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Comment by bombela | Hacker News Reader

7mths? What unit is that. Did they mean 7μs resolution? How is that special? I see youtubers doing nanoseconds.

edit: here is the important information in this article.

> Scorpius is a new accelerator project planned for the Nevada National Security Site (NNSS) that will use an electron beam that can be broken into customized pulses to deliver x-rays and capture multiple images only hundreds of nanoseconds apart.

So 0.1μs or 100ns temporal resolution 3D X-ray.

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While we're nit-picking the title, what does the "real-time" part mean? How would it be different if it wasn't real-time?

Dictionary.com defines "real-time" like as, "the actual time during which a process or event occurs", eg "along with much of the country, he watched events unfolding in real time on TV". Or in the domain of Computing, "relating to a system in which input data is processed within milliseconds so that it is available virtually immediately as feedback to the process from which it is coming, e.g. a missile guidance system might have "real-time signal processing".

Neither definition work here. It seems like they took a sequence of pictures very quickly, and then, some time later, played them back at an enormously slowed-down rate.

The opposite of "real-time" in this context would be "sampling". It means that the capture represents the high-resolution time history of one particular event (one explosion) instead of fast and successively offset captures from as many events.

The first line of the articles says "seven-millionths of a second", which would be 1/7μs or 0,14μs. They also mention that the camera shot 16 frames in that period, so that would be once every 0,00875μs or once every 8,75ns

Youtubers are a couple of magnitudes away from that, AFAIK

I would say you described "one seven millionth" of a second (1/7,000,000 s)

"Seven millionths" would be 7/1,000,000 s (7μs). They take 20 to 40 images in that period using 7 cameras, so any given camera might be as low as 1.4μs per frame.

Saying ~140k photos per second would have been a more understanding stat if only the article framed it that way.

Yes, but they said seven-millionths of a second, not seven millionths of a second. Technically they're right that that's what it means, but I'd expect an editor to recommend against that phrasing in favor of the one you used to avoid confusion.

Well, it's true that the article says "seven-millionths".

I would guess it's a lot more likely that this is an editing failure, introducing a hyphen where no hyphen should be, than that they meant to divide a second into seven million equal parts.

For one thing, as SECProto alludes to, English would normally require you to say "less than a seven-millionth of a second" if that was what you meant. There's no such thing as saying "less than weeks". You have to specify less than how many weeks.

    less than (seven) (millionths of a second)

ordinary grammar, ordinary unit choice

    less than (seven millionths of a second)

improper grammar, bizarre unit choice.

I agree based on the whole sentence in the article that that was probably an editing error.

The slow mo guys did a video [1] at 10 trillion FPS. They also recently did another video [2] at 5,000,000 FPS. Their other videos vary between 50,000 FPS and 850,000 FPS.

Edit: They mention in [2] that the Phantom camera they have can go to a 95ns exposure up to 1,750,000 FPS.

[1] https://www.youtube.com/watch?v=7Ys_yKGNFRQ&pp=ygUMc2xvdyBtb...

[2] https://www.youtube.com/watch?v=BTkZ36g4GOs

The 10 trillion FPS number comes from the fact that they’re taking advantage of a strobing effect in the light they’re filming, such that if the strobe is happening at (for example) 1000Hz, they can get a frame at time T, then a frame at time T + 1.00000000001ms, then T + 2.00000000002ms, and so on. Then you stitch it together and it looks like they’re a 10-trillionth of a second apart.

No camera is taking in 10 trillion frames of data per second.

"electron beam that can be broken down into customized pulses" also sounds superficially like strobing.

Not with X-rays they aren't.

I understood the article just fine, despite the spurious hyphen. The HN title could be improved immensely if it just said 7 microseconds.

I think this is incorrect reading of the numbers

I've never heard of `{number} {plural magnitude}` meaning `mag / number`. I've only ever seen it mean `number * mag`. As in 3-thousandths == 3 * 0.001 not 0.001 / 3.

7 * 0.001ms = 0.007ms or 7us or 7000ns.

I read it as months. Super confusing.

7 months/seconds - Its both a dimensionless quantity and a variable. Very impressive. Los Alamos is taking the USA's 'anything but metric units for measuring' to new levels.

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