...we can unobtrusively tag the world, so that [our] phones, computers, or other devices know what's in the environment and where. One simple app is to overlay product information (dietary info, recipes, reviews, commercials (think dancing bears attached to the box!) etc over the packages on the store shelves. Because you can sense multiple bokodes at once, you can compare products.
          - Quinn Smithwick of the MIT Media Lab
              from a recent interview with Robert Evans

Understanding what the folks over at MIT's Camera Culture Group inside the Media Lab have done to create their Bokode system takes a good bit of mathematics and a healthy enthusiasm for optics. However, understanding what it can do and what the potential exciting applications are only requires a video. I was immediately fascinated with the project mostly for its magic trick element. It conveys its secret information to anyone who knows the trick. I read the material MIT published, and frankly there is quite a bit, and thought finding a low tech way to play and spread the technology around would be pretty fun.

Bokode is a method MIT developed for tucking information (such as barcodes, images, etc. in microprint) into a tiny but easily visible package. It leverages the bokeh effect to show off the information on the microprint to anyone pointing a camera at the Bokode unit and defocussing. If you've ever taken a photo with a distant city in the background and noticed the city lights turning into little circular blobs when out of focus you've seen the bokeh effect. The light blobs are sometimes referred to as circles of confusion. Using a tiny lens inside the Bokode unit this circle of confusion can show the information on the microprint. The Camera Culture Group goes into great detail to explain the mathematics behind the effect. I'm going to demonstrate a simple method to recreate the effect at home using some easy to find materials. The one difficult part of the whole project is making microprint. I got my sheet made at Pageworks to the tune of $70. If you just want to look at some really tiny things with the lens I'd suggest cutting yourself a little square of dollar bill and looking at its tiny printing through the unit. Much cheaper.

Video showing the effect at ~3ft

To observe Bokode in action you need a unit consisting of a lens, the pattern to be viewed, a diffuser, and an led (you can download my diagrams here.) There are some photos of the unit up on Flickr. If you happen to own a laser cutter you can download a laser cut version of the unit here.

I pulled my lens out of a webcam. I went around to some local cellphone shops asking for broken cameraphones. The lenses from these worked but are so tiny they seldom showed the effect with much conviction (though the Motorola Razr won for largest lens.) It seems like the average webcam has a lens diameter of about 3mm, so it's my pick for cheapness and ubiquity. Since the size of the lens inside the Bokode unit is directly proportional to the amount of visible microprint, I found the larger webcam lens to be a huge improvement. Most webcams also house their lenses in a convenient package that's really easy to remove and insert into the Bokode unit. I also wrapped a bit of tape around the portion of the webcam lens that fit into the unit so I could do some fine adjusting to the focus. It's fairly easy to put your eye up to the lens, do a rough focus, and then focus once more with the camera about a foot away from the unit.

Some other features that control how strongly the effect appears are the aperture size of the camera you use to view it and the distance you are from the unit. Since magnification is more or less focal length (the distance from your camera to the Bokode unit) divided by lens diameter, magnification increases as you pull further away from the unit. That means, in my setup, viewing the effect at one foot away was about 100x magnification. Cameras that use small apertures (webcams, cameraphones, your eyes, etc.) won't be able to make out the effect. Essentially you need a decent digital camera to make it work. I've observed the effect with max zoom on infinity focus with both a Sony DSC-H5 and a Cannon Powershot.

You can download some of my sample patterns here. I made mine by creating new 2cm x 2cm bitmap documents at 5080dpi in photoshop, drawing patterns with the pencil tool, and exporting them as EPS files. I then assembled them into in Illustrator and sent Pageworks a PDF. I'd recommend keeping pattern unit sizes to about 100um and keeping away from grainy images. The print has a tendency to bleed together if you try to get details of one pixel.

This whole project wouldn't have been possible without the work of the Camera Culture Group. It's their concept and their technology. A special thanks goes out to Grace Woo and Ramesh Raskar for their advice. Some of my other projects can be found at sinbox, instructables, and flickr. You might consider following me on twitter.

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