brainwagon "There is much pleasure in useless knowledge." — Bertrand Russell


Printing Holograms on a Laser Printer

Well, the other day I was scanning the logs of what people had accessed off my site, and found that someone had apparently found my website while looking Thad Walker's paper Holography without Photography. Walker wrote on how you could write a simple C program (a dubious example was included in the paper) and use it to compute an image which you could then print on a laser printer, and then when you shine a laser through it (in a specific way involving a lens or two, but nothing too fancy), you can get the original image out.

Well, actually two copies of the image, one reversed from the other. And a bright red spot in the middle.

In the post above, I said I should do it sometime.

So I did.

And here it is. You might not be able to tell, but the icon I was trying for was a brain. It actually looks better in real life than it does here, but the resolution is limited to about 60x60 pixels, so I probably should have tried a simpler image. Still, I was kind of pleased with the result, as useless as it is.

When I get the system all worked out and understand the math more, I'll post a more elaborate HOWTO. Till then, try absorbing Walker's paper.

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Worldwide Pinhole Photography Day

Today is Worldwide Pinhole Photography Day: a day where a simple hole and the wave nature of light conspire to create art. I was meaning to construct a simple pinhole camera, but didn't quite get around to it, and today might be too late, but if you are interested, try checking out the forums on for some awesome information.

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I'm killing some time today thinking about how to compute optimal pinhole sizes for specific focal lengths, which leads rather naturally into the possibility of computing zone plates for as well. Note: there are no shortage of formula, none of which really agree, to compute optimal pinhole size, I want to derive them from principle. I'll let you know what I find out.

My Desk, ala Pinhole Photograph
Above is my sole noteworthy pinhole photograph, taken from a simple cylindrical camera (hence the slightly wacky distortion) onto some kind of Ilford photographic paper, scanned, and inverted in Photoshop. I'll try to put up a picture of the camera later.

Addendum2: Here is the Flickr stream for pinhole photographs.

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Digital Inline Holography with a Laser Pointer

I hadn't heard of inline holography before, but apparently it was proposed decades ago by a short article in Nature by Gabor. Basically it is a technique by which interference patterns between an object and a reference wavefront is recorded, and then reconstructed in using clever math and the FFT.  Very neat.  Laser Pointer Holography

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little tips about making rc micro_helicopter

It's been a busy week for me, wading through piles of SIGGRAPH sketch reviews, so I haven't had too much inclination to spend more time in front of a computer.   But I did find this article linked on the make blog: little tips about making rc micro_helicopter.  A very cool micro helicopter, which used a CDROM drive motor for the main drive.  Very cool.

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SIGGRAPH 2006 Papers

This week I'm busy at work trying to complete dozens of SIGGRAPH sketch reviews, so it seems like an opportune time to present the usual link to  online copies of the SIGGRAPH 2006 Papers that have been accepted.  I haven't had a chance to review these yet, but there is usually something good in this pile.

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Gutenberg Gem: Latin for Beginners by Benjamin Leonard D’Ooge

Latin for BeginnersEver wanted to learn Latin? Well, perhaps it is just me then, but if you ever had the urge, you can check out Latin for Beginners by Benjamin Leonard D'Ooge courtesy of Project Gutenberg.

Perhaps then you could figure out:

Antiquis temporibus, nati tibi similes in rupibus ventosissimis exponebantur ad necem.

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From bits to bytes…to bots

Apparently Bruce Shapiro was showing his "eggbot" at the Maker's Faire, but I didn't get a chance to see it.  But his instructions online give many details of how you might actually do something like that, and it all seems very clear and straightforward.   Interesting.

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I made the big time!

Engadget loves me!Engadget mentioned me in their Maker's Faire writeup!

Yes! Front row!

I hope my poor little server can handle the strain!

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Addendum: For those of you who didn't get to see this or talk to me, here is a brief writeup. Check the bottom of that page for a link to the PDF file I was handing out to explain why I did the project, and the links to the hardware and software that I used.

Addendum3: If you want the source and the binary file that you can run with Stella, click here to download the zip file. Feel free to do whatever you want with it, as long as you keep the copyright intact.

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Dear Lord: Why are your minions so stupid?

What kind of blunt force trauma made someone stupid enough to actually publish this?

Math Proves Christ's Resurrection?

[Via Good Math, Bad Math.]

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Maker’s Faire Update

Well, I spent all day yesterday demoing my Enigma 2600 project in Hall A at the Maker's Faire. I printed out sixty little info sheets and some business cards that described the project, and somehow got it exactly right: I gave away my last one just minutes before the end of the show. My voice is thoroughly trashed from talking, but today I'm thinking about just going down and seeing what everyone else is showing. The event seemed really fun, and I loved everyone's enthusiasm level. I even met someone who designed video games for the Atari when it was still a viable commercial product.

I'll post another update after today's show.

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Metagrrrl snapped this picture of me at the Maker's Faire

Addendum: Metagrrrl snapped this pic of me explaining my silly Atari project to her friends. Check out her Flickr stream for more.

Addendum2: My silly cat has gotten in yet another fight, and his leg looks swollen and sore, so today's Maker's Faire will be preceded by a trip to the vet for some antibiotics. Silly kitty.

Woz gets dunked for the EFF

Addendum3: Silicon Valley legend Steve Wozniak was on hand for a chucker of Segway Polo, and decided to cool off by helping to get donations for the EFF by submitting himself to repeated showers of water. Well done Steve. You got my donation.

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Scoring a Baseball Game ala Project Scoresheet

David Cortesi has a nice page on scoring baseball games.  I haven't done this myself, but I think it might be a cool way to record games that you enjoy and keep you focussed on the action around you.  David uses the Project Scoresheet way, which records more information than traditional scoresheets do, and are amenable to input to computers for further analysis.

His writeup seems very nice.

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The Enigma 2600

Enigma 2600I'll be showing off my Enigma 2600 at the Maker's Faire this Saturday in San Mateo. Click on the link to read more about the project: I hope to see some of my readers there.

Addendum: I'll shoot some more pictures tonight for the page.

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Gutenberg Gem: Raggedy Ann Stories, by Johnny Gruelle

Raggedy AnnChildren's books are kind of cool, especially for the illustrations. Try checking out The Project Gutenberg eBook of Raggedy Ann Stories, by Johnny Gruelle for a nifty, fun example.

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The 1906 San Francisco Earthquake and Fire

Fire along Market St, San Franscisco, 1906Today marks the 100th anniversary of the San Francisco Earthquake and Fire. The best online resource is the Bancroft Library at Berkeley, which has over 17,000 photographs collected and available online.

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I found the following chart of post office branches that will remain open late useful.   Unfortunately.

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