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.
Party time
April 3rd, 2012“DNA” of an air-gap flash: spectroscopy
March 31st, 2012The 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 (http://astro.u-strasbg.fr/~koppen/).
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
December 10th, 2011I 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 flash photography
October 2nd, 2011To 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 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.
The 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.
Arduino triggered lightning photography
June 28th, 2011Ingredients:
- Arduino
- a simple photodiode
- a cheap shutter release remote cord from Ebay to get a plug for the Nikon D90 remote port (2.60$)
- a major thunderstorm after sunset
Procedure:
- DSLR set to manual 1s exposure time, diaphragm wide open , ISO low
- Arduino waits for light flash detected by phototransistor
- On the detected light flash the port connected to the remote cord goes LOW
- Shutter opens after 69 ms (that is the Nikon D90 shutter lag)
- since lightning is not an instantaneous event you still catch the final discharge and/or afterglow
Bahtinov Grabber goes 64 bit (and 32 bit update)
June 23rd, 2011This is the introduction of a 64 bit release of the grabber. Download Bahtinov Grabber 64 bit (834) here.
It was tested in combination with ASCOM 5.5b. Make sure you have that installed.
This same release is available in 32 bit as well: download Bahtinov Grabber 32 bit (1048) here.
Main changes:
- generic, more accurate calculation of focus error. Also works for masks other than the standard 20 degrees
- choice which R,G,B channel(s) should be part of the line detection
- audible feedback
Polar alignment check using a single plate solve
October 31st, 2010This is how:
- set up your mount
- point telescope or camera towards Polaris
- take long (30s?) exposure of which the first 10s are static and the last 20s rotating the RA axis for 180 degrees
This results in an image that both show a star pattern and a set of circles.
By “plate solving” (finding the celestial coordinates) of the star pattern and drawing a RA, DEC grid you can see how much your polar alignment is off. Perfect polar alignment will result in concentric star trails and RA DEC grid.
Plate solving can be done with astrometry.net.
RegistaC#
September 22nd, 2009Yet another non-rigid registration and stacking tool.
This time using the “demons” technique for non-rigid registration (matching) of AVI frames.
I hope the enforced workflow makes the use of the software clear by itself:
download: RegistaC# (474)
.NET 2.0 required if not already installed
The application was entirely written in C# (VS2005 express), making use of the FFTW library for FFT (wavelet filtering and global shift detection) and the AVI library from Codeproject.
The idea is
1. open avi and select a nice frame
2. align all other frames to that frame
3. measure quality of all aligned frames in preferred region of interest
3. average best X% frames
4. correct all sharp frames for seeing using “demons”
5. stack again for final result
6. apply wavelet sharpening
after that you can re-iterate alignment, seeing correction, frame selection etc. quite ad-lib.
Here is an explanation of the demons technique: demons powerpoint
feedback more than welcome!
3D images from 2D
September 14th, 2009You can turn a simple 2D image of a planet or the moon into a “3D” image using this 3Dfication.
Make sure you make square crop that fits the planet or moon with only a small margin, of the image you want to use for 3Dfication. Using animation, you can make movies like this and this. AVI’s need the DivX codec.
download: 3Dfication (596)
Periodic error and Polar alignment error model
September 8th, 2009Using linear algebra, a model for calculating the trails that stars produce when making astrophotos from an equatorial mount was created.
An ideal mount that is perfectly parallel to earth rotation axis results in photo’s with pinpoint stars.
In the real world, the stars will always produce trails. Main causes are
- imperfect polar alignment
- periodic error of the (worm) drive
- RA drive rate that is different for siderial rate
Download Star Trails (615) here.
All of these parameters can be played with in this model.
What I learned from the simulations:
For DEC=0 and a small polar alignment errors, the stars will describe a vertical line over 24h:
For DEC>0 and a small polar alignment errors, the stars will describe an ellipse, over 24h. The ellipse will be wider for larger DEC:
The periodic error will always add a wiggle in RA to the curve:
