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The lenses are either convex or concave. They can also be a combination
of them so that one side is convex and the other concave.
The other side can also be a plane. A convex lens gathers
light while a concave lens disperses light.
A
magnifying glass is a convex lens. It gathers parallel light
beams coming from afar into one focal point.
Optics
imitates the functioning of an eye. An eye resembles camera
with a convex lens. In front of it there is the iris or a
diaphragm that regulates the aperture size. The iris regulates
the amount of light coming into the eye. A small aperture
lets only a small amount of light in, but the picture is clear.
The eyelids function as shutters. The film is replaced by
retina.
Seeing
is not continuous, instead, the eye forms individual pictures
just like a movie camera or a video camera. A person moving
at 40 km/h sees the road only at every 1 meter's distance;
that is why the visual field is hazy in the very front and
on the sides. The picture on the retina is upside-down, but
the optic nerves turn it over.
A
camera was born when it was discovered that one could place
a convex lens and a shutter over the hole of a pinhole camera,
and a chemically light-sensitive film
on the back wall. At first, film plates were used, later on,
mostly film cartridges.
A
picture is formed on the film upside-down. A lens gathers
plenty of light onto the picture. This makes it possible to
take pictures rapidly.
The
main types of lenses:
1.
Fix focus lenses:
- fixed focus - mostly no focusing
- camera has to be moved when composing different ratios
2. Zoom lenses:
- focal distance can be changed up to 16-fold or even more
Wikipedia [Optics - Wikipedia]
Khan Academy [Geometric optics | Physics library | Science | Khan Academy]
Motion Array [The Basics of Film Camera Lenses Explained - Motion Array]
Optics.org:
Photonics Resources for Scientiests and Engineers [optics.org - The Business of Photonics: Latest news, analysis and in-depth reporting]
Optics
for Kids [Home | Optics for Kids (optics4kids.org)]
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