space The Hubble Space Telescope was launched into outer space in 1990- it is a reflecting telescope that uses two mirrors.

(c) McGraw Hill Ryerson 2007 Binoculars Binoculars are actually two refracting telescopes mounted side by side. To shorten the length of the tubes in binoculars, prisms are used to reflect the light back and forth. thumbscrews on binoculars are used to change the focal length in order to focus on the object being viewed See page 221 (c) McGraw Hill Ryerson 2007

Cameras

(c) McGraw Hill Ryerson 2007 Cameras Light enters the camera through an opening called the aperture. Light then passes through a lens which focuses the image on the light detector. A telephoto lens See page 222 (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 Camera Lenses Wide-angle lens allow for a wide field of view. Telephoto lenses allow distant object to appear larger. A telephoto lens See page 222 (c) McGraw Hill Ryerson 2007

Cameras Have Similarities to Human Eyes Eyelid Iris Retina Rods and cones Camera Lens cap Diaphragm Charge-coupled device(CCD) pixels See page 223 (c) McGraw Hill Ryerson 2007

How to Bring an Image into Focus to focus properly, the screen that is receiving the image must be the correct distance from the lens (where the light rays converge) if the screen is too close or too far from the lens, the image will appear blurry this is similar to near-sightedness and far-sightedness

Lasers only one wavelength all of the light rays move in the same direction, laser light can travel great distances without spreading out and can contain a lot of energy. and the crests and troughs line up.

Because laser light contains only one wavelength- it does not make a rainbow

Lasers and Laser Surgery Lasers can be used in surgery in place of scalpels. Remove cataracts Reattach retinas Laser eye surgery to reshape the cornea. stop bleeding Laser surgery See page 224 (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 Eye surgery video Animation: https://www.youtube.com/watch?v=Xsg07RqvGFE Real: https://www.youtube.com/watch?v=TBfAuvOPjeg (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 Optical Fibres Optical fibres are transparent glass fibres that can transmit light from one place to another using total internal reflection. Total internal reflection is when light strikes a boundary between two materials and is totally reflected. Optical fibre See page 225 (c) McGraw Hill Ryerson 2007 Take the Section 6.2 Quiz

Optical Fibres are used for Medical procedures (orthoscopic surgery) Telecommunications (telephone, internet, video) Optical fibre (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 Homework Complete WS Read Eye Dissection in text p 212 Watch Eye Dissection Video: https://www.youtube.com/watch?v=0rbCrJoTatE (c) McGraw Hill Ryerson 2007