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FREQUENTLY ASKED QUESTIONS

By Jason Sapan / Holographic Studios

  • 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.

 

  • 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.

 

 

  • 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.

 

  • 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.

 

  • 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.

 

  • What does the word LASER mean?
    It is an acronym or abbreviation of the first letters of Light Amplification through Stimulated Emmission of Radiation.

 

  • 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.

 

  • 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.

 

  • 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!

 

 

 

 

 

 

Have A Technical Question? Ask Dr. Laser

This page is an ongoing work in progress.
© Jason Sapan 2003