Imaging Techniques in Large Format Continuous Wave Holography
The requirement for stability in the CW (continuous wave) mastering process, has a surprisingly beneficial aspect, in that it allows for the utilization of unstable curtained areas to effectively render invisible unwanted elements in the field of vision. This trick is still unique to CW and is sorely missed during Pulse Holography mastering, where the problem is that often too many things are visible and there are limited methods available to conceal them. Thus if a large object is required to apparently float unsupported in space, CW mastering, rather than Pulsed, provides the means to easily achieve this illusion. Many important elements involved in producing high quality large format holograms rest not so much with the traditional concerns of holography but rather with aesthetic concerns that relate to table layout, and lighting techniques that endeavor to feature the subject without visual distractions and to control glare and reflections that lead to non-linear noise.
The specifications of the vertical film alignment in the holographic camera
During the holographic mastering process for large format Rainbow Transmission Holograms the strip of holographic film that becomes the H1 hologram master must be positioned in front of the subject (3D model) in such a way that it is bathed in diffused laser light, but importantly, must be held rigidly and firmly flat against a sheet of glass. Typically, elaborate hydraulic or vacuum systems have been employed to compress holographic film during the exposure process. However this function was achieved at Australian Holographics by the construction of what was referred to as 'the camera'. In fact the camera was a very long and narrow glass box, approximately 2.2 metres long, about 12 cm high and about 6 cm deep. Inside this 'camera' was a loose piece of glass slightly shorter than the length of the camera, but around the same height.
The surprising utility of: Johnson's Baby Oil
The long strip of holographic film was placed between the loose glass sheet and the front of the camera, and the entire camera box was then almost filled with Johnson's Baby Oil. This unusual element to the high tech array of equipment and processes came about after the exhaustive testing of the refractive index of countless varieties of commercially available oils, and to the surprise of the holographers concerned, none could surpass the efficacy of this product. The function of the oil inside the camera was to act as an agent to cause the camera to flatten the film between the two glass surfaces. As the oil slowly seeped out between the film's surface and the two glass sheets the natural viscosity of the oil maintained an ultra-thin but cohesive layer that had the effect of gradually pulling the two glass sheets together with a level of force sufficient to flatten the film to within the tolerance level that allowed a consistent interference pattern to be recorded on the H1 master.
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