FREQUENTLY ASKED QUESTIONS
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- Can you suggest any good books on holography?
My favorite is "Practical Holography", by Graham Saxby, published by
Prentice Hall,
London. The "Holography Handbook"by Fred Unterseher, published by Ross
Books, Berkeley,
CA, is a good beginner's guide.
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Is the right word Hologram or
Holograph?
The preferred word is Hologram. The dictionary
defines
a Holograph as a hand written document, as in a holographic will or
deed. A
Holographer is someone who makes holograms.
Holography
is the word for the technology and artform. According to Isaac
Asimov, a Holographist is a person who collects or
studies
holography but does not make holograms. Things pertaining to holography
are
said to be Holographic.
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Are holograms projections?
No, holograms are not projected. There is no projector. It is
simply a piece of film.
Light fills up a hologram like
plaster would fill up a cast. Technically, they are reconstructions
of the light that reflected off the object.
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If a hologram breaks is the whole image visible in each
piece?
No, each broken piece would let you see the image from its own
unique
perspective. Think of a hologram as a window. Anywhere you look
through a
window you see what's on the other side. If you were to paint the
window black
and scratch a hole in the paint on the left side of that window just big
enough
to look through, you would see everything on the other side of the
window. Like
looking through a peephole. If you then scratch another viewing peephole
somewhere
on the right side of the window, you still can see through, but from a
different
perspective. This is the same effect that each broken piece of a
hologram would
display. Just remember that if you have two broken pieces taken from
opposite
sides of the hologram, and you are looking at an object that looks
differently
from each side, one piece may let you see just one of those sides while
the
other piece will let you view the other side. So, you might say that
each piece
of a hologram stores information about the whole image, but from its own
viewing
angle. No two pieces will give you a view that is exactly the
same.
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How many lasers do you need to make a hologram?
One. However, you can shoot several different holograms on the same
piece
of film. Each holographic exposure can be shot with a different color
laser if, for
example, you are making a multi color image of red, green, and blue. A
color
hologram can also be made with a single laser using tricks of the trade
like
emulsion swelling or multiple reference angles.
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What does the word LASER
mean?
It is an acronym or abbreviation of the first letters of
Light Amplification through
Stimulated
Emmission of Radiation.
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What is colo
r?
Light is a wave. We see differnt sizes of light waves as different
colors.
Its something like the sizes of the strings of a harp making different
musical notes.
The largest strings of a harp make the lowest pitch notes and the
shortest strings
make the highest pitched musical notes. A rainbow is like a harp with
strings of light.
The largest visible light waves are called red.
Those a little smaller are called
orange. A bit smaller and we get
yellow.
Smaller still is green. Smaller once
again and we have blue. And the tinyest
visible
light waves are violet.
Light waves smaller than violet are invisible and called ultraviolet.
Light waves larger
than red are also invisible and called infrared. The visible spectrum
is from
400 nm (nanometers - one billionths of a meter) for violet to 700 nm for
red.
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Is there a word to describe where an image appears in a
hologram?
Yes, there are a few common ones that are quite helpful. If an
image appears
to be on the other side of the hologram, like looking through a window,
it is
called virtual. If an image jumps right out of the
hologram
and appears in front of the film, it is called real,
since it
has left the "virtual" world inside the film and entered the "real"
world. When you flip a hologram over, the image is inside out and
called pseudoscopic
. Flip it back over and view it normally, right side out, and
it is called
orthoscopic. An image can be orthoscopic and real or
orthscopic
and virtual. Or an image can be pseudoscopic and real or pseudoscopic
and
virtual. An image can be both real and virtual, as in the case of an
image
that starts behind the film and then protrudes right out of it.
Holograms
can be made (especially by artists) that have both orthoscopic and
pseudoscopic
images in them. Any combination of these terms is possible. So, to
quickly rehash,
Real = in front; Virtual = behind;
Orthoscopic = right side out;
Pseudoscopic
= inside out.
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How are images made to jump out in front of the holographic
film?
As just explained in the previous response, images that protrude out
in
front of a piece of holographic film are called real
images.
Virtual image holograms are used as the masters for
real
image
holograms. Most real image holograms are holograms of
holograms.
The basic concept is like the idea that a negative of a negative is a
positive. In effect, when you typically make a hologram it is
orthoscopic
(right side out) and virtual (the image appears behind
the film).
If you turn this orthoscopic and
virtual image
hologram over the image you see is both pseudoscopic
(inside out)
and real (in front) since the spatial relationship of
where the
image is seen has flipped. If you usethis image to record a second
hologram, that image will be pseudoscopic
(inside out) because you are recoding the pseudoscopic
image of the
first hologram and virtual. If you then turn it over
it is
orthoscopic (right side out) because an inside out image of an
inside out image is
right side out and real because each time you flip a
hologram over you reverse
from virtual image to real image. Voila!
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Have A Technical Question? Ask Dr.
Laser |
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This page is an ongoing work in progress. |
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© Jason Sapan 2006 |
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