Detecting, collecting & focusing light
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DETECTING, COLLECTING &
FOCUSING LIGHT
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TelescopeThe main purpose of a telescope is to capture
more light and see fainter objects than our
eyes allow us to see.
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Telescopes come in many different varieties but
they all boils down into two major principles.
Refracting and Reflecting of light.
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Refracting TelescopeA refracting telescope uses a convex mirror
(the center is thicker than the edges) to focus light.
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The refraction properties of glass (the way it bends light) are used to gather parallel rays of light and
focus them to a point. The image is created at the
focal point of the telescope.
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Reflecting telescopeA reflecting telescope uses a concave mirror
instead of convex mirror to collect and focus light.
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A large concave mirror (the center is thinner
than the edges) collects and reflects the light to
make an image.
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Reflecting telescopes can see objects that are a
millionth or a billionth the brightness of the faintest
star that can be seen by the human eye alone.
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Objective/Primary Mirror
The large, concave, light-gathering mirror in a reflecting telescope.
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Diagonal/Secondary Mirror
In a reflecting telescope, a mirror that directs the light from the primary
mirror to a focal position.
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Cassegrain TelescopeA type of reflecting telescope in which
incoming light hits the primary mirror and is then
reflected upward toward the prime focus,
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where a secondary mirror reflects the light back down through a small hole in the main mirror into a detector
or eyepiece.
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Newtonian TelescopeA reflecting telescope designed
so that the focused light is reflected by a small secondary
mirror out to the side of the telescope, where it can be
viewed.
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ApertureThe opening in a telescope or other optical instrument that determines how much
light it collects.
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The size of the diaphragm opening in a telescope’s lens
regulates amount of light passes through onto the film
inside the camera the moment when the shutter curtain in telescope opens during an
exposure process.
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LensAn optical instrument, made
of glass or some other transparent material, shaped so that parallel rays of light
passing through it are bent to arrive at a single focus.
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FilterColor filters are usually
constructed using transparent pieces of dyed glass, plastic,
lacquered gelatin (e.g. Wratten filters) that have been treated to selectively transmit the desired wavelengths while restricting
others
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The two most common types of
filters in use today
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Absorption FiltersAbsorb unwanted
wavelengths.They are used to create special
effects in a number of photography applications and
are widely employed in the cinema industry.
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In addition, absorption filters are commonly found in signs and traffic signals and as directional signals
on automobiles, boats, and airplanes.
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Interference FiltersRemove selected
wavelengths by internal destructive interference
and reflection.
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These filters differ from absorption filters in the fact that they reflect and
destructively interfere with unwanted wavelengths as
opposed to absorbing them.
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CCDCharged-coupled device:
an electronic device that records the intensity of light falling on it. Have replaced film in most astronomical
applications.
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When you take a picture with a digital camera, the
image is recorded by a sensor, called a "charged coupled device" or CCD
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Focal PlaneThe surface where the
lenses and/or mirrors of a telescope form an image of
a distant object.
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FocusAlso called an image
point, a point in an optical system in which light rays are brought together; the location where an image forms in such systems.
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CoherentA relationship indicating
that electromagnetic waves are in synchronization with each other. Waves that are coherent exhibit persistent
interference effects.
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Chromatic AberrationA distortion of an
optical system that results in different colors not
focusing in the same way, often producing color
fringes or distorted shapes.
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DispersionThe spreading of light
or other electromagnetic radiation into a spectrum. A rainbow is an example of
the dispersion of light caused by raindrops.
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False-color imageA depiction of an
astronomical object in which the colors are not the object's real colors.
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Instead, they are colors arbitrarily chosen to
represent other properties of the body, such as the intensity of radiation at other than visible wave
lengths.
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Photoelectric EffectEmission of electrons
from a material when light of a high-enough frequency
strikes it.
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Regardless of the brightness of the light, no
electrons are emitted unless the photons' energy is greater than a value that depends on the material.
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PixelThe term "pixel" is
actually short for "Picture Element." These small
little dots are what make up the images on computer
displays.
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The screen is divided up into a matrix of thousands or even millions of pixels. Typically, you cannot see
the individual pixels, because they are so small.
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Surface BrightnessThe overall brightness
of an extended astronomical
object such as a galaxy, star cluster, or nebula.
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Ex: a galaxy with a high density of stars will have a
high surface brightness, but one with the same number of stars more
widely spread out will have a lower surface brightness.
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THE END!
THANK YOU!!!