OT: Optics/Physics question

The camera shutter is open for a (relatively) long time. That is why you see the light from the muzzle flash.

Probably. An interline-transfer CCD, or some types of CMOS sensor, can have really fast shuttering. You'd give it one clock to transfer sideways from the light pixels into the (shielded) transfer array, then shift it out slowly to keep the noise low.

The shutter speed was probably faster than the flash.

Cheers

Phil Hobbs

The flash is MUCH faster than the shutter.

It was an air-gap flash.

Note the fact that you can see the flame, and you can see the bullet without any visible streaking or blurring.

You can get shutter speeds of 1 us with an interline transfer CCD. What sort of flash are you thinking of?

Cheers

Phil Hobbs

You can see from the lit gasses that the exposure is in the ms range but the bullet is completely stopped. You can even see the rifling lands on the bullet.

It is an air spark gap discharge lasting less than a microsecond. I'd bet it is using a standard consumer CCD camera. In a dark room, you open the shutter when the when the trigger is pulled and after a delay, the flash is fired.

I do the same thing with a flash x-ray and an ordinary Nikon digital camera. The x-ray pulse is only 60 ns long.

It's pretty neat. If you are versed in using high voltage, anyone could set it up with little funds. Look up "Marx" generator.

tm

Typical values are 0.05 µF capacity, 0.02 µH inductance, 10 J energy,

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I think a flash sync at these speeds would be difficult, so I vote for the darkened room and the fast flash. Then again, I voted for Gore, so I am used to my vote not counting.

My doubts lie with the timing. This because I notice the (gunpowder) flash coming from around the cylinder but not out of the muzzle. Something "closed that shutter" before that happened because the flash does not illuminate the "flame" of course.

Based on that do you conclude the bullet seen in the photo was not the one that was fired by the explosion that caused the flash from the back of the barrel? for do you have some other explanation for that.

sed

the

The image is referenced by this article:

which explains the timing.

The shutter never closed- the flash was triggered by a microphone and the camera registered everything illuminated by the flash *and* everything tha t provided its own illumination while the shutter was open. Notice the flam es/smoke issuing from the cylinder-frame gap are slightly blurred because t hey moved while the shutter was open.

Also, what do you mean, no muzzle flash?

Mark L. Fergerson

Why doesn't the backflash [burning gunpowder] extend OUT of the muzzle as if the hot gases were 'blowing' the bullet form the barrel? I opt for two pictures overlayed. The 'lighting' on the bullet does NOT look like the lighting on the barrel.

Anybody do image analysis to check for overlays?

Then again, it doesn't matter. It's a 'pretty' picture, well, except for the bothersome feature of the depilatory deficient hand.

Getting the flash to decay fast enough is the parlour trick. Flash x-rays are a lot easier in some ways.

Cheers

Phil Hobbs

A fellow engineer at Motorola, Reuben Wexler (amazed I can bring back that name from memory after nearly 50 years :-), was trying to control the duration of a flash tube, He came wandering thru my lab one day and we discussed his problem. I sketched a bypass scheme on the back of an envelope (*), and promptly forgot about the whole thing.

A few years later I was amazed that a patent showed up in my name...

That snuffs the current flow, but I have no idea about any after-glow.

(*) That's the same way the 1488/1489 RS-232 driver/receiver chips happened. Wasn't even my department, but I did another back-of-the-envelope sketch, and a week later I was assigned the project ;-) ...Jim Thompson

That looks to me like a simmer circuit, which is primarily used to reduce the turn-on jitter of flashtubes, by making sure there are enough ions in the gas to start the avalanche as soon as the main pulse appears.

When that SCR fires, all the energy in capacitor 10 will get dumped into the flashtube, with no way to turn it off till it gets below the holding current. In this case, it was maybe to improve tube life by avoiding sparking at the initial trigger, but it isn't an automatic exposure device, for sure.

Doc Edgerton invented the automatic-exposure flash, using a second, lower-voltage tube in parallel with the first one, and covered with a light shield. When the second tube fired, it hogged all the current from the first one, and so turned off the light.

Cheers

Phil Hobbs

You're right, I had it bass-ackwards after 50 years. What Reuben was after was exposure control by flash duration. Not quite sure now what was the point. The abstract alludes to exposure control.

And I mis-remembered how to spell Wechsler :-(

Reading the summary: Discharge capacitor to a lower voltage before firing the tube controls light output.

My wife worked for Doc Edgerton while I was at MIT. His hallway was full of photos of undersea critters, with titles like, "Any idea what this is?" ...Jim Thompson

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My wife worked for Doc Edgerton while I was at MIT. His hallway was full of photos of undersea critters, with titles like, "Any idea what this is?"

...Jim Thompson