Professor Edgerton’s Atomic Camera (2006) | Hacker News Reader

Professor Edgerton’s Atomic Camera (2006)

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33 pointsbenbreen13 comments

As of today it should be easy to do a relatively cheap rapatronic-like camera with LCD film.

The basic principle is more or less the same: two linearly (?) polarized sheets at 90° that block all the light going through, and a sheet/material in the middle that rotates 90° the light polarization when an electric current is applied. Some of those glass windows that can obscure instantly work with this technology. https://en.m.wikipedia.org/wiki/Liquid-crystal_display

What I don't know is the speed of polarization rotation for liquid crystals (compared to a Kerr cell) that would define the minimum "obturation" speed available.

A back of envelope calculation for the shutter speed of a Pimoroni LCD shutter [1] suggests 1/15s is the fastest speed available. [2]

[1] Pimoroni LCD shutter [Not available any longer ] https://shop.pimoroni.com/products/lcd-shutter

[2] Testing the amazing Pimoroni LCD shutter https://youtu.be/i3GCfAtdZYI

I've never researched much about this, but this company claims that TN shutters can do up to 100hz and "liquid crystal pi cells" can do 1000hz.

http://www.liquidcrystaltechnologies.com/products/lcdshutter...

This is interesting, I might expend the afternoon reading about it

Edit:

Related 6 years old EE Stack Exchange post: https://electronics.stackexchange.com/questions/276014/chara...

Also this company sells a pi-cell shutter with "50 microsecond rise time 1.3 millisecond fall time" for ~$200USD. I have to calculate the refresh for that : https://boldervision.com/liquid-crystals/pi-cell-shutter/

Auto-darkening welding helmets claim 40 microseconds.

That seems to match with a shutter vendor that says "50 microsecond rise time 1.3 millisecond fall time". So I guess 'rising' is going dark, and 'falling' is going clear.

Or 'rising' means changing the natural state of the crystal (thus rotating 90° the polarization), and 'falling'... well, falling back to the natural resting state. It makes some sense that falling back when unenergized is slower than rising.

Now it'd be interesting to know what happens during rise and fall time. Progressive linear polarization? Waiting time until the crystal reacts?

See https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=81... for examples of modern LCD shutters. They have closing times that are in the hundreds of microseconds, so they are not really replacements for ultra-short exposures. But they are "cheap".

Charles Wyckoff, who worked for EG&G (Edgerton, Germeshausen and Grier), showcasing a rapatronic camera and its peculiar shutter. [1]

[1] https://youtu.be/h0gXivjfh8o

I'd like to see some more photos of the first moments of a nuclear fireball.

You sometimes see video of a nuclear blast; but the first frames just show a ball of plasma that looks like an opaque white cloud. The light from the blast washes out everything else; there's no sense of scale. Is that 100 feet across, or a mile across? And how long ago was the blast?

Slo-mo video, with a size scale and a clock, would be fascinating. But a sequence of rapatronic stills would be very interesting.

> But a sequence of rapatronic stills would be very interesting.

You have a short sequence of stills in the Wyckoff's footage linked somewhere else here. Rapatronic cameras – Wyckoff explains – where typically mounted in a rack of six, where each captured a single frame.

There’s a great sequence here:

https://1.bp.blogspot.com/-CZhjFVVqx6c/TcbXi9tKg8I/AAAAAAAAA...

You can actually see the x rays causing the air outside the bomb casing to glow before the casing is destroyed by the expanding fireball.

More technical info here: https://cinergie.unibo.it/article/view/10328/11419

There are a few in here https://www.atomicarchive.com/media/photographs/testing/us/i...

One interesting tangent to those explosions, is the "double flash" that happens due to the physics of the shell heating rapidly, then obscuring the explosion, then being outrun by the contents.

Even when nations conspire in secret, such explosions can be detected from space.[1]

[1] https://en.wikipedia.org/wiki/Vela_incident

Here's a photo it took nanoseconds after an atomic donation, with some antenna masts in the background for scale:

https://i.imgur.com/nO9gqQp.jpg

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