Thursday, February 25, 2010

Holograms!

A full set of awesome photos to accompany this can be found on Facebook (public link). There is some basic information there; this entry is more in-depth.

Feeling artsy-fartsy? Wanna play with LASERS? Make holograms! (Disclaimer: this actually takes quite a bit of equipment, which I sadly lack in any independent sense...)

This is the perfect art for people like me: arcane, extremely sensitive, involving complex machinery and glass plates,
shrouded in velvety darkness... there are lenses to adjust and light beams to guide, and at the end, a 3D illusion is captured in your hands.

These holograms (specifically, Denisyuk-type reflection holograms) are physically composed similarly to photographs: a light-sensitive emulsion in a thin layer atop a flat medium. In photos, of course, there's usually a middle step (the negative), and you end up with light-and-dark patterns on paper, whereas in holograms, the light produces ridges in the emulsion that act as highly complex lenses on a glass plate. Technically, the emulsion is also on the back of the plate - with the emulsion on top, you see the reverse image. You can see a "larger" part of a hologram from a small shard because it compares somewhat to a flashlight: your view of the object in that case is akin to a shaft of light beaming into darkness (anything that is not exposed emulsion). The hologram records the interactions between the
reference beam, or the spread-out direct laser beam (which, when you view it, is replaced by your light source) and the object beam, the light reflected back off of the object (which becomes the image you see). You are viewing a reconstruction of how the light reflects off of each part of the object. Since I was using a red laser, the finished hologram reflects this same wavelength of light - so the image looks red. Also, because of how it is constructed, a finished hologram is best viewed under light from a compact point source (like an incandescent bulb).

You may know that the word "camera" is short for "camera obscura", or dark room. Well, when you take a hologram, the entire room literally is the camera, and it contains the plate (vaguely analogous to photo film), darkness, the light source, and your subject. Your setup includes
a laser, a shutter blocking the beam, a mirror to angle it toward your plate, several baffles to block stray light, a spatial filter, the frame that holds the plate, and then your subject. (A diagram can be found here, though the spatial filter is missing - this is what spreads the beam into a cone.)

The spatial filter is a fun piece of equipment, which can take anywhere from a minute up to several tense, fiddly hours to set up. It's essentially a lens, or set of lenses, and a pinhole that you adjust to spread and focus the laser beam
(Mike made ours from old microscopes). The filter has to be aligned vertically and horizontally so that the beam goes straight through, as perfectly as possible, which is the fiddly bit. Once you have this done (on an extremely stable surface), spreading the beam should yield a series of light and dark concentric rings - interference patterns - because the light is passing through a lens. In the center is a bright spot. You move the lens closer to the pinhole until the bright spot is large enough to cover your subject. Then you close the shutter, turn off the lights, set your plate, and leave.

In order to produce a successful hologram of this type, vibrations and environmental light must be minimized. Blocking light is relatively easy: you set up
baffles to keep reflected laser light from hitting the plate, turn off the lights, shut the door, turn off the lights in the next room, and shut that door as well. Blocking vibration is more difficult; Mike Hannum, the awesome Residential College photo/holo prof, built three tables in the basement for this specific purpose. Each one has a bottom layer of 6 inner tubes, then layers of sand and tennis balls for dampening, then more sand and a thick slab of slate on top. It is recommended to work at night, when students are moving around less upstairs and the traffic outside quiets down. And once you've set your unexposed plate in the holder, you leave the room for five minutes to allow the air currents to settle before exposing the plate. Yes. The air currents.

(Do you see yet why I love this art?)

I always picked the table with a shutter switch located outside the room, so I wouldn't have to disturb this setup in order to take the image. Depending on the intensity of the light wash and the reflectivity of the subject, I typically exposed plates for between 5 and 30 seconds. Then, I slunk back into the room, blindly put the plate in a dark sealed box, and brought it out, ablaze with premature triumph. Occasionally, I would end up getting foiled somewhere along the way by developing the plate for the wrong amount of time (this also varies, depending upon the exposure time and such)... but I got some really nice ones along the way, and now I've found my favorite test plates from way back. These and some project materials are now up online, though most of my project work and some of my best overall holograms have been stored elsewhere or given away.

If you want to make simple 3D images but don't have the equipment, check out this awesome handmade hologram video David showed me a while ago... Also pretty frickin' sweet.

Thursday, February 4, 2010

Juggling balls (Part 1)

Warning: this post may provoke puerile giggling.

Last May, the excellent Bob tried to teach me to juggle. He lent me some balls for the day, and of course I immediately lost one. Now I seem to have recovered from those unfortunate associations, and have been learning to juggle for a couple of weeks. The results are surprisingly marvelous! (YouTube vid. Beware of ball hitting computer at the end...)

These balls are quite heavy, for two reasons: a) it makes them easier to handle as a starting set, and b) the fact that they work my hands/arms is a motivator for practicing. This set is made from latex gloves, filled with (dry) Quikrete. The bag coverings make them easier to handle and much more durable.

Materials: satiny bag, latex glove, Quikrete (and an empty medicine bottle for scooping)

Tie off the fingers.

I used maybe 4 scoops per ball; these photos are of a replacement ball (I lost one), and it ended up larger than the others because I didn't remember how much grit went into the old ones.

Hefty!

Satin-y! (Inside out, so it'll end up pretty. The bag is about twice as large as we need, so I twisted it around and stretched it back over itself, à la breadbags.)

Drawstring pulled tight and knotted; the last step is to tuck it into the fabric so the ball doesn't catch on things.

Final bonus: these make a very satisfying "tup" noise (now that I can actually keep them going without dropping them frequently).

Part the Second coming sometime, in which we explore the more effortful way of making these things...