Concept 2 Innovation

High-Speed photography

At the request of his older brother Alan, Greg started looking into building portable very high speed flash equipment around 1983. During the first year of looking into this problem Greg decided that high-power portable (and safe) Xenon flashguns could not be made. However, this turned out to be a niggling problem that simply wouldn’t stop eating away at him, so over a period of a couple of years he put together a few prototype systems until he came up with something that met specification.

In order to meet his own stringent safety requirements (he knew his brother would be working near water, and occasionally be caught out in a downpour of rain) Greg built the whole unit in a watertight polycarbonate case with a clear lid for the light to escape. The only external component was the 12 volt battery to power the unit. This meant that everything at high voltage sat within the waterproof box and there were no external leads of any kind carrying high voltage.

The units contained a high power inverter turning the 12 volts from the battery to 3,000 volts D.C. at a current of 50mA, the Xenon flash tube and trigger circuitry, and the energy storage capacitor. The energy storage capacitor is of the “paper” type, i.e. non-electrolytic, and early units had 100 Joule capacity, whereas later units utilised 200 Joule capacitors. Discharge times were around 1/40,000 second or 25 microseconds – so these are formidable pieces of kit generating 8 Megawatt pulses of light!!

Below you can see what 200 Joules of light energy being let loose in 1/30,000 second will give you in terms of a photographic result:

Archer Fish sizing up his target – image by Alan Parker:

A popping balloon frozen in time – image by Prof. Greg Parker:

An exploding light bulb at 1/30,000 second – image by Prof. Greg Parker:

A swallow entering a barn at full lick – image by Alan Parker:

It is probably worth running through a few straight facts about high-speed flashgun systems (without divulging any IP) so that you may consider routes to carrying out high-speed photography yourself.

Having worked in this area for over 25 years, I personally haven’t come across any one subject in photography that has generated more smoke than HSF, and I really don’t understand why this should be the case as the basic concepts are very easy to grasp. We need a pulsed source of light, with quite a few Joules of energy in the pulse, and the pulse duration needs to be short. That’s all there is to it really, and we only see the pointy little horns as we get into the fine detail.

First the energy. The energy you require to properly expose your film, or illuminate your CCD, depends on the f# you are working at, the distance to the object you are illuminating with your flash, and the ISO setting of your CCD or the ISO rating of your film. As a reference you can assume a 200 Joule pulse of light will give you correct exposure using ISO 100, f#32 at 6 feet (2 metres) – you can scale the energy required for different f-numbers, distances and ISO settings in the usual way.

Second the flash duration. At 1/10,000 second you will stop the larger birds in flight if their wings are in the right position (at the end of an upstroke or downstroke). You will not freeze smaller birds in flight and you will not freeze most insects in flight. At 1/25,000 – 1/30,000 second you will capture hummingbids in flight and you will see feather detail on larger birds in flight. You will not capture feather detail of larger birds in flight using 1/10,000 second light pulses as the blur length is of the same order as the feather detail.

An ordinary electronic flashgun such as they type that sits on top of your camera is often thyristor controlled to save energy, and sometimes you can actually “dial in” the speed of the light pulse by effectively cutting down the energy in the pulse. So, although the “full power” mode of an ordinary electronic flash may give you 200-300 Joules (for a big powerful unit) it will normally do this in a pulse length exceeding 1/10,000 second and may even approach 1/1,000 second. No problem you say – I can cut down the power and get a shorter pulse length. Correct – you can, but to get down to 1/25,000 second or thereabouts, you will be working at 1/32 or 1/64th power – so yes you will get a 1/25,000 second pulse of light, but it will only contain a few Joules of energy, maybe 4 or 5 Joules if you’re lucky. O.K. so then I’ll build a rack of these flashguns, maybe have 6 of them coupled together and that will give me a respectable 30 Joules or so of light energy at 1/25,000 second. Well yes you can, but now go back to the energy requirement figures and you’ll see this means you have got to stick your array of flashguns within a couple of feet of a hummingbird, which apart from being unfair on the bird, also means quite a bit of Photoshop work cloning out half a dozen highlights from the poor bird’s eye. I hope you are getting my point, there is no “easy” solution to the high speed flash problem. There is a solution of course, you build a unit capable of kicking out 200 Joules in less than 1/25,000 second – but this is quite difficult to do, and impossible to do using the components normally found in your standard thyristor cut off flashgun.

The common or garden thyristor cut off flash gun uses an electrolytic capacitor to store the light pulse energy, and the unit typically works at around 300 volts. Electrolytic capacitors are used as they are great for storing lots of energy in pretty small volumes. They are not great in that they cannot discharge very quickly due to a thing called internal resistance, and this you cannot get around. Yes you can do fancy parallel tabs to minimise the resistance as much as possible – but it’s always sizeable, and it will always slow you down! You can series up the electrolytics if you like and work at a higher voltage, but unfortunately this won’t speed anything up as you still have the same series resistance per capacitor. So what do you do? You have no option but to go to “paper” or mylar film-type capacitors which have tiny series resistance, and tiny inductance (so they discharge VERY quickly). But unfortunately these come in much smaller capacitance values than electrolytics, and Farad for Farad they are MUCH bigger than electrolytics. So its trade-off time. You pick a size and capacitance value that you can work with and then choose the working voltage to give you the energy you want. A custom made mylar film capacitor measuring maybe 4″ x 4″ x 3″ can give you 45uF of capacitance and for 200 Joule light pulses you’ll want to charge this to 3,000 volts – ouch! Here’s another reason the camera boys don’t sell these to fit to the top of your DSLR. However, connect one of these beauties across a linear Xenon flash tube (of the type used to fire lasers) and you will get an intense pulse of light suitable for taking very high speed pictures with a suitable distance between your flash unit and the subject.

This is what Parker Technology has done and developed over 25 years. There is no work around for this problem that I am aware of. If you believe there is a work around – please let me know about it

February 2009:

I have taken delivery of a set of specialist high-speed high-power flashguns from http://www.highspeedflash.com/ The units include 2 x “Pro” series flashguns and one “Ultra” unit. The image below shows several glass “pebbles” dropped into water and photographed using a single “Pro” unit.

I used a home-built sound trigger to synch the action, Camera Canon 40D, lens 100mm macro, f#22, 4 feet, ISO 100.

The image below shows an airgun pellet penetrating a potato taken using an “Ultra” unit and home-built sound trigger. ISO 100, f#22, 3-feet, Canon 40D and 100mm macro lens. This was only a test shot to check the speed of the “Ultra” – I shall choose more photogenic subjects in future

March 2009:

I have spent this afternoon taking test shots with the Ultra unit – subject – good old popping balloons. Canon 40D, ISO200, f#25, 2 feet, sound trigger. Here’s a single result from around 10 nice freeze frames.

April 2009:

I have just returned the two “Pro” units to highpspeedflash dot com to exchange them for two “Ultra” units. It became clear to me in using the units that I am more interested in very high speed studio work rather than outdoor Nature photography – so the “Ultra” units are more appropriate than the “Pro” units for my applications. Eagerly awaiting the arrival of the “Ultra” units so that I can begin to build up a large portfolio of very high speed flash images.

May 2009

Parker Technology are now the proud owners of a set of three “Ultra” units which are availablr for you to hire for your promotional/metrology/specialist photographic requirements. Prof. Greg Parker will bring these units along to your shooting location for you to use for your assignment. Each “Ultra” flash provides a 1/111,111 th second light pulse at 50 Joules – so this lighting system represents a totally unique photographic facility. Book your “Ultra” imaging session by contacting Greg at Concept2Innovation right now!

July 3rd 2009

Today I used all three “Ultra” units to do some real ultra high-speed flash photography. This image of a light bulb shot using an ait rifle pellet has an exposure time of just 9 microseconds and was taken 5 milliseconds after the pellet was fired.

July 4th 2009

And today I managed to get some more HSF work done This time it was the eggs’ turn to interact with the air rifle. The reason why the single egg landscape image is so wide can be seen off to the far left – there’s the pellet continuing to go on its way.