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Holography - Wikipedia. For the documentary authorship, see Holograph. Typically, a hologram is a photographic recording of a light field, rather than of an image formed by a lens, and it is used to display a fully three- dimensional image of the holographed subject, which is seen without the aid of special glasses or other intermediate optics. The hologram itself is not an image and it is usually unintelligible when viewed under diffuse ambient light. It is an encoding of the light field as an interference pattern of seemingly random variations in the opacity, density, or surface profile of the photographic medium. When suitably lit, the interference pattern diffracts the light into a reproduction of the original light field and the objects that were in it appear to still be there, exhibiting visual depth cues such as parallax and perspective that change realistically with any change in the relative position of the observer. In its pure form, holography requires the use of laser light for illuminating the subject and for viewing the finished hologram.

In a side- by- side comparison under optimal conditions, a holographic image is visually indistinguishable from the actual subject, if the hologram and the subject are lit just as they were at the time of recording. A microscopic level of detail throughout the recorded volume of space can be reproduced. In common practice, however, major image quality compromises are made to eliminate the need for laser illumination when viewing the hologram, and sometimes, to the extent possible, also when making it. Holographic portraiture often resorts to a non- holographic intermediate imaging procedure, to avoid the hazardous high- powered pulsed lasers otherwise needed to optically . Holograms can now also be entirely computer- generated and show objects or scenes that never existed. Holography should not be confused with lenticular and other earlier autostereoscopic 3.

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D display technologies, which can produce superficially similar results but are based on conventional lens imaging. Stage illusions such as Pepper's Ghost and other unusual, baffling, or seemingly magical images are also often incorrectly called holograms. Overview and history.

The technique as originally invented is still used in electron microscopy, where it is known as electron holography, but optical holography did not really advance until the development of the laser in 1. The word holography comes from the Greek words . They were not very efficient as the produced grating absorbed much of the incident light. Various methods of converting the variation in transmission to a variation in refractive index (known as .

Transmission holograms, such as those produced by Leith and Upatnieks, are viewed by shining laser light through them and looking at the reconstructed image from the side of the hologram opposite the source. They are also capable of multicolour- image reproduction.

Due to the shorter wavelength of x- rays compared to visible light, this approach allows to image objects with higher spatial resolution. Mouse Pointers For Vista Free Download. The object in the hologram is a toy van. It is no more possible to discern the subject of a hologram from this pattern than it is to identify what music has been recorded by looking at a CD surface. Note that the hologram is described by the speckle pattern, rather than the . Various setups may be used, and several types of holograms can be made, but all involve the interaction of light coming from different directions and producing a microscopically fine interference pattern which a plate, film, or other medium photographically records.

In one common arrangement, the laser beam is split into two, one known as the object beam and the other as the reference beam. The object beam is expanded by passing it through a lens and used to illuminate the subject. The recording medium is located where this light, after being reflected or scattered by the subject, will strike it.

The edges of the medium will ultimately serve as a window through which the subject is seen, so its location is chosen with that in mind. The reference beam is expanded and made to shine directly on the medium, where it interacts with the light coming from the subject to create the desired interference pattern. Like conventional photography, holography requires an appropriate exposure time to correctly affect the recording medium.

Unlike conventional photography, during the exposure the light source, the optical elements, the recording medium, and the subject must all remain perfectly motionless relative to each other, to within about a quarter of the wavelength of the light, or the interference pattern will be blurred and the hologram spoiled. With living subjects and some unstable materials, that is only possible if a very intense and extremely brief pulse of laser light is used, a hazardous procedure which is rare and rarely done outside of scientific and industrial laboratory settings. Exposures lasting several seconds to several minutes, using a much lower- powered continuously operating laser, are typical. Apparatus. A more flexible arrangement for recording a hologram requires the laser beam to be aimed through a series of elements that change it in different ways. The first element is a beam splitter that divides the beam into two identical beams, each aimed in different directions: One beam (known as the illumination or object beam) is spread using lenses and directed onto the scene using mirrors. Some of the light scattered (reflected) from the scene then falls onto the recording medium.

The second beam (known as the reference beam) is also spread through the use of lenses, but is directed so that it doesn't come in contact with the scene, and instead travels directly onto the recording medium. Several different materials can be used as the recording medium. One of the most common is a film very similar to photographic film (silver halidephotographic emulsion), but with a much higher concentration of light- reactive grains, making it capable of the much higher resolution that holograms require. A layer of this recording medium (e. Process. It is this interference pattern that is imprinted on the recording medium.

The pattern itself is seemingly random, as it represents the way in which the scene's light interfered with the original light source — but not the original light source itself. The interference pattern can be considered an encoded version of the scene, requiring a particular key — the original light source — in order to view its contents. This missing key is provided later by shining a laser, identical to the one used to record the hologram, onto the developed film.

When this beam illuminates the hologram, it is diffracted by the hologram's surface pattern. This produces a light field identical to the one originally produced by the scene and scattered onto the hologram. Vs. This allows the scene to be viewed from a range of different angles, as if it were still present.

A photograph can be recorded using normal light sources (sunlight or electric lighting) whereas a laser is required to record a hologram. A lens is required in photography to record the image, whereas in holography, the light from the object is scattered directly onto the recording medium. A holographic recording requires a second light beam (the reference beam) to be directed onto the recording medium. A photograph can be viewed in a wide range of lighting conditions, whereas holograms can only be viewed with very specific forms of illumination. When a photograph is cut in half, each piece shows half of the scene. When a hologram is cut in half, the whole scene can still be seen in each piece.

This is because, whereas each point in a photograph only represents light scattered from a single point in the scene, each point on a holographic recording includes information about light scattered from every point in the scene. It can be thought of as viewing a street outside a house through a 1.

Making Digital Camera Microscope Adapters Making Digital Camera Microscope Adapters. Richard J Kinch, Ph. D. Last updated: November, 2. Tethering the camera to a PC display is thus desirable with the pivoted orientations.

The adapter shown here couples an HD video camera to this. The eyepiece . This tube would end in an aperture of size about. This choice of. geometry is called the .

The type of cropping. Geometrically. speaking, to establish inscribed cropping, the optics of the adapter scale the. Sometimes the scaling of the circular field may be deliberately shrunk to.

Since location in space involves six degrees of freedom. Precision is not perfection. Since this approach reimplements the eyepiece optics, the expense runs. Clark's notes on the resolution, dynamic range. Neely maintains a detailed page on. AO (American Optical) Spencer Microscope Manuals and Catalogs.

Both influence. the overall length of electrical coupling, however, and they should not. About digital photomicrography? Want to purchase a custom- made adapter? Email me at: kinch@truetex.

Richard J. Kinch. Back to Machine Shop page. Back to Home page. Copyright 2. 00. 2, 2.