Peter Waddell

STEREOSCOPIC DISPLAY USING A 1.2-M DIAMETER STRETCHABLE MEMBRANE MIRROR

A glasses-free stereoscopic display has been developed in which a large diameter concave Stretchable Membrane Mirror (SMM) is used both as a viewing screen and optical element. SMMs offer considerable advantages over traditional imaging optics in terms of reduced weight and cost, and are revolutionary in their ability to vary their radius of curvature to give a wide range of mirror f/Nos. This is achieved by controlling the magnitude of an applied pressure difference which acts over an edge clamped metallized polyester membrane, forming the basis of a SMM. A stereoscopic display has been developed in which a 1.2-m diameter SMM is membrane, forming the basis of a SMM. A stereoscopic display has been developed in which a 1.2-m diameter SMM is used. Stereo pairs are projected at the surface of the mirror and viewed through a pari of virtual viewing windows. Such a configuration minimizes light loss, giving a very bright image against the specular reflecting surface of the SMM. The image can be formed in front/on/behind the plane of the SMM, making both real and very large sized virtual images possible. Several formats ranging form simple stereo photographs to live stereo video feed in a telepresence display have been viewed using this system.

Membrane-mirror-based display for viewing 2D and 3D images

Stretchable Membrane Mirrors (SMMs) have been developed at the University of Strathclyde as a cheap, lightweight and variable focal length alternative to conventional fixed- curvature glass based optics. A SMM uses a thin sheet of aluminized polyester film which is stretched over a specially shaped frame, forming an airtight cavity behind the membrane. Removal of air from that cavity causes the resulting air pressure difference to force the membrane back into a concave shape. Controlling the pressure difference acting over the membrane now controls the curvature or f/No. of the mirror. Mirrors from 0.15-m to 1.2-m in diameter have been constructed at the University of Strathclyde. The use of lenses and mirrors to project real images in space is perhaps one of the simplest forms of 3D display. When using conventional optics however, there are severe financial restrictions on what size of image forming element may be used, hence the appeal of a SMM. The mirrors have been used both as image forming elements and directional screens in volumetric, stereoscopic and large format simulator displays. It was found that the use of these specular reflecting surfaces greatly enhances the perceived image quality of the resulting magnified display.

Visualizing cross sections of 3D turbulent flows using a modified white light Lau interferometer

A simple white light fringe interferometer is described, which is capable of displaying the phase information from one plane selected in a fluid. By using the correct optics the plane thickness and its position in the fluid can be chosen. An examination of the optical principles of the Lau type interferometer produced conclusions as to how the unit will be developed in the future. Previously published Lau type interferometers have used small diameter, well corrected, relatively expensive lenses (usually with large f-number) to examine small cross sectional flows. The authors intend to use optically accurate, very large diameter, variable focus, mirror finish plastic membrane concave mirrors of any desired f-number. Such mirrors result in any desired plane thickness in any desired position, for fluid flows of very large cross section. Such an important engineering development is already underway and will be reported in future papers.

Interferometric examination of the vibration modes on stretchable plastic membrane imaging mirrors

The paper describes a simple interferometer which has been used to visualize the airborne noise induced, low frequency, very small amplitude, vibrations on thin plastic membrane mirrors. Plastic membrane concave imaging mirrors are the patented invention of the first named author and have been the subject of papers since 1983. The mirrors have already been used for inexpensive large aperture flow visualization systems and the transfer of images in holography. The mirrors are being used currently for high definition, natural color large aperture stereoscopy and self focused real imaging with no spectator glasses, i.e., 3D imaging systems. As the mirror diameter increases for the same type and thickness of membrane material then the fundamental resonant frequency decreases. For very large diameters the mirrors become susceptible to aerial noise of a few Hertz, this being equal to the fundamental resonant frequency. For the small mirror tested for this paper, the fundamental resonance was approximately 600 Hz. The mirror was, however, continually vibrating due to aerial room noise frequencies of between 1 Hz and 20 Hz. No proper nodal patterns can be seen, these only occur at frequencies above the fundamental. The vibrations are extremely small, requiring an interferometer to visualize and record amplitude and frequency. The vibration energy can be destroyed by several techniques. The mirrors have already been used for long exposure white light reflection holograms, effectively no vibrations at all on the mirror surface, achieved by destroying the vibration energy.

Converging beams for distortion-free imagery in transfer holograms

In order to obtain a distortion-free image when a transfer hologram is replayed by a diverging beam, the original reference beam must be the precise conjugate of the replay beam, i.e., it must converge towards the future location of the replay source. Off-the-shelf collimating mirrors have too long a focal length to achieve this, and suitable custom-built mirrors are heavy and prohibitively expensive. Several methods are suggested for obtaining a suitable beam, including a new type of varifocal pellicular mirror made by stretching a metallized plastic membrane over a circular drumhead and creating a partial vacuum behind it, producing a concave mirror of high optical quality with adjustable focal length.

Checking the symmetry of stretchable plastic membrane concave mirrors using a lateral shearing interferometer

The paper describes a simple to use and inexpensive lateral shearing interferometer for checking the symmetry of optically accurate stretchable plastic concave membrane mirrors. The same interferometer can be used for checking the optical flatness of tensional flat membranes, before they are stretched by air pressure difference into concave mirrors. The interferometer is also capable of examining a very wide range of mirror sizes and curvatures. The interferometer reveals by fringe distortion all the blemishes of the metallized mirror finish membranes. The smallest crease marks, invisible to the eye, now become visible. Dust particles can become trapped between the underside of the membrane circumference and the rim top of the membrane support frame. The particles are seen to greatly affect the fringes locally, but have no affect on the rest of the mirror. Slow changing fringes usually indicate leaks of air into the chamber behind the membrane, causing mirror curvature change; or they can indicate membrane creep. Membrane damping can be examined by shouting at the mirror from close range and noting the time for the fringes to resume their stationary positions. The same interferometer also makes a nice flow visualizer, a truly remarkable and well respected instrument.

The Invention Of Fibre Optics Imaging By Television Pioneer John Logie Baird

Television pioneer John Logie Baird, a Scot from Helensburgh near Glasgow, described in his 1928 British patent No. 285,738 a honeycomb bundle of hollow metal tubes or thin solid rods of various types of glass. The tubes or rods were to be used for dissecting optical images in order to allow an ordered scanning of the dissected image pieces in a T.V. transmitter. Each tube or rod carried one small piece of the total image. The dissected image light passed along the tube or rod length, remaining inside the solid rods by internal reflection. By using hollow tubes Baird could also transmit all wavelengths of infra-red as well as visible light. By using hollow metal tubes Baird had ready made waveguides for the control of centimetric or millimetric radio waves. Bairds tube bundles would appear in publications of 1926, as part of the worlds first military infra-red night vision units. The 1926 apparatus used on infra-red searchlight to illuminate the target, the reflected rays were dissected, scanned in a desired pattern and then converted into visible images by Bairds T.V. unit which was called a NOCTOVISOR (night vision). The range of the unit was stated as being 25 miles.