Download 6.2 Extending Human Vision Microscopes • A compound light

6.2 Extending Human Vision
Microscopes
•  A compound light microscope
uses two convex lenses to
magnify small, close objects.
w  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.
w  Adjusting the distance to make the
image clear is called focussing.
See pages 216 - 217
(c) McGraw Hill Ryerson 2007
Refracting Telescopes
•  A refracting telescope has a
convex lens to collect and
focus light from a distant
object, and a convex eyepiece
lens to magnify the image.
•  Problems with refracting
telescopes include:
w  Large objective lenses flex, due
to their own weight and distort
the image.
w  Glass lenses, even of the highest
quality, absorbs some of the light
and are expensive.
See page 219
(c) McGraw Hill Ryerson 2007
Reflecting Telescopes
•  A reflecting telescope uses a
concave mirror, a plane mirror,
and a convex lens.
w  Light enters the telescope and is
focused after reflecting off the
concave mirror.
w  A plane mirror reflects the light
towards the eyepiece.
w  The convex lens in the eyepiece
magnifies the image.
•  Most large telescopes are
reflecting telescopes.
See page 220
(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.
See page 221
(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.
•  Cameras can have different types of
lenses.
w  Wide-angle lens allow for a wide field of
view.
w  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
Eye
Eyelid
Iris
Retina
Rods and cones
Camera
Lens cap
Diaphragm
Charge-coupled device(CCD)
pixels
See page 223
(c) McGraw Hill Ryerson 2007
The Pinhole Camera
•  Other than by a lens or a spherical mirror, an image can
also be produced by a small hole. This is often referred
to as a pinhole camera.
•  Generally the smaller the hole the better (sharper) the
image, but the brightness of the image also decreases
with a smaller aperture (hole).
•  This is a good way to
observe the image of
the sun safely during a
solar eclipse.
pinhole
(c) McGraw Hill Ryerson 2007
Lasers and Laser Surgery
•  Laser light is light of only one
wavelength.
•  Can travel great distances
without spreading out and
contains a lot of energy.
•  Lasers can be used in place
of scalpels in surgery.
w  Remove cataracts
w  Reattach retina
w  Laser eye surgery to reshape
the cornea.
Laser surgery
See page 224
(c) McGraw Hill Ryerson 2007
Optical Fibres
•  Optical fibres are transparent glass
fibres that can transmit light from
one place to another.
•  Optical fibres transmit light using
total internal reflection.
Optical fibre
w  Total internal reflection is when light
strikes a boundary between two
materials and is totally reflected.
•  Optical fibres are used for:
w  Medical procedures (orthoscopic
surgery)
w  Telecommunications (telephone,
internet, video)
See page 225
Take the Section 6.2 Quiz
(c) McGraw Hill Ryerson 2007