Archive for the ‘High speed photography’ Category

Triboluminescence of sugar and fractoluminescence of glass

Saturday, August 11th, 2012

A very simple but quite surprising experiment:

- take a sugar cube to a very dark room
- smash it with a hammer (which is not an easy task in the dark!)
- look at the sugar cube and see what happens

You should be able to see a clear blue flash “inside” the sugar cube.
Though the effect is clearly visible, taking a photo is quite hard.
I used a very light sensitive lense (f/1.8) and the camera at the most sensitive mode (ISO 3200) and the blue light was still in the lower part of the histogram:

Above: hammer and sugar cube in normal light, below the sugar cube in the dark while being smashed with the shutter open for 3 seconds at f/1.8 and at ISO3200. The room was not perfectly dark, so besides the blue glow, you can still see the vice and the remains of the cube.

The effect is called triboluminescence, an apperently not-so-well understood optical phenomenon that occurs when crystals are rubbed. So when you use more force/energy in hitting the sugar, you should get more light. Therfore shooting a sugar cube may give better photos:

Sugar cube shot from the side with an air pistol, indeed producing more blue light than when crushed with a hammer.

A sugar cube, shot from the direction of the camera. The triboluminescent light actually becomes a high speed flash itself. The dark spot is the pellet hitting the sugar.

I got to this subject, because a similar (though yellow) effect appeared in the mirror we shot with the .308 Winchester. However, when I smashed a piece of mirror with a hammer, no optical effect like in the sugar was visible at all. Some scientific papers seem to suggest that triboluminescence occurs in glass and that it has a Boltzmann like spectrum (similar to a glowing hot object). A more appropriate term may be fractoluminescnce in the case of glass: before it shatters, glass breaks at a very high speed, and the energy dissipated in a very small region of the material at the crack tip heats it up, and thermal photons are emitted (as confirmed by Elisabeth Bouchaud).

Light effect in the glass of a mirror. The fast flash has actually captured the bullet tip right before it impacted the mirror. The muzzle is in the center of the orange muzzle flash. The yellow light really seems to originate from the (cracks) in the mirror.

3D high speed photography

Thursday, August 9th, 2012

Flash photography lends itself perfectly for 3D photography: the flash ensures that the two photos that make up the anaglyph (stereo image) are taken at exactly the same moment in time. Simply place 2 cameras with the same focal length (preferably identical cameras with identical settings) and point them at the same scene.
By using a simple Matlab script, the red and green+blue channels are mixed to make a 3D image that must be viewed with red-cyan (or red-blue) glasses.
When you first make black and white images of the two photos, you can make a black and white anaglyp. For some situations this is the only solution: take for example the bright red tomato. You simply cannot expect that to work with red-blue glasses (nothing will pass the blue filter).

Chalk in 3D

Exploding orange about 4 milliseconds after impact. The bullet has long gone.

Same scene in black and white.

Tomato anaglyphs only work in black and white.

Ultra-high speed photography: .308 Winchester

Saturday, July 21st, 2012

Some photo’s taken of the .308 caliber (DPMS LR-308, 150 grain Full Metal Jacket) at a muzzle velocity of about 860 m/s (3100 km/hour or 2820 feet per second), roughly 2.5 times the speed of sound. The light source was a home grown air-gap flash, triggered with a simple piezo microphone.

.308 exiting the barrel, photographed via a mirror

The obligatory business card.

Lightbulb shattered by .308

Clear lamps are bullet proof.

.308 tumbling through chalk (backside of bullet towards camera)

Jus de tomate preparation .308

Jus d’orange a la .308

.308 round tumbling after passing through an apple

Note that vaporized tomato, orange and apple juice all are white instead of red, orange and green!

Phosphorescence of quartz

Friday, May 25th, 2012

The inner glass tube of the air-gap flash so far was made of Pyrex. The spark has a temperature of about 30,000 degrees Celsius, so the flash gives the pyrex a horrible temperature shock (more than 30,000,000,000 degrees Celcius per second). Pyrex is a good choice, since it has a very low thermal expansion coefficient, causing a minimum of stress in the material when heating up. For the same reason Pyrex is also very popular in kitchens (glass that does not break in an oven) and telecopes (mirrors that need to keep their shape extremely accurately at a range of temperatures, for the Hale telescope they even tried quartz, but gave up and used Pyrex).

Still, after a random number of flashes the Pyrex tube tends to shatter to small pieces.
In comes quartz: it has an even lower thermal expansion coefficient (4e-7 m/mK, about four times lower than that of Pyrex).

To my surprise the quartz tube has a beautiful blue afterglow for several minutes, which reminds me of Cherenkov radiation as seen in nuclear reactors. After some searching I found it is blue phosphorescence, caused by impurities in the quartz, cuased by the UV in the spark. It shows nicely how the spark went over the surface (different every flash).

Upper half shows the flash tube, with the inner tube being made of quartz. The lower half shows the phosphorescence that lasts several minutes after the flash.

Party time

Tuesday, April 3rd, 2012

Bet you never took the time to look at this happening!

Cork leaves the bottle at about 70 km/h.

Here is a 100% crop of the bubbles.

Click to see 100% crop.

“DNA” of an air-gap flash: spectroscopy

Saturday, March 31st, 2012

The color of a light source can be unravelled into it’s principal components using a diffraction grating.
Each separate color (wavelength) is bent to a different position, resulting in a rainbow like image.
To best separate each color, a photo is taken of the light source behind a narrow slit. The resulting spectrum is an infite numbers of copies of that slit, spread out into a spectrum.

Setup, showing the slit below, with the spark gap behind it and the diffraction spectrum floating above in air

A Cokin P040 diffraction grating (240 lines per mm) was simply placed in front of a DSLR lense (5 Euros only, I was lucky, 40 Euros is a typical price), resulting in the following image:

Spectrum of the air-gap flash

Since air consists of 80% Nitrogen, 20% Oxygen and a small fraction of Argon, it’s spectrum should be a mix of the spectra of these atoms (some simulated spectra here). But when I look at this spectrum, I find it hard to match them. Also it lacks any hint of yellow tones, to me it is just RG&B.

For comparison I have also imaged my Nikon SB-600. I would expect a spectrum similar to Xenon, but also that does not really look like it.

Nikon SB-600 spectrum

For reference, these are the spectra from Joachim Koppen’s website (

Nitrogen spectrum (78% of air)

Oxygen spectrum (21% of air)

Argon (1% of air)

Finally an attempt to match the spectra of the air-gap flash to Oxygen and Nitrogen. It seems that the spectrum mainly consists of Nitrogen (which was to be expected). The simulated spectra of Oxygen en Nitrogen were blurred to match the resolution of the grating/slit photo.

Spectra of Oxygen and Nitrogen (simulated) together with the grating result for the air-gap flash.

Flash close-up

Saturday, December 10th, 2011

I wanted to see what the flash produces before and during the flash.
While waiting for the trigger the cathode and anode produce a lot of corona and corresponding ultraviolet light.
During the flash a spectrum of oxygen and nitrogen is produced and it seems some copper (green) as well.
The spark also contains a lot of infrared radiation, which causes the red tail in the highlights of some fast moving objects. To my surprise the trace of the spark was very different each flash. It seems Edgerton cut a groove in the inner glass tube to guide the spark.

The gap has 20.000 Volts and a capacitor of 0.05 micro Farads. That equals an energy of 0.5*C*V^2=10 Joules. Since all of that energy is released in about 0.5 microseconds, this means a the flash has a peak power of 20 MegaWatts. Imagine twenty thousand floodlights of 1000 Watts, all illuminating a gap of 20 mm…. That also gives an impression how incredibly short half a microsecond is.

Microsecond air-gap flash photography

Sunday, October 2nd, 2011

To take photo’s of really fast events, you need a very short duration flash. A normal camera flash lasts about 1-3 milliseconds at full power. These pictures were taken using a home built microsecond flash, a thousand times faster.
Example: a bullet travels at 1000 feet per second (305 m/s), so in 1 millisecond it would be blurred out to a 1 feet (305 mm) long blur. Using a microsecond flash, the blur would be 1/1000 of a feet or 0.3 mm.

This card deck is incomplete now (AR15, 9mm bullet)

No flames like .44 magnum flames

Bullet just left the S&W 686 .38 Special at about a 1000 feet per second.

A classic: 1911 makes for a messy shot

Microflash has more "stopping power" than a hollowpoint. Measured at 329 m/s or 1184 km/h using a chronometer. It rotates at 80120 RPM, once ever 9.7 inch.

Small balloon collapses very fast, even compared to bullet speed.

Chronometer showing 9mm hollowpoint speed in m/s (1080 fps).

Another balloon hit.

.177 pellet exiting the muzzle of an air pistol

Soap bubble hit by pellet

The air-gap flash was built from readily available scavenged and new electronic components, very similar to the EG&G MicroFlash 549.
The flash was triggered by an Arduino microprocessor with user selectable delay of about 1 millisecond using a piezo microphone to detect the shot.
Main inspiration/information for (and warning against) building a similar flash unit can be found here.

Complete flash system with tubular flash housing, Arduino in a control box and microphone.

Flash stripped from drain tube showing from left to right: spark gap, capacitor, trigger bobbin, trigger circuit and flyback driver.

Business end of the flash

Close-up of the 20mm spark gap and trigger wire.