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spherical reflector
created by
longwinter
(
thing
) by
longwinter
(1.5 mon)
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Thu Nov 16 2000 at 1:00:10
The slightly less cool thing about a spherical reflector (as opposed to a
parabolic reflector
, for example) is that it focuses to a
line
rather than a point.
This can be corrected for either by making your receiving
antenna
in the shape of a
line
, though this severely limits the range of
frequencies
you can be monitoring at any given time (
Arecibo Observatory
with its 305-m spherical dish used to have a system of several line feeds that could be swapped in and out for different observing purposes before it switched to the second correcting option...), or by implementing a series of
secondary
reflectors that can then
focus
the line signal down to a
point
.
(
thing
) by
jesler
(4.1 y)
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I like it!
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Fri Nov 16 2001 at 12:37:05
As suggested
longwinter
's writeup, a
spherical
mirror will not produce as sharp an image as a
plane mirror
will due to the lack of a definite
focal point
. However, if the mirror is small relative to its
radius of curvature
, the reflected rays will cross at very nearly a single point. This is known as the focal point and the diistance from it along the
principal axis
to the mirror is the focal length. The
focal length
is half the radius of curvature. However, this only holds if the angle of reflection is small. So,
f = r / 2
The
image
formed from a
concave
spherical mirror is always
magnified
. If the object lies between the focal point and the mirror, then the image is
virtual
(behind the mirror) and
upright
. Conversely, if the object lies beyond the focal point, the image is
real
, and
inverted
.
Although not necessarily spherical, a
spoon
is an everyday example of this
phenomenon
. When you look at the reflection of your face on the inside of a spoon, it's
upside down
. This indicates that the focal point lies between your face and the spoon. If you were to move your face closer to the spoon (and the spoon was big enough that you could still see the inside) the image would become non-inverted once your face passed the focal point.
Shaving mirror
s which magnify the image are spherical concave reflectors. However the
radius of curvature
is large enough that your face is still the right way up when you look in the mirror. If you look at a shaving mirror from several metres away, the image will be
inverted
.
printable version
chaos
parabolic reflector
retroreflective
Laser Ranging Retroreflector experiment on the Moon
Arecibo Observatory
Up on the platform of the Arecibo radio telescope
Mössbauer Effect
crocodile
Theine
antenna
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