Forum : Advice & Critiques

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Topic: Photosynth Bullet-Time Rig

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dariusmonsef (Over 1 year ago)
I really want to see this done.  Any ideas how to go about building one on a budget?  Can some point and shoot cameras all be rigged to one remote trigger?  Anyone ever build a bullet-time rig for something else?
tbenedict (Over 1 year ago)
The short answer is yes, some point and shoot cameras can all be rigged to one remote trigger.

Do a Google search for "CHDK".  It's a firmware hack that runs on top of the existing firmware in most Canon compact cameras.  Among other things, it allows you to look at the state of the +5V line on the USB port, and take action based on it.  The upshot is you can set that up to trip the shutter.  I know people have used this to build stereo photography rigs where both cameras trigger together.  I don't know what the practical limit is, though, for the number of cameras you can chain together this way.

CHDK lets you do a lot of other things besides triggering off the USB port, by the way.  Lots of other scripts like intervalometers, focus bracketing, etc. might be useful for Photosynth.


P.S.  What's a bullet-time rig?  Do you mean something along the lines of Doc Edgerton's bullet going through an apple?
JSmith42 (Over 1 year ago)
The movie Matrix is the first (I belive) to feature "bullet time".  Basicly, "time" freezes or slows down while the camera flys around the subject.  In the movie, the effect was all done in computer animation, but people have simulated this real life with huge arrays of cameras all set up to fire off simotaniously or with short delays of a few milliseconds.

Here's the clip from the matrix:

Several games have bullet-time modes... Max Payne, Fear, etc.
JSmith42 (Over 1 year ago)
This video has a good example of a rig:
tbenedict (Over 1 year ago)
Oooh wait a sec.  The shots in the first Matrix movie were done using an array of Canon EOS A2 cameras shooting 35mm film.  Subsequent Matrix movies used a great deal of CG during fight scenes, but that first one used film cameras.  (I remember, because the A2 was my primary camera at the time, so I felt REALLY jealous seeing all those cameras set up for those shots in the special features.)

Compact cameras running CHDK and triggering through the USB port could probably pull that off.  Every camera will have shutter lag of some sort, even the A2.  But using identical cameras, you can likely sync them to that level.

I was just concerned someone was going to try to take a picture of something like a bullet passing through an apple, the way Doc Edgerton did while he was developing the flash lamp.  That's a lot tougher, since you're talking microseconds instead of milliseconds.

But Matrix-style effects are certainly doable with compact cameras.

K (Over 1 year ago)
i was looking at chdk over the weekend and found at least one person who managed to sync 8 cameras to within a 10th of a second.  that means you'd probably want to use a flash to freeze the action.  note that in the video clip jsmith42 shared it looks like they were using around 16 cameras.
dariusmonsef (Over 1 year ago)
Dear Tom,

No firearms will be used :)

Thanks for the info both of you.  I wanted to set something like this up so you could get "action" style synths that can be zoomed and panned around... ie, jumping in mid air (wearing tight latex pants and kicking people in the face optional)
tbenedict (Over 1 year ago)
Hahahaha!  Well, I still think Doc Edgerton would've loved The Matrix. ;)

There may be hope for syncing cameras via CHDK.  One of the CHDK developers is working on a specialized build that allows you to crank up the cycle speed for a given piece of code, so it might be able to get tighter timing on the USB port.  (And that reminds me...  I'm supposed to be doing testing on that build.  DOH!  Ok, I know what I'm doing this weekend.)

drkim (Over 1 year ago)
Harold Edgerton did it as simply as possible...

First, it wasn't the camera he triggered, it was his strobe. The strobe could flash for a much shorter duration than the mechnical shutter could open and close. That's why his images were so crisp.

Second, he just triggered the strobe by setting up a mic to fire the strobe. Then he would fire the gun (through the apple, balloon, whatever...)

To have the image exposed later in the event (like the apple was more destroyed) he would just move the mic farther from the gun. To have the image exposed earlier in the event (like the apple was less destroyed) he would just move the mic closer to the gun. The speed of sound did the rest!
tbenedict (Over 1 year ago)
Thanks for the clarification, drkim.  That technique works just as well for digital as it does for film!  (Now that would be a WILD synth!  A walkaround of Doc Edgerton shot.)

Any word on your setup, dariusmonsef?  I don't have enough cameras to pull something like that off. :(

tbenedict (Over 1 year ago)
One more data point for you:  SDM is a special build of CHDK specifically for doing stereo data making.  Apparently the idea of triggering multiple cameras (beyond two) is part of it:

From what I can see of that set of images on the front page there, the timing is quite tight.

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