Discussions (57)

Air-gap spark, anyone?

view profile

MarkRebuck says:

I'm at the point where my timing and triggering systems are effective enough that I can capture just about any event I want, but for good ballistics work, I need to do something about my flash system.

I started doing HSP by using a Vivitar 283 with the thyristor removed and shorted, but that only gets me down to about 1/10,000th of a second. I built my own Xenon-tube-based flash unit to get me a *slightly* shorter duration, but I think I'm close to the limit of what I can get with tubes.

So the next step is to do an air-gap spark. I can't see any other way to get the short durations I need. Unfortunately, documentation on building a good air-gap spark is a bit hard to find. Resources such as web.abo.fi/~joheriks/hispeed/howto.html give me good ideas, but don't quite complete the picture.

Have any of you built your own air-gap spark? If so, could you offer any pointers for problems areas? While the design of a spark gap is easy enough in theory, I don't want to mess up when I'm dealing with 20KV instead of the 300-400V for a normal flash.

Thanks!
1:24PM, 27 March 2009 PST (permalink)

view photostream

MarkRebuck says:

(self-followup)

I didn't see the thread from several months ago. Silly me :-). Looks like the question has been answered here before.
72 months ago (permalink)

view photostream

alan_sailer is a group administrator alan_sailer says:

Hey Mark,

You are on the right track with the article you linked. He even built his own capacitors, hard core.

There is an old article from Scientific American about color schlerien photography that describes the old Edgerton microsecond flash. that's how I started building my flash.

If you are serious about this project, get in touch and I'll give you some tips. Dangerous electronics, so be serious.

Alan Sailer
72 months ago (permalink)

view photostream

Mohammad J Al-Mumen says:

Hi,

Do you know If anyone build and sell those air-gap flash units?

thanks.
52 months ago (permalink)

view photostream

Maurice Ribble says:

The only company that I know of that ever made and sold these was EG&G. Here is a link to the manual for their product: people.rit.edu/andpph/text-microflash-549-manual.pdf

Sometimes you can find these on ebay, but they are expensive and I've never seen one in real life.

I have also made an air-gap flash with some help from Alan. My design is simpler than his, but he his has a variable voltage option which is nice. I'm planning to write an article about the flash I made in the next month or two after I've done more testing with it and refined a few pieces.
52 months ago (permalink)

view photostream

P^2 - Paul says:

How much are you wanting to spend?

A successor to the 549, the SPOT: prismscience.com/spot_specs.php

And its big brother, the MegaSun: prismscience.com/megasun.php
52 months ago (permalink)

view photostream

Maurice Ribble says:

Here's a blog post about the air-gap flash I made. www.glacialwanderer.com/hobbyrobotics/?p=490
50 months ago (permalink)

view photostream

johnnicol_21 says:

depend on how much you want to spend have a look at www.highspeedflash.com
50 months ago (permalink)

view photostream

Stuart Hirth says:

I think you've covered it, but there are two mobs that do ultra highspeed flashes that I can find. One lot in the UK mentioned above by johnnicol21 "microFLASH pro is our standard system designed for the professional photographer. microFLASH ultra is an ultra fast system designed for ballistics work." but they aren't cheap. Same also with Prism Science Works (search on SPOT). The main difference for me here in Australia is the flash units from UK can be exported worldwide and the Prism Science Works cannot as they don't have their export license for that product. So I am in that same boat as you all, I am at the limit of all my home-grown xenons and have to go air-spark!
48 months ago (permalink)

view photostream

FKhan55 says:

There are some very old posting here. I just signed up for flicker and would like to help anyone make an airgap flash. I have designed a DSLR compatible digital trigger that is not a part of other AirGap flashes out there. Also, I have added some features such as Charge and ready LEDs so you know that the High voltage is present in the unit.

There is a discharge IGBT based system that will discharge the 25KV capacitor. I am also thinking of adding a small panel volt meter so the user knows the actual voltage present at all times.

I hope this helps.

I will post my designed once all is in place.

Most parts are readily available from electronic supplier.
39 months ago (permalink)

view photostream

Murat-C says:

I migh be interested in the DSLR compatible trigger, any specs?
39 months ago (permalink)

view photostream

stevegreen1953 says:

Add me to the list of people that would be most interested in a well behaved trigger unit. I have plenty of caps and transformers from my Tesla coil building days.
Originally posted 39 months ago. (permalink)
stevegreen1953 edited this topic 39 months ago.

view photostream

Gomez Addams says:

This is fascinating. I may chip in from time to time, as I fiddle with high speed pulsed power stuff, but I have too many projects on my list to think about building a really fast light source. Unless and until I need it for, say, taking pictures of railgun armatures in flight, which just isn't a high priority for me.

But yesterday I stumbled across a pointer somewhere (maybe even in this group? I can't remember today, sorry) to an argon jet guided spark gap light source. The jet of argon comes through a hole in one of the gap electrodes. This same hole is also the orifice through which the arc is imaged with a condensing lens.

I'm aware argon is not normally a preferred medium because of its long quench times under normal (arc lamp) conditions. This jet business is clearly not normal arc lamp conditions. Authors claim flash durations approaching 1x10^-7 seconds. It has been used for Schlieren photography.

I'll paste a link here, if it doesn't persist, try a Google Scholar search on "short duration" appearing with 'spark' and with "light source". That's all my link is. Most of the white papers will require access to IOP, IEEE, etc. Most libraries can get you access for free, but you may have to show up, depending on how good yours is.

Another option to consider is exploding wires. In all of these emissive plasmas, brightness goes with the square of the current (among other things, if you really get into the equations covering simultaneous radiative losses, it's certainly over my head) during the pulse, generally speaking, and so the faster you can stop the current - clearly - the faster you can hope for the brightness to quench... _all_other_things_being_equal_ (for spherical elephants on frictionless planes, etc, etc). SO: since Z-pinch is a really terrific way to cut off current in a big hurry - and true exploding wires do this really well - it's something to be explored.

You want to avoid wire metals that are likely to combust in air (generally speaking the lighter metals) - and anything whose vapor is toxic (most of the heavy metals) or consider putting the whole affair inside an artificial atmosphere - indeed, consider a high mass, difficult to ionize gas (SF6 anyone? too bad the price shot up) to act as a coolant/quenching aid as well as to prevent combustion, then you can use whatever wire works best otherwise. I'd personally guess silver, but copper will do in a pinch. {sorry} You need really fast caps and a low inductance current path, obviously.

-=Wear hearing protection=-. Seriously. Keep your mouth closed. Consider swimmer's nose-clamps to pinch your nose shut. I've done exploding wires (just not as a light source) - and this is the voice of experience speaking. Unless you're some exceptional masochist who would actually enjoy the sinus headache from Hell.

An exploding magnesium wire in a pure oxygen atmosphere would be bright indeed, but the flash would probably be milliseconds long! A quick search shows others have thought of this exploding wire light source thing - I haven't read any of the papers yet.

I apologies if these ideas have been covered here already. I'm a bit absent-minded. Oh, I have a thing to say about used pulse caps, I'll post that separately.
35 months ago (permalink)

view photostream

Gomez Addams says:

A word about used pulse caps. Pulse duty caps are specified for a shot life. Shot life can be fairly accurately predicted if you know all of the parameters of the system (as you'd damned well better if you're designing circuits which utilize caps costing anywhere from $1,000 to $100K each). An intro is here:
home.earthlink.net/~jimlux/hv/caplife.htm

As a consequence, big pulse caps are pulled from service and surplused when they approach 90% of their predicted shot life.

Paper logs are supposed to follow the bigger ones around, because many projects don't approach the shot life of the caps they paid for, and (for example) the guys building Saturn really needed to know what the caps from PBFA-I had _really_ been through. Programs tend trade these assets around quite a lot.

Oh, and failure modes on some of these caps can be quite messy. They aren't likely to explode and kill of your neighbors, or even injure you, most likely. But they can spooge oil all over the place, and no one wants that.

But this apples also to the little Maxwell capacitors that come out of lasers, defibrillators, lithotripters, etc.

By the time YOU get your hands on one, from eBay, or The Black Hole, or even (gods forbid) Surplus Sales of Nebraska, no professional pulsed power jock would touch them with a ten foot hot stick.

BUT: I'm not saying they're worthless. You'll likely pay a small fraction of the original cost, and provided you operate them _very_ conservatively ( consider half the rated charge voltage, and watch that voltage reversal!) they may be an okay deal for you, depending on your budget.
Originally posted 35 months ago. (permalink)
Gomez Addams edited this topic 35 months ago.

view photostream

alan_sailer is a group administrator alan_sailer says:

Gomez,

Can't say much about the guided argon flash or exploding wires since I am not familiar with the tech.

It is hard to argue, though, with the simplicity of the air gap flash.

Most people I have had contact with are intimidated (for good reason) with the high voltage aspect of the air gap flash. Argon/wire technology would still involve high voltage so.....

As per your second post about life it is a point well taken. They are used in fact.

My personal experience with the Maxwell 35kV/0.03uF cap (which I find all over the net) is that I have had no problems with any of them. They cost about 100$ vs 700$ new. The pulse rate used as a air gap flash cap is about .01 Hz so even if there are only a million discharge cycles left, you have a long way to go before failure.

And finally, the total energy is that cap, even charged up to 35kV is about 20 joules, which just isn't much. The case is pretty tough plastic, looks like polypro, I'd be surprised to see any leaks on failure. According to Maxwell (now General Atomics) the fill oil is not anything toxic like the old style PCBs.

Just my opinions, your mileage may vary.

Cheers.
35 months ago (permalink)

view photostream

Tony Hamilton says:

Guys, iv got a project to work on, all sales of images are going to be for charity, but im not able to buile an Air Gap flash! im afraid its WAY above my ability..
What im asking is, are there any products i can BUY at a reasonable price? or can these things be hired anywhere? Im in London UK and have lots of photography shops ect but none seem to know where to source a fast flash!..

Thank you for reading..

Tony..
27 months ago (permalink)

view photostream

alan_sailer is a group administrator alan_sailer says:

Tony,

I have no idea what you consider a reasonable price.

But I would guess that the Spot unit from Prism at about 4000$ would not be reasonable to you. It would also have to be imported as it is build in the USA.

If you do get an air-gap style flash, be warned ahead that they are very big compared to a normal off-camera flash and they are really dim compared to same. Say maybe a GN of 10-15.

Cheers.
27 months ago (permalink)

view photostream

Tony Hamilton says:

Thanks for the info Alan, im surprised the air Gap is so dim, but iv been using my SB900 at 1/64th so should imagine its about the same brightness.. its just sourcing one (or two!)

4K for a flash! it would have to be as bright as the sun for that price! lol..

Thanks again..

Tony.
27 months ago (permalink)

view photostream

alan_sailer is a group administrator alan_sailer says:

Tony,

Xenon adds a lot to the brightness. Unfortunately, it has a pretty long excited sate, which is a fancy way of saying that it keeps putting out light even after the electrical stimulation has gone away. Think of it as afterglow, but bright.

I am only guessing, but the relative lack of microsecond pictures may be due to the fact that it's a potentially expensive hobby.

Prism also makes the MegaSun, a super bright lighting system. Not as fast, but they describe lighting areas the size of a football field.

Cheers.
27 months ago (permalink)

view photostream

Tony Hamilton says:

Thanks again Alan, i dont need LOTS of light, just FAST light.. as i said, its for a charity project im getting underway IF i can find fast light.. im quite happy with my SB900s for my own little projects, but for what i have in mind they just wont do what i have in mind! You have shot very similar to what were trying to achive but there will be a fairly exciting twist to ours, we have some VERY high (Or in fact LOW) profile assistance.. i just need to get the lighting i need, i could perhaps make do with not completely freezing the action, but its a compromise im not keen on..

a couple of air gaps would probably be good enough at a guess..

Tony..
26 months ago (permalink)

Would you like to comment?

Sign up for a free account, or sign in (if you're already a member).