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A laser pointer at 2B FPS [video]

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Re: A laser pointer at 2B FPS [video]

#81

Post by easygenes »

generuso wrote: post #65
userbinator wrote: post #63

Earlier quoted context omitted.

I believe this technique is known as "equivalent-time sampling".

The author uses "real time sampling" to acquire evolution of light intensity for one pixel at 2 GSps rate. The signal is collected for approximately one microsecond at each firing of the laser, and corresponding digital data is sent from the oscilloscope to the computer. "Equivalent time sampling" is a different technique which involves sliding the sampling point across the signal to rebuild the complete picture over…

I think parent meant that the image construction technique is analogous to equivalent time sampling. You’re correct in the mode of the oscilloscope’s use. However, the mode of the larger system is using a repetitive signal and sliding sampling points across it.

Re: A laser pointer at 2B FPS [video]

#82

Post by easygenes »

nerdsniper wrote: post #64
m-ee wrote: post #61

Earlier quoted context omitted.

Keysight 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.

Do you have any better recommendations?

They’re not one of the big 3, but Rigol are pretty much the only scope co actively marketing models to hobbyists / individuals: https://www.rigol.com/europe/news/company-news/mho900-releas...

Re: A laser pointer at 2B FPS [video]

#83

Post by Neywiny »

estimator7292 wrote: post #31
Neywiny wrote: post #3

I 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.

Frankly 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.

I 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

Re: A laser pointer at 2B FPS [video]

#84

Post by pbronez »

jval43 wrote: post #25

The original MIT video from 2011: "Visualizing video at the speed of light — one trillion frames per second" https://youtu.be/EtsXgODHMWk (project site: https://web.media.mit.edu/~raskar/trillionfps/ ) He mentions this as the inspiration in his previous video ( https://youtu.be/IaXdSGkh8Ww ).

The slowmo guys did a video about a similar setup at CalTech 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.

Re: A laser pointer at 2B FPS [video]

#85

Post by freetime2 »

tredre3 wrote: post #23
jfengel wrote: post #6

Ah, two billion. The first several times I saw this it looked like "twenty eight", which didn't seem terribly interesting.

The 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…

I would probably call it 2 billion fps* (with an asterisk), with a footnote to explain how it’s different than video is typically captured. Especially the fact that the resulting video is almost a million discrete events composited together as opposed to a single event. All of which the video is transparent about, and the methodology actually makes the result more interesting IMO.

I would say that everyone - you, other commenters disagreeing with you, and the video - are all technically correct here, and it really comes down to semantics and how we want to define fps. Not really necessary to debate in my opinion since the video clearly describes their methodology, but useful to call out the differences on HN where people frequently go straight to the comments before watching the video.

Re: A laser pointer at 2B FPS [video]

#86

Post by Retr0id »

TheOtherHobbes wrote: post #79

Insanely 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-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 resoluti…

At 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.

Re: A laser pointer at 2B FPS [video]

#87

Post by beowulfey »

tredre3 wrote: post #23
jfengel wrote: post #6

Ah, two billion. The first several times I saw this it looked like "twenty eight", which didn't seem terribly interesting.

The 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…

A frame is by definition flexible in how many pixels tall or how many pixels wide it is, and there is nothing in the definition that says it can't be 1x1.

Re: A laser pointer at 2B FPS [video]

#88

Post by rcxdude »

avidiax wrote: post #10

He 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…

Yeah, spinning at a constant rate with an encoder for triggering would probably be a bit more consistent. But potentially more of a mechanical headache. And he does need a pretty big mirror due to being limited by the amount of light he can focus on the sensor, I'm not sure that there are galvos available with such a large area (especially for a reasonable price).

Re: A laser pointer at 2B FPS [video]

#89

Post by rcxdude »

kllrnohj wrote: post #16
avidiax wrote: post #10

He 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…

I 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.

Basically 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.

Re: A laser pointer at 2B FPS [video]

#90

Post by MBCook »

db48x wrote: post #48
MBCook wrote: post #44

Earlier quoted context omitted.

I 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?

He explained that. His inexpensive oscilloscope _can_ trigger from the second channel, but only at one billion samples per second. Where’s the fun in that?

Oh that’s right. I saw this video earlier in the week and forgot that.

Thanks.

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