7 ms·
A laser pointer at 2B FPS [video]
- mjmas 1y agoThe view from one end of a laser going between two mirrors (timestamp 1:37) is a fairly good demonstration of the camera having to wait for light to get to it.
- Neywiny 1y agoI thought his method of multiplexing the single channel was very smart. I guess it's more common on 2 channel or high end 4 channel scopes to have a dedicated trigger input, which I've checked this one doesn't have. That said, there're digital inputs that could've been used. Presumably from whatever was controlling the laser.
- estimator7292 1y agoFrankly it's uncommon to not have a trigger input. I'm not sure I've ever seen a DSO in person without a trigger in.
- MBCook 1y agoI was confused by that part of the video exactly because I wondered why he wasn’t using the trigger input. Or, would it normally be possible to use a different channel as the trigger for the first channel?
- Neywiny 1y agoI guess I'm used to it. My main scope is an SDS1204 which doesn't have one (and when I inherited it the digital channels were reportedly blown up) despite being fairly capable for its combination of age and price
- dist-epoch 1y agoTechniques like this are/were used to film nuclear explosions (but with a single explosion).
- 01HNNWZ0MV43FF 1y agoScanning a single pixel over an image? How does that work with an explosion? The laser pointer is reproducible
- bob1029 1y agohttps://en.wikipedia.org/wiki/Rapatronic_camera https://en.wikipedia.org/wiki/Rapatronic_camera
- snitty 1y agoBut that bears no relation to what happened in the video.
- masfuerte 1y agoThe rapatronic camera had an incredibly fast electronic shutter. To record a video they needed one camera per frame. Rather like "bullet time" in the movies. The technique in the youtube video is completely different.
- fluoridation 1y agoIt's not completely different. I'd argue it's the exact opposite. Instead of using a single single-pixel camera to record video of a repeatable event, a sequence of regular film cameras captured photographs of an unrepeatable event.
- throw327489 1y agoWho detonated 2073600 bombs?
- 1y ago
- jfengel 1y agoAh, two billion. The first several times I saw this it looked like "twenty eight", which didn't seem terribly interesting.
- tredre3 1y agoThe video is definitely more interesting than 28 fps but it's also not really 2B fps. It captures two billion pixels per second. Essentially he captures the same scene several times (presumably 921,600 times to form a full 720 picture), watching a single pixel at a time, and composite all the captures together for form frames. I suppose that for entirely deterministic and repeatable scenes, where you also don't care too much about noise and if you have infinite time on your hands to capture 1ms of footage, then yes you can effectively visualize 2B frames per second! But not capture.
- gpm 1y agoNah, it's definitely 2B fps, the frames are just 1x1 wide and a lot of the interesting output comes from the careful synchronization, camera pointing, and compositing of nearly a million 1x1 videos of effectively identical events. And there are 1 million milliseconds every ~15 minutes. It doesn't take that long to capture all the angles you need so long as you have an automated setup for recreating the scene you are videoing.
- nkrisc 1y agoEach pixel was captured at 2 billion frames per second, even if techinically they were separate events. Why not call it (FPS / pixels) frames per second?
- ssl-3 1y agoOthers say that you're wrong, but I think you're describing it approximately perfectly. As you say: It does capture two billion pixels per second. It does watch a single pixel at a time, 921,600 times. And these pixels [each individually recorded at 2B FPS] are ultimately used to create a composition that embodies a 1280x720 video. That's all correct. And your summary is also correct: It definitely does not really capture 2 billion frames per second. Unless we're severely distorting the definition of a "video frame" to also include "one image in a series of images that can be as small as one pixel," then accomplishing 2B entire frames per second is madness with today's technology. As stated at ~3:43 in the video: "Basically, if you want to record video at 2 billion frames per second, you pretty much can't. Not at any reasonable resolution, with any reasonably-accessible consumer technology, for any remotely reasonable price. Which is why setups like this kind of cheat." You appear to be in complete agreement with AlphaPhoenix, the presenter of this very finely-produced video.
- MostlyStable 1y agoAs I understand it, this is sort of simulating what it would be like to capture this, by recreating the laser pulse and capturing different phases of it each time, then assembling them; so what is represented in the final composite is not a single pulse of the laser beam. Would an upgraded version of this that was actually capable of capturing the progress of a single laser pulse through the smoke be a way of getting around the one-way speed of light limitation [0]? It seems like if you could measure the pulse's propagation in one direction, and the other (as measured by when it scatters of the smoke at various positions in both directions), this seems like it would get around it? But it's been a while since I read an explanation for why we have the one-way limitation in the first place, so I could be forgetting something. [0] https://en.wikipedia.org/wiki/One-way_speed_of_light https://en.wikipedia.org/wiki/One-way_speed_of_light
- snitty 1y ago>As I understand it, this is sort of simulating what it would be like to capture this, by recreating the laser pulse and capturing different phases of it each time, then assembling them; so what is represented in the final composite is not a single pulse of the laser beam. It is not different phases, but it is a composite! On his second channel he describes the process[0]. Basically, it's a photomultiplier tube (PMT) attached to a precise motion control rig and a 2B sample/second oscilloscope. So he ends up capturing the actual signal from the PMT over that timespan at a resolution of 2B samples/s, and then repeating the experiment for the next pixel over. Then after some DSP and mosaicing, you get the video. >It seems like if you could measure the pulse's propagation in one direction, and the other (as measured by when it scatters of the smoke at various positions in both directions), this seems like it would get around it? The point here isn't to measure the speed of light, and my general response when someone asks "can I get around physics with this trick" by answer is no. But I'd be lying if I said I totally understood your question. [0] https://www.youtube.com/watch?v=-KOFbvW2A-o https://www.youtube.com/watch?v=-KOFbvW2A-o
- evanb 1y agoNo, you cannot escape the conclusion of the limitations on measuring the one-way speed of light. While the video doesn't touch on this explicitly, the discussion of the different path lengths around 25:00 in is about the trigonometric effect of the different distances of the beam from the camera. Needing to worry about that is the same grappling with the limitation on the one-way speed.
- avidiax 1y agoHe did a good job on his setup, but I have to think that adding a spinning mirror would have made everything much faster and easier. He could then capture an entire line quite quickly, and would only need a 1 dimensional janky mirror setup to handle the other axis. And his resolution in the rotating axis is limited only by how quickly he can pulse the laser. Of course, his janky mirror setup could have been 2 off-the-shelf galvos, but I guess that isn't as much "content".
- ahofmann 1y agoBut I think he does capture an entire line quite quickly. As I understood it, he “scans” a line of pixels in seconds.
- kllrnohj 1y agoI think a spinning mirror would make it a lot harder. He's only moving the mirror after the "animation" finishes. So it's capture video, step by 1 pixel, capture video, step by 1 pixel, capture video, etc... He's replaying the scene ~1 million times, for 1 million unique single pixel 2 billion fps videos.
- rcxdude 1y agoBasically the constantly spinning motor would remove the complexity and slowdown of accelerating and decelerating it at the start and end of the motion. To capture a line, he's already scanning it across the scene and triggering the laser at specific points (when the encoder in the servo reaches certain values), if it was continuously rotating he could just do the same thing. Though I don't think it would speed things up much, from what he was saying in one of the appendix videos on his second channel he doesn't do things like triggering the laser multiple times for each pixel to reduce noise because the bottleneck is copying the data off of the scope and it would stretch from hours to days to run.
- MBCook 1y agoAre you suggesting it would be easier if the mirror spun at 2 billion revolutions per second?
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- skopje 1y agoThe triggering scheme is completely brilliant. One of those cases where not knowing too much made it possible, because someone who does analog debug would never do that (because they would have a 50k$ scope!.
- monster_truck 1y agoDoes anyone have a $50,000 scope they could just give to this dude? He seems like he would make great use of it.
- justinator 1y agoI bet we can find 50,000 people with one dollar to give. Let's make this happen HN!
- nerdsniper 1y agoHonestly I think if we each wrote a nice personal letter to Keysight they’d probably gift him one in exchange for the YouTube publicity. Several other electrical engineers on YT get free $20-50k keysight scopes not just for themselves, but once a year or so to give away to their audience members. And yes, this person could make use of it. His videos are among the highest quality science explainers - he’s like the 3B1B of first principles in physics. Truly a savant at creating experiments that demonstrate fundamental phenomena. Seriously check out any of his videos. He made one that weighs an airplane overhead. His videos on speed of electricity and speed of motion and ohms law are fantastic.
- m-ee 1y agoKeysight is not very hobbyist friendly these days. A year or two ago it broke on the Eevblog forums that they were refusing to honor warranties/service contracts unless you had a corporate account with them. If you were just a guy with a scope you would be SOL.
- nerdsniper 1y agoDo you have any better recommendations?
- jval43 1y agoThe original MIT video from 2011: "Visualizing video at the speed of light — one trillion frames per second" https://youtu.be/EtsXgODHMWk https://youtu.be/EtsXgODHMWk (project site: https://web.media.mit.edu/~raskar/trillionfps/ https://web.media.mit.edu/~raskar/trillionfps/) He mentions this as the inspiration in his previous video (https://youtu.be/IaXdSGkh8Ww https://youtu.be/IaXdSGkh8Ww).
- pbronez 1y agoThe slowmo guys did a video about a similar setup at CalTech https://youtu.be/7Ys_yKGNFRQ https://youtu.be/7Ys_yKGNFRQ It’s super cool that AlphaPhoenix is able to get comparable results on his garage. These academic versions use huge lab bench optic setups. They wind up with technically higher quality results, but AlphaPhonix’s video is more compelling.
- brcmthrowaway 1y agoDid he actually repeat the experiment 1280x720 times for every pixel?
- gpm 1y agoIt's pretty clear he had a computer repeat the experiment that many times in reasonably rapid succession rather than doing it "himself", but yes...
- generuso 1y agoYes, the laser was fired at 3 KHz, while the mirrors were slowly scanning across the room. For each laser pulse, one microsecond of the received signal was digitized with the sample rate of 2 billion samples per second, producing a vector of light intensity indexed by time. A large number of vectors were stored, each tagged by the pixel XY coordinates which were read out from the mirror position encoders. In post-processing, this accumulated 3D block of numbers was sliced time-wise into 2D frames, making the sequence of frames for the clip.
- estimator7292 1y agoTl:dw for how this works: He scans one line at a time with a mirror into a photomultiplier tube which can detect single photon events. This is captured continually at 2MSample/s (2 billion times per second: 2B FPS) with an oscilloscope and a clever hack. The laser is actually pulsing at 30KHz, and the oscilloscope capture is synchronized to the laser pulse. So we consider each 30KHz pulse a single event in a single pixel (even though the mirror is rotating continuously). So he runs the experiment 30,000 times per second, each one recording a single pixel at 2B FPS for a few microseconds. Each pixel-sized video is then tiled into a cohesive image
- SCLeo 1y agoThanks for the explanation. Honestly, your explanation is better than the entire video. - I watched it in full and got really confused. I completely missed the part where he said the light is pulsing at 30kHZ and was really puzzled at how he is able to move the mirror so fast to cover the entire scene.
- andrewflnr 1y agoFWIW he explains it better in his earlier video about the original setup. He might be assuming people have seen that.
- alanh 1y agoHuh. I watched a lot, but not all, of the video, and I thought he made it clear early on that he was stitching together 1px videos & repeating the event for each pixel (about a million times for that 720p result)
- easygenes 1y agoGood explanation. One detail though: it is one pixel at a time, not one line at a time. Basically does the whole sequence for one pixel, adjusts mirror to next one, and does it again. The explanation is around the 8 minutes mark. Just want to make it clear that in any one instant, only one pixel is being recorded. The mirror moves continuously across a horizontal sweep and a certain arc of the mirror's sweep is localized to a pixel in the video encoding sequence. A new laser pulse is triggered when one pixel of arc has been swept, recording a whole new complete mirror bounce sequence for each pixel sequentially. He has an additional video explaining the timing / triggering / synchronization circuit in more depth: https://youtu.be/WLJuC0q84IQ https://youtu.be/WLJuC0q84IQ
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- FpUser 1y agoThis video has brough warm and fuzzy memories from my other life. When I was a scientist back in USSR my research subject required measuring ridiculously low amounts of light and I used photomultiplier tube in photon counting mode for that. I needed current preamp that can amplify nanosecond long pulses and have concocted one out of arsenide-gallium logic elements pushed to work in a linear mode. The tube was cooled by Peltier elements and data fed to a remote Soviet relative of Wang computer [0]. OMG this was back in 1979-1981. 0. - https://ru.wikipedia.org/wiki/%D0%AD%D0%BB%D0%B5%D0%BA%D1%82%D1%80%D0%BE%D0%BD%D0%B8%D0%BA%D0%B0_%D0%943-28#/media/%D0%A4%D0%B0%D0%B9%D0%BB:%D0%AD%D0%BB%D0%B5%D0%BA%D1%82%D1%80%D0%BE%D0%BD%D0%B8%D0%BA%D0%B0_%D0%943-28.JPG https://ru.wikipedia.org/wiki/%D0%AD%D0%BB%D0%B5%D0%BA%D1%82...
- -warren 1y agoI'd like to see this with the double slit experiment
- deleted 1y ago[deleted]
- kqr 1y agoIt would look something like this[1] except with slower visual propagation. Note that this camera (like any camera) cannot observe photons as they pass through the slits -- it can only record photons once they've bounced off the main path. Thus you will never record the interference-causing photons mid-flight, and you'll get a standard interference pattern. [1]: https://www.researchgate.net/figure/The-apparatus-used-in-this-article-showing-the-interference-pattern-given-by-a-grating_fig5_243715719 https://www.researchgate.net/figure/The-apparatus-used-in-th...
- gcommer 1y agoAlphaPhoenix mentions in the description that he wants to try and image an interference pattern, and it seems possible. Though it wouldn't really be showing you the quantum effect; that's only proven with individual photons at a time. This technique sends a "big" pulse of light relying on some of it being diffusely reflected to the camera at each oscilloscope timestep. Truly sending individual photons and measuring them is likely impractical as you'd have to wait for a huge time collecting data for each pixel, just hoping the photons happens to bounce directly into the photomultiplier tube.
- ck2 1y agohttps://www.youtube.com/watch?v=sc7FlWUAnzA&t=244s https://www.youtube.com/watch?v=sc7FlWUAnzA&t=244s
- brcmthrowaway 1y agoHow is the image focused and not a big blur?
- kqr 1y agoShere are so many levels this could be answered at. All light in a narrow cone extending from the camera gets recorded to one pixel, entirely independently from other pixels. There's no reason this would be blurry. Blur is an artifact created by lenses when multiple pixels interact. There is a lens in the apparatus, which is used to project the image from the mirror onto the pinhole, but it is configured so the plane of the laser is in focus at the pinhole. What I don't understand is how the projection remains in focus as the mirror sweeps to the side, but perhaps the change in focus is so small.
- slow_typist 1y agoDepth of field, small aperture
- teaearlgraycold 1y agoIt’s in focus because only a small angular area from the scene contributes to the light that reaches the sensor. You get blur when sensor elements (individual pixels) receive light from too wide of an area.
- marshfram 1y ago[dead]
- bjt12345 1y agoCould redshift/blueshift explain why the light appeared to move at different velocity when he moved the camera to another position?
- Tuna-Fish 1y agoNo. It's strictly because of travel time from the "observed spot" to the camera. He explains it in the back half of the video, but for his setup (and every camera everywhere, including your eyes!), it doesn't matter just how long light took to get to the point where it scatters, but also how long it takes for it to get from that point to the detector. If the camera is placed far enough to the side, that time delay is close enough to identical for all samples, but if the camera is in line with the laser, there is a substantial time difference for light scattering close to the camera to light scattering near the far wall.
- Intermernet 1y agoHe actually explains it. It's due to the round trip time increasing from further away water droplets when filmed at an oblique angle. Light hitting a droplet 3m away has a 3x times longer round trip than light hitting a droplet 1m away.
- TheOtherHobbes 1y agoInsanely clever and impressive. Some possible improvements. 1. Replace the big heavy mirror with a pair of laser galvos. They're literally designed for this and will be much faster and more precise. Example: https://miyalaser.com/products/miya-40k-high-performance-laser-light?srsltid=AfmBOoqGv-LiYSdSFbFYAlfCs216njqLVMbIYgNA0ikIGfKjGlzhi4wS https://miyalaser.com/products/miya-40k-high-performance-las... 2. Increase the precision of the master clock. There's some time smearing along the beam. It's not that hard to make clocks with nanosecond resolution, and picosecond resolution is possible, although it's a bit of a project. 3. As others have said, time-averaging multiple runs would reduce the background noise.
- Retr0id 1y agoAt the point where the light is getting reflected on the mirror, it is unfocused - those galvos look too small. But a pair of larger mirrors in the same arrangement could work.
- ky_vulnerable 1y agoCameras really have come a long way since the old 15 FPS movies.
- ck2 1y agolight doesn't move at a fixed rate light moves AT the speed of causality in that frame of time causality appears to have a MAXIMUM limit in this universe in an "empty" void but every time you hear a story of how they "slowed down light" what they actually did is make causality more complex in a dense medium, so slower
- brcmthrowaway 1y agoHow did he determine the principal point to swing around?