High Speed Air-gap Flash

A bullet hitting a solid brass rod.

If you just want to buy an assembled and tested airgap flash, I have made an updated versions that can be purchased at Information Unlimited.

In my quest to capture amazing high speed photographs I notice that when photographing shooting bullets the bullets were blurred. I found that standard xenon tube, which standard flashes use, is very bright for the energy put into it because of glowing xenon gas. The book Electronic Flash Strobe by Harold Edgerton explains all the calculations, but in practice this means all the flashes from Nikon, Canon and others that use xenon flash tubes have a minimum duration of 1/40,000th of a second. That’s fast enough for most things, but not for a shooting bullet travels around 1000 feet/second. In 1/40,000th of a second that bullet can travel about 1/3rd of an inch leading to blurry photographs of bullets.

To solve this I had to make a faster flash. I’m certainly not the first to do this. I think that was Harold Edgerton. He actually created a company called EG&G to sell a product called the 549 Microflash, but that company has been dissolved and the product discontinued. Sometimes you can still find these flash units on ebay, but the ones I saw were selling for $8K+. There is also a company called Prism Science Works making a modern version of these for researchers, but you’ll need really deep pockets to afford one of those. I saw directions on how to build one in the August 1974 issue of Scientific America and emailed Alan who had already built a few. After this research I realized I could build a sub-microsecond flash for just a few hundred dollars. A sub-microsecond flash means the flash duration is less than 1/1,000,000th of a second or about 25 times faster than a xenon flash.

Here is an image showing how an air-gap flash compares to a standard flash when photographing a 1000 feet/sec pellet.

I am a strong believer in sharing knowledge so I’ll explain how I made my air-gap flash, but I am knowledgeable with high voltage safety procedures. You should not build this because this flash will kill you. It really will. This flash requires charging a 35,000 volt capacitor that will easily kill a person for a single mistake. I have a safety checklist that I use ever time I plug in this flash and it still scares me. If it didn’t scare me then I shouldn’t be using it because this thing is dangerous. The below information is for educational purposes only. Do not build one! If you go against my advice and do build one, I am not responsible for any injury, death, or any other problems it causes.

Here is a list of the main parts I used to build my air-gap flash:

Here is an overall diagram of how all the parts fit together.

This is the schematic for the custom circuit board I made. Basically it doubles the 120V AC and uses an external signal to trigger the 45 kV transformer.

And here is a picture of my custom circuit board.

Here is a picture of the air-gap flash.

This shows what is plugged into the air-gap flash. 120V to run the 45K trigger transformer, 14V to charge the big capacitor, and a 3.5mm cable to use for triggering.

Here is a side view. Notice that the reflector has a thin sheet of Plexiglas over it to make cleanup easier. The metal reflector is also grounded in case the plexiglass tubes shatter, and they do shatter sometimes. I have found they last longer if I use latex gloves so no oils from my hands get on the glass tubes.

This is a close up of the glass tubes where the spark happens. The outer glass tube is just for protection and to reduce noise. The inner tube has the wire 45 kV trigger transformer inside. When that transformer is triggered the air ionizes and that cases the big capacitor to discharge in a 1.5 inch spark that creates the flash of light. To seal the inner tube I melt one end with a torch until it is sealed.

A top down view that shows how everything is connected.

This rod is very important. It is how I discharge the big capacitor after every use so I don’t die when I’m working on the flash.

Those extra wires and circles are there so I had an easy way to discharge the capacitor.

Note about using it with the Camera Axe. The Camera Axe only allows a trigger voltage of up to 20V. This has a trigger voltage of 240V so I needed to to put a high voltage protection circuit between this and the Camera Axe. There are many examples of these circuits on the web.

Here are a few results:

Glass rods being hit by a bullet.

A balloon being hit by a bullet.

Thanks Alan for your help and letting me use some of your amazing photos.

57 Comments

  1. Tom Hargrave said,

    January 10, 2011 @ 2:57 pm

    Reminds me of the primary side of a Tesla coil I built years ago. The differences are my Tesla coil used a neon sign transformer as the power source, a glass plate capacitor and a adjustable spark gap. The spark gap ran continuos and it generated the RF frequency needed to drive the RF transformer. The primary side of the RF transformer was a single spaced 6 turn winding on a oatmeal can and the secondary of the RF transformer was a tight single winding of varnished wire on a paper towel tube.

    My Tesla coil would brightly light a 40 watt florescent light held 6″ away!

    High voltage projects are fun, but they are dangerous if not handled properly. But so is 110 VAC.

  2. Matt said,

    January 10, 2011 @ 4:06 pm

    Great project here, I love high speed photography like this.

    One suggestion to make the project safer is to install bleeder resistors directly across the capacitor output so that when power is removed the capacitor is discharge by default. The manual discharge technique is probably the most dangerous part of this project. A resistor voltage divider to a battery powered panel-mount voltmeter (or just a high voltage voltmeter if you have one) would also be a nice safety option, or you could rig something up with neon indicator lamps.

  3. Wade said,

    January 10, 2011 @ 5:18 pm

    Hey, great article. What’s the red sphere in the first photograph of the bullet hitting the brass rod?

  4. Ralph said,

    January 10, 2011 @ 7:13 pm

    tres’ cool
    built flashes timing circuits for flashes & even water drops are blurred in at a macro level at 1/40000
    but this is definitely on the must try level ..
    have you measured/calculated the output ? (GN ?)

    BTW: a good reference is “Engineering and Scientific High Speed Photography”, W.G.Hyzer, Pub.1962

  5. Maurice Ribble said,

    January 10, 2011 @ 7:36 pm

    Matt, the capacitor has a fair amount of leakage so it does discharge over an hour, but speeding that up with a resistor is good idea. I do have a high voltage voltmeter that I used for debugging the circuit and I thought about doing a voltage divider to read the voltage. I decided that by keeping it simple would be the safest way for me, but I can see where a few things like that might be useful.

    Wade, the red sphere is actually a plastic tip to the pellet that was used. The pellet was fired backwards so that red tip was in the back.

    Ralph, I’ve done a lot of water drop photography and have never noticed blurring with a standard flash. You might want to double check that your flash is working fine. I did have a damaged flash once that did show blurring on water drops.

    Ralph, I haven’t measured the output, but it’s pretty close to my Canon 580 EXII at 1/64th power. Thanks for the book suggestion. I might check it out someday.

  6. Sohrab said,

    January 11, 2011 @ 4:54 am

    What kind of motion sensor do you use to trigger the camera and flash ?

  7. Maurice Ribble said,

    January 11, 2011 @ 5:19 am

    Sohrad, I use the Camera Axe http://www.CameraAxe.com for high speed photography. It has all sorts of different sensors for different use cases. All of the photos above were a bullet and used the projectile sensor. Here is a posting about this sensor: http://diyphotography.net/bullet-photography-at-home

  8. vespine said,

    January 11, 2011 @ 6:33 am

    hey, could you take a photo of the flash going off? with a dark filter or something to capture the spark? I wonder what that would look like :)

  9. BulletProof said,

    January 11, 2011 @ 3:20 pm

    Why does the article call the projectiles bullets, when they are pellets?

  10. Al said,

    January 11, 2011 @ 7:39 pm

    Very nice article. What is the recycle time?

  11. alan sailer said,

    January 11, 2011 @ 7:56 pm

    BulletProof;

    bul·let (blt)
    n.
    1.
    a. A usually metal projectile in the shape of a pointed cylinder or a ball that is expelled from a firearm, especially a rifle or handgun.

  12. Maurice Ribble said,

    January 11, 2011 @ 8:26 pm

    Good question Al. The recycle time for a full charge is something under 5 seconds. If I accidentally have it so that it continuously fires it fires in about 2 seconds, but that isn’t a full power flash.

  13. VEC7OR said,

    January 12, 2011 @ 5:11 pm

    Awesome, didn’t knew you even have those.
    Can you use LED’s for that purpose ? They are nanosecond fast, but I guess the output is just too small for the time needed to record something.

  14. Maurice Ribble said,

    January 12, 2011 @ 5:59 pm

    That’s a good point about LEDs being fast enough, but as you guessed they don’t output enough light. I did some calculations about 6 months ago and with 100 1W LEDs the output was a few orders of magnitude lower than this flash.

  15. TK said,

    January 12, 2011 @ 7:21 pm

    Just reading around about the alternative method, which would be to get a faster shutter ie external shutter sitting infront of the lens, it appears that the delay time in the camera is the mirrors and not the shutter, which operates in the range of 4ms. So I see why you didn’t go that way. As for LED’s, I have a pannel of 12 by 40 1/4W LED’s, I use on a lantern battery, this was bright enough to be blinding at 1m, and noticeable at 1km away, and this panel was totally unfocused. Bought the LED’s cheap from here http://www.hebeiltd.com.cn/

  16. Ralph said,

    January 13, 2011 @ 8:10 pm

    RE blur of a waterdrop

    I believe most of my blur is caused by the tail of the flash ..T.1 is very short T.5 is short but T.95 is getting up there ..

    Question about your setup : id your 25Kv supply positive or neg (or did you care ?)
    (parts are ordered ‘ecept the “Cap” .. have to look for cheaper one .. )

  17. alan sailer said,

    January 14, 2011 @ 12:02 pm

    Ralph,

    Be careful on buying a cheaper cap. The cap required must be fairly low inductance and usable for pulse operation. The second requirement is the most important.

    Out of five different types of capacitor I have bought off of Ebay to try as microsecond flash caps, only two worked. The Maxwell is the best, doorknob caps also appear to work.

    The other three failed quickly in use. When the capacitor fires the flash, it is nearly a direct short. The peak currents are huge, so if the capacitor is not designed as a pulse cap, the plate material inside the cap will erode and destroy the cap.

    The polarity is only important in that it is a good idea to ground the negative. terminal.

    It is also a very good idea to run that ground to the metal reflector. The flash lamp is glass, it can and does break, leaving the possibility of an arc from that deadly cap to the reflector. If you touch that ungrounded reflector, you touch that cap and then you can’t take any more pictures.

    Ever.

  18. AV said,

    January 14, 2011 @ 12:32 pm

    can you pl share your safety checklist ?

  19. Bayley said,

    January 16, 2011 @ 8:17 pm

    @Ralph
    In regards to capacitors, I believe they have to be pulse-rated capacitors to work. High-voltage DC filter caps can (and most likely will) fail, sometimes catastrophically.
    The white plastic Maxwells work. So do the metal canned PULSE (not filter) capacitors made by Maxwell, Aerovox, Condenser Products, and Plastic Capacitors.
    You can often recognize a pulse capacitor by its terminals – they are usually very thick in order to handle the high currents.

  20. Joseph S. Wisniewski said,

    January 17, 2011 @ 4:31 pm

    I thought the comment about power being about equal to a speedlight on 1/64 power to be a bit confusing. A speedlight is about 60J, so 1/64 power is about 1J. You’ve got 9J in that cap (1/2*25kV^2*0.03uF).

    Is an air gap flash that inefficient compared to xenon?

    No bleeder resistors?

    A little voice is whispering to me: scam the trigger power supply from a cheap flash, run everything of 10 NiMH cells, put the reflector inside the plexi box, and nothing goes through the box walls but optical trigger and control signals. ;)

  21. Ralph said,

    January 17, 2011 @ 7:03 pm

    Yes / seen some of the other cap types & know enough to stay away from them ..
    (used to sell electronic components in the 70′s .. )
    seen on similar to wht you are using for ~115$ may go that route …

    & ‘kindof ‘ yes to Joseph S. Wisniewski : optical separation is the best way to trigger, but to much hassle in a old flash … think i’ve got one kicking around my junk … have to go digging ;)

  22. Maurice Ribble said,

    January 17, 2011 @ 10:17 pm

    Xenon is used for various reasons including the fact that it improves efficiency. I didn’t do efficiency calculations and am just stating what I measured.

    There is no bleeder resistor, but caps like this are naturally leaky. Mine drains in about 15 minutes.

    A cheap flash works at about 200V so you will have problems bumping that to 20KV since it probably wouldn’t charge the cap as fast as it’s natural decay discharge rate.

  23. Fred said,

    January 18, 2011 @ 11:50 am

    Does it automatically start recharging again after you fire the flash like a regular flash?

    When the flash discharges does the capacitor discharge to empty?

  24. James Bennett said,

    January 18, 2011 @ 8:10 pm

    That’s awesome work. My first job out of school (22 years ago) was working for a company making exactly these kind of flash units for the MOD and research organisations. I did a quick google for the company and they still seem to be going today.

    http://www.pulsephotonics.com/gallery.htm

    It was at the same time one of the most boring jobs ever (spent a lot of time with not much work to do) and the best job I’ve ever had. I learnt a lot, not least how to fire an air rifle accurately to test high speed flash and digital camera units.

    We used to build the 16kv HT charge capacitor units in house from a set of three pulse capacitors, some diodes and lots of epoxy. Testing those was fun some days. One Monday morning I found myself on the other side of the room, that’s a mistake you don’t make twice and it gave me a healthy respect for high capacity capacitors.

  25. A not-so-famous writer said,

    January 21, 2011 @ 6:46 pm

    Those extra wires and circles are there so I had an easy way to discard the capacitor.

    Don’t you mean “discharge” not “discard”?

    EZ

  26. Maurice Ribble said,

    January 21, 2011 @ 7:17 pm

    AV, I’ll try to type out the checklist sometime since it’s hand written right now. But I want to emphasizes that I don’t think people should be building this especially if they want a safety list given to them.

    Fred, yes it does automatically recharge and it mostly discharges, but not enough to stop being lethal.

    Thanks for the discard/discharge bug. I fixed that.

  27. Walther Grube said,

    January 23, 2011 @ 9:59 am

    Wow! Just what I need to make my pictures less blurry! he he
    Jokes aside, great job! Well explained.

  28. Marsel said,

    February 7, 2011 @ 2:27 am

    would this one be suitable for PULSE usage of this project ?

    http://cgi.ebay.com/40kV-25nF-High-Voltage-Polystyrene-capacitor-HAM-audio-/360303200204

    Thanks!

  29. dave-o said,

    February 18, 2011 @ 6:11 pm

    One hint I gathered from reading a lot of Edgerton’s stuff about air flash, is that the center tube should be made of quartz, not borosilicate glass. Mostly it’s so it can handle the heat of the arc on it’s surface, but also because, apparently, the quartz tube acts to quench the arc after excitation is turned off, reducing the red trail. I’m trying to source some for my own version now, along with the capacitors to literally copy the 549 design (with modern control for duration and trigger). It’s tough to find in less than large quantities though, and closing the end without compromising the tube itself appears to be something of a hurdle.

  30. alan sailer said,

    February 24, 2011 @ 6:20 pm

    Dave-o,

    I would like to add to your comments with a few observations on the quartz vs borosilicate glass.

    I’ve run an estimated 10,000 flashes on a air flash and have used both quartz and borosilicate glass. Both break about as often. Sometimes a tube will last for only a few flashes, other times it will last for hundreds.

    Both quartz and borosilicate have a significant long red tail to the flash, I don’t know which is better.

    Edgertons tube was thick walled with a groove cut in it, apparently to guide the spark. Another air flash builder named Jasper Nance says that her tube, a thick walled quartz tube is very long lived, so maybe you need quartz and thick.

    So based on my own experience, its not really worth it to get quartz over borosilicate from a performance point of view. From a longevity point of view, thick walled quartz may be better.

    Have fun. I always thought he original 549 using the storage cap as the doubling cap was a clever idea. That Plastic Capacitor unit is expensive, though.

    Cheers

  31. michael leach said,

    March 31, 2011 @ 6:40 am

    Amazing pictures. High speed photography is an area I’ve been exploring for several years, only for wildlife subjects. The high-speed flash unit I’ve been using was put together by a company that has now gone bust. It is now playing up and needs someone who knows what they’re doing to look at it. Is there any tech expert out there who knows anything about flash technology ? And who would be interested in trying to track down the problem ? I would be very happy to pay for their time.

  32. dan said,

    April 9, 2011 @ 5:08 pm

    Hi I actually have one of these EG&G Microflash 549 units in perfect condion with very light use. if any one if any one is intrested. send me an offer to dak_electronics@yahoo.com.

  33. Chris said,

    June 4, 2011 @ 10:07 pm

    LEDs have potentially very short (~nsec, as noted above) flash duration, but white LEDs are actually blue LEDs with a dab of “phosphor” over the light emitting region of the LED. The phosphor is excited by the blue light from the LED into emitting a spectrum of light which looks white to the eye. I haven’t found any information on the flash duration of white LEDs so I suspect the “tail” is quite long, due to persistence in the phosphor. I haven’t had a chance to build a circuit to test the flash duration of LEDs. One suggestion for anyone who’s thinking about building such a circuit: the light pulse turnoff time should be shortened if the LED is reverse biased to speed up sweeping the electrons and holes out of its active region. This suggests driving the LED with a pulse transformer, which, in the right circuit, will reverse bias the LED when the current in the transformer primary is turned off.

  34. Jim Bales said,

    June 15, 2011 @ 3:54 pm

    Maurice — very well done!

    I have started using the Camera Axe in teaching Edgerton’s Strobe Project Lab subject here at MIT and have found it to be a great help.

    FYI, the Prism Science Works SPOT flash unit is less expensive than an EG&G Microflash. I *believe* Bob Root at Prism has them priced around $3,000 to $3,500 each.

    Best,
    Jim Bales
    MIT Edgerton Center

  35. alan sailer said,

    June 22, 2011 @ 4:48 pm

    Chris,

    This is not the last word on the subject, but a few months ago I did a quick test of a phosphor type white LED, a Cree XLamp. I just used a MOSFET wired up to a pulse generator, nothing fancy. I got a 2usec pulse with reasonable rise/fall times, no signs of any red trails.

    I was using the same detector which easily shows the trail of my air gap flash.

    The basic problem with LEDs is intensity. The air gap flash is millions of candlepower. Getting there with LEDs is not for the faint of heart. I know for sure that you won’t have either a line or point source of comparable intensity using LEDs.

    Microsecond microscopy anyone?

    Jim,

    Thanks for the SPOT price. It was one of those things I have wanted to know, but never got around to.

    Finally another small data point on the quartz tube issue. Several months ago I (again) up-dated my flash tube to use some commercially sealed quartz tubes I had lying around.

    The result is no failures.

    I don’t know why this is, but it is great not having to rework my flash tube every few weeks.

    All I can think of is that the commercial tubes are properly annealed, although I didn’t think quartz needed annealing.

  36. sean said,

    June 24, 2011 @ 9:35 pm

    fantastic.
    of course, being inquisitive and stupid (in a smart way), i have a question. i am doing high speed collision research on hollow metal boxes using a pneumatic machine, filming them with old 16mm high speed cine cameras. art, i call it. i have just started to think of making a drum camera for 2,000 – 4,000 frames per second captures (only 100 total frames or so, so very short in real time). Do you know of anyone who has played with air-gap sparks in this sort of repetition range? Lucien Bull, technician for Marey, made his own, filming dragonfly wing beats on his home-made stereoscopic drum camera, in 1904, so it is possible.
    Its really hard trying to find any info, and I am unwilling to fork out the horrendous megabucks for commercial high repeat strobes, so just asking in case…. Air gap? multi multi multi led array? i am a maker, lathe, tig, etc etc….
    Thanks,
    Sean.

  37. Randy said,

    November 4, 2011 @ 10:57 am

    fire·arm
       [fahyuhr-ahrm]
    noun
    a small arms weapon, as a rifle or pistol, from which a projectile is fired by gunpowder.
    Are your “bullets” propelled by compressed air or gunpowder???

  38. Maurice Ribble said,

    November 4, 2011 @ 11:02 am

    Most people use air-powered rifles. That’s what I’ve been using, but I did recently find a person with a firearms that would allow me to photograph them. Still need to take him up on the offer sometime.

  39. Tony said,

    December 2, 2011 @ 7:35 pm

    Hi,
    Is that an HV-250 you’re using OR an HV-25??

    Thanks for your help.
    TR.

  40. Dave said,

    December 16, 2011 @ 4:12 pm

    Hi,
    I have a bit of a problem with your trigger circuit. If you inadvertently hook up the hot and neutral legs of the 120Vac backwards and then connect the trigger circuit to your camera the camera will be HOT. The same can be said for any sort of external trigger module you connect to your trigger circuit. Why not put in an isolation transformer on the 120Vac and then tie the circuit ground to Earth (safety ground in the power cord)?

    There are plenty of ways to fry yourself playing with these circuits. Why not eliminate the hazards where you can?

    Additionally, if the trigger cable (3.5mm plug) is connected to a modern DSLR it is likely that the external trigger circuit in the DSLR will burn out because it is designed to work with roughly 5V versus the switches in old cameras which are rated for a couple of hundred volts. Since you already have the 14V wall wart you can add the necessary circuity to convert your trigger from a high voltage trigger to a low voltage trigger without much effort. That will simplify the requirements for any external trigger devices (cameras, LED interrupter, sonic, etc).
    Dave

  41. Bernie said,

    December 24, 2011 @ 9:27 am

    I was thinking about making a safer, lower voltage version of this using a 600v 0.03 uF capacitor with a 1/3 mm spark gap… Do you think this would work?

  42. Maurice Ribble said,

    December 24, 2011 @ 11:49 am

    I talked with Alan about this and he pointed out that the energy in a capacitor decreases with the square of voltage. This means 600V would give about 400 times less light. This isn’t bright enough my use cases.

  43. MuratC said,

    December 26, 2011 @ 4:08 am

    600v cap with 1/3mm spark gap willl be totally useless try. We beg for more light even with a 35kV cap and a 30mm gap flash

  44. Douglas Blissard said,

    February 9, 2012 @ 1:34 pm

    Great subject with lots of great comments. A couple of thoughts and questions.
    1. Why not use pointed electrodes so the spark is not in contact with the quarts or glass surface? It occurred to me that the long red tail might be black body radiation from the superheated glass or quartz and the electrode tips.

    2. Does anyone have a spectra of the output to determine the max output wavelength. I was thinking it might be possible to tweak the spark to make the output optimal in the visible wavelengths a lot of energy could be going into the infra red and/or UV. Shielding the output of the electrode tips might prove useful in getting rid of the

    3. How does the spark length or gap affect the output? It seems with Xenon flash tubes bigger = brighter. How big can you make the gap?

    4, Could you substitute a commercial type bulb like http://www.msscientific.de/xenon_lamps.htm assuming the bulb is compatible with the power and voltage of your system?

    I look forward to thoughts and comments.

  45. alan Sailer said,

    February 13, 2012 @ 2:19 pm

    Douglas,

    1) The arc is supposed to stay in contact with the quartz. It cools the plasma faster, makes the spark longer and thus higher impedance (less ringing, shorter pulse of light).

    2) I have seen some spectra published, but didn’t get any information from them. The flash is UV rich, judging from the fact that I can get fluorescent dyes to glow well.

    3) Longer gaps need higher voltage and do give higher output. It gets more and more difficult to make a corona free flash at higher voltages.

    4) Why would you want to do this? The whole point of using an air gap/guided spark flash is to get a short duration spark. Unless you go to heroic lengths, it is not possible to get short duration flashes with xenon.

    Finally, the red tail is barely noticeable in most photographs. Other than a technical exercise, why go to great lengths to fix the problem?

    Cheers.

  46. Stuart Hirth said,

    March 16, 2012 @ 5:56 am

    Thanks for posting design info and pictures. Really not happy with your discharge stick. Got bitten by the second last stage of a 30kw transmitter once. When I came to, I was on the other side of the room. A few things you can do 1) wire in to the box a Voltmeter so you know the thing is discharged. 2) as a backup to the first, pop in a neon indicator (with appropriate resistance) and 3) throw away your discharge stick and discharge through a suitable resistor. Alan is spot on, there is much energy wasted in UV. Am currently looking at ultra fast LED flash designs, anyone got any good ccts?

  47. Stuart Hirth said,

    March 16, 2012 @ 6:49 am

    Hey Matt, just read your post at the top. You already concluded same, didn’t plagiarize, just didn’t read.

  48. Prof. Greg Parker said,

    May 5, 2012 @ 6:34 am

    Very, very impressive indeed – and I am not easily impressed :) You have done some great work here. I have spent 30 years down the Xenon route which is capable of giving sub 10-microsecond pulses at 50 Joules but you need to use a Xenon/Nitrogen mix to cut down the afterglow tail (which also reduces the light conversion efficiency of course). For true microsecond work the air-spark seems to be the only way to go, it’s just a shame the electrical to optical coversion efficiency is so poor (compared to Xenon).

  49. Bart said,

    May 11, 2013 @ 7:01 am

    I am by no means an electronics expert, so I would like your opinion on this:
    Could a marx generator be used to archieve the same effect as this air gap flash?
    This would save me the money for the pulse capacitor…

  50. Maurice Ribble said,

    May 12, 2013 @ 6:15 am

    Bart, the main reason that wouldn’t work is there is not enough energy to generate enough light. A secondary problem is you’d need to devise a way to create a spark withing 1 microsecond of when you want it.

  51. Paul said,

    May 19, 2013 @ 1:45 am

    Hey Maurice,

    Brilliant work mate. So your 35kv cap is only charged to 25kv? I have a 50kv 0.01uf cap, do you think this will function in your design with 1/3rd capacitance? what if I extend the V multiplier
    to provide 50kv @ 0.01uf? What differences should I expect in light output?

  52. Maurice Ribble said,

    May 19, 2013 @ 6:07 am

    Correct, the 35kv cap is only charged to 25kv. If you 50kv cap is rated for pulse discharges (most caps are not) it will work fine at 25 kv and generate the same light.

  53. Heron said,

    May 30, 2013 @ 12:58 pm

    Hey Maurice,

    Very good work. I want ask you about the marx generator, Bart ask you about that, and you said that wouldn’t work is there is not enough energy to generate enough light. A discharge time of capacitors is proportional to capacitance, means that we need a very low capacitance to have a very fast discharge, but, reducing a capacitance we also reduce discharge energy, and the light. The discharge energy is calculated E= (C.V²)/2, so, to compensate a low capacitance and reach a good energy level to have enough light, we need to increase the voltage. Because this, high speed flashes uses a high voltage discharge. Marx generator charge the capacitors in parallel and discharge in series, if we use a marx generator with 10 capacitors 10KV 0,04uF, a discharge will be equivalent to a capacitor 100KV 0,004uF, resulting in almost 8 times faster discharge and 10% more energy, comparing with your capacitor 35KV 0,03uF, also, we can use a lower voltage supply and cheap capacitors. Seems to me that a marx generator is the best option. I really not an expert and maybe I misunderstood something, can you help me? I used this online calculator (http://www.digikey.com/Web%20Export/Supplier%20Content/tt-electronics-welwyn-985/docs/tt-electronics-capacitor-discharge-calculator.xls?redirected=1). Thank you.

  54. Gavin Melville said,

    October 5, 2013 @ 3:05 pm

    I’ve got most of the bits together for an air gap flash, and I had had trouble finding an inner tube. Currently I’m trying the tube off a 1500 watt 8 in long halogen light bulb, about 5/16 in diameter, quartz and I’ve cut the ends off. This is the big version of the work light bulbs so common in hardware stores. I’m having trouble getting it hot enough to close the end off. From poking around on the net you need a hydrogen flame to melt quartz – has anyone had any success closing quartz?

    The other issue I’ve got is that I’m testing at about 1 joule, 35 kv and the arc is not hugging the tube, it seems to be slightly above the surface. Is the solution to make the discharge spiral slightly ie try to go through the tube?

    Regards,
    Gavin.

  55. Maurice Ribble said,

    October 5, 2013 @ 4:05 pm

    I’ve found these tubes work better as an inner tube than what I used here. When you melt the ends like I recommended here the inner tube tends to shatter after some use. These tubes work much better. http://www.lcmlab.com/13x100mm_Pyrex_Glass_Test_Tubes_p/206-0002w.htm

  56. Gavin Melville said,

    October 6, 2013 @ 12:24 am

    Thanks Maurice,

    I’d been thinking of Pyrex test tubes, but wondered if I was running out of room inside the bigger tube. I’ll try this first. Any thoughts on making the arc hug the tube?

    Regards,
    Gavin.

  57. Maurice Ribble said,

    October 6, 2013 @ 4:57 am

    I have not had any issues with having the arc hug the tube. One thing that seems different is you are running at 35kv, but I only run at 20kv.

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