While I was attending Antioch West/University Without Walls in San Francisco in 1972, Lloyd Cross, Jerry Pethick, and Gary Adams of the San Francisco School of Holography put on a demonstration at Antioch West's administrative headquarters. The holograms they brought were mounted on pedestals made from large cardboard tubes. Each tube held a 1 or 2mW HeNe laser used to reconstruct the holograms. The holograms were very clean (noise-free) and bright. Cross gave a short lecture illustrated with charts and invited Antioch/West students to attend the School of Holography's Basic Holography course. A classmate, Lon Moore, had been prodding me to attend, and this demo pushed me over the edge. Fascinated, I signed up for the next Basic Holography course.Warehouse in the Mission District
The School of Holography was located in a cavernous warehouse on Shotwell Street in the Mission District. The enormous space was divided roughly down the middle -- the left half consisting of a workshop, darkrooms, and a small "classroom" area in the back. The right side was used as a display area, meeting room, and living space for some of the SOH denizens (Sharon McCormack, Rufus Friedman, Michael Kan, Alan?, Gary Adams, Jerry Pethick, Lloyd Cross, Lon Moore, Fred Unterseher, Pam Brazier, Dave Schmidt, et al). Since darkrooms areas were interspersed throughout, the lighting was subdued and indirect, further enhancing the cavern atmosphere.Sandbox Holography
Holography typically requires manipulating the laser beam with lenses, mirrors, beamsplitters, pinholes, etc. All of these elements must be positioned in space and held steady to within about 1/100,000 inch for up to several minutes. To accomplish this task, most traditional optical laboratories use expensive micro-positioning mounts to hold the optics. To isolate the optics from room vibrations, they are mounted on a foot thick granite slab floated on compressed nitrogen pistons. These set-ups cost many thousands of dollars.
Jerry Pethick suggested a much simpler but equally effective system using sandboxes floating on automobile innertubes. A 4X6 foot or 4X8 foot slab of concrete was poured and a 2 foot deep box made of cinder blocks was built on top to hold the sand. The slab and box were then floated on innertubes for vibration isolation. Optics were mounted on the ends of 2 inch diameter PVC pipe sunk into the sand. With Pethick's method, adjusting the position of the beam was simply a matter of moving the pipes in the sand. Once released, the pipes held their position. After making all the adjustments, we tapped the pipes with a finger to give them a final "set", then let the table "settle" for 30 minutes before exposing a hologram. I saw several very high quality 8X10 holograms made with this system using small 1mW lasers with 5 minute or longer exposure times.
Lloyd later modified the stable table design by eliminating the concrete blocks. Instead, he used heavy particle board clamped into a "tension structure". Particle board has many advantages in holography: it's cheap, uniform, dense, stable, and free of internal resonances. Lloyd successfully used this "tension structure" concept for many different stable rigs in holography. An excellent example is the MarkIII Multiplexing Camera.Basic Holography Class
By the time I signed up for the class, Cross had delegated teaching Basic Holography to previous graduates or "interns" in exchange for studio time. Cross presented the initial "lecture" in the back of the warehouse. His simple, yet elegant presentation covered the basics of lasers, interference, and wavefront recording/reconstruction. After the lecture we headed for the sandboxes to construct interferometers. Over the next sessions the "interns" guided us through single beam, split beam transmission, and finally split beam reflection holography.Laser Light Show Gadget
Earlier in 1968, Lloyd had invented "Sonovision" a method of modulating a laser beam via sound. There was a fellow at the SOH named Alan who had worked with Lloyd in Ann Arbor. Together they built a nifty laser beam modulator for laser light shows based on Lloyd's Sonovison. Alan cast a thin flexible membrane (Silicone?) over the front of an ordinary speaker cone. He then cemented a small (Mylar?) mirror in the center of the membrane. The speaker was then connected to an audio source, and a laser beam was reflected from the mirror. The reflected beam created a dynamic Lissajous-like pattern on the walls and ceiling in sync with the music (or other sound). In the SOH cavern this was very effective for spontaneous parties and dances. Although today this gadget seems obvious, at the time it was a new concept. Allan spent many days experimenting with speakers and the membrane material. I believe they sold a number of these gadgets.Knowledge is Free
Lloyd believed very strongly that knowledge should remain free. Maybe he felt that it was OK to charge money for the acquisition of knowledge. This paradigm created many challenges for the survival of SOH. I can remember a stretch in 1974 where the entire "staff" of SOH would meet for hours on end for intense discussions of non-traditional options of organization, revenue generation, ownership, knowledge, etc.Full Color Holograms
Somehow SOH acquired a large Krypton Laser. This was only used for rare demonstrations as Lloyd once told me it cost $10 a minute to operate. It used something like 20 gallons a minute of cooling water and 200 Amps of power. The advantage of Krypton is that it can be tuned to produce a number of lines spanning the visible spectrum, thus making it suitable for full color holography. At that time Kodak produced the 649F plate which was I believe panchromatic. There was some talk at SOH of attempting full color reflection holograms with these plates using the Krypton laser. But these plans evaporated when the idea of multiplexing came along...Multiplex Holography
Sometime in late 1973 or early 1974, Lloyd and the SOH group began constructing a system to multiplex many 2D images into a 3D image. (This idea was first suggested by DeBitteto back in the 1960s). The first incarnation of this system, the Mark I, was built on the floor just beyond the workshop. I only remember it as a squat Rube Goldberg-like contraption. I believe it used some large glass lenses as part of the projection optical train. Lloyd, Gary Adams, Michael Kan, and Lon Moore fussed over it for some time. Ultimately they produced a cylindrical transmission type hologram from a series of motion picture frames. Dr. Tung Jeong, a prominent holographer from Lake Forest College visited about this time and revealed his plans for a similar device which used Fresnel lenses as the projection optics. By this time, though, Lloyd and the crew were beyond paper plans -- they were actually producing holograms.
Also about this same time, Steve Benton at Polaroid invented a new method called "rainbow" holography which allowed holograms to be reconstructed in white light. The trick was to eliminate vertical parallax, but retain horizontal parallax. When reconstructed with white light, the image smeared into a rainbow up and down, but was fully 3D in the horizontal plane. So long as your eyes remained horizontal the effect was stunning. What a revolution! Benton visited SOH and showed his new hologram, though he offered no explanation of how it was produced. The place was abuzz for days.
Lloyd pondered the rainbow hologram for a few days, then promptly produced an example in a sandbox. The trick was to produce a master hologram of the subject, then create a secondary focused image hologram by reconstructing only a tiny horizontal section of the master hologram. At first the reconstructing beam was masked down to a thin stripe with an aperture. Unfortunately, the process of masking the beam wasted a lot of light. Later Michael Kan devised a clever method of producing a thin horizontal beam using two convex lenses. He canted the first lens at about 30 degrees, and by manipulating the distance between the lenses, produced a bright, thin horizontal beam with no light wasted.The Multiplex "Camera"
Armed with the new rainbow technique and new ideas on liquid lenses, tension structures, slit optics, etc., Lloyd and the SOH crew set out to build the Mark II multiplexing camera. The Mark II was constructed of particle board sub-assemblies held together with threaded rod clamps in a "tension structure" and floated on small airplane tire inner tubes.
The subject of the hologram was filmed with a 35mm motion picture camera while being rotated on a turntable. Each frame of film corresponded to 1/3 degree of rotation. I believe they used Eastman Double-XX film.
The 35mm motion picture film positive print was then loaded into a particle board projector at one end of the Mark II multiplex camera. The projector used a unique pull-down mechanism to gently advance each frame and hold it in place for projection onto the holographic film.Liquid Lenses
Lloyd planned to generate a "rainbow" hologram in one step by projecting the film frame through a large aperture collimator, and then compressing the image horizontally with a second large aperture cylindrical lens. To achieve the large aperture required using "thick" lenses with a clear aperture of over 9 1/2 inches (the width of the holographic film). The cost of grinding glass lenses to these specifications would be enormous, so Lloyd proposed fabricating a pair of liquid filled cylindrical lenses. The axes of the lenses would be orthgonal-- collimation would be performed by both lenses, and the horizontal compression would be performed by the second lens. I believe the focal point was actually slightly in front of the film.
Back in the early 1970s, desk top computers were not common, so Lloyd used a pocket calculator to compute the required lens curvature. Though I don't understand the math, apparently it required a long series of iterative steps requiring several days of tedious calculation. I remember him seated in an old chair punching in numbers.
The lenses were fabricated by bending optical grade plexiglass to the desired curvature to form a hollow chamber. The chamber was then filled with high grade mineral oil. Adjustments on the top and bottom of the frame holding the plexiglass were provided to "tune" the lenses and remove sag. Considerable effort was expended in coming up with a sealing mechanism to prevent the mineral oil from leaking. I believe Dave Schmidt made significant contributions to the seals.
Tuning the lenses required considerable skill as I later learned first hand. To the eye, the lens might appear fine, but invisible phase changes played havoc on the laser image. Each "warp" had to be carefully tuned out with tiny adjustments to the lens curvature. Between adjustments, the lens required a "settling" time to come to equilibrium.
The 9" high holographic film was placed in a cylindrical film platen made of plexiglass on an indexing table. The film extended over a 120 degree semi-cylinder. The indexing table, also made of particle board, used a door spring as the ring gear. Lloyd shimmed it along its length to exactly adjust the travel. An off the shelf worm gear drove the door spring gear. The entire mechanism from projector to film platen was controlled by a system of solenoids and motors controlled by a bank of rotating particle board cams with switches. To adjust timing required changing the speed of the DC motor with the rheostat and/or adjusting the duration of the cam.
The reference beam, compressed into a slit with Mike Kan's clever optics, was brought in from overhead, making it necessary to record the image upside down to get a hologram which reconstructed from below.The "Kiss"
The first major effort
was the famous "Kiss".
This fabulous image depicted Pam Brazier blowing a kiss as you
walked around the hologram. In short order the SOH produced a
number of different multiplex holograms and attempted to create
a business. But that's another story...