I need a high energy flash, very bright with a relatively long pulse duration otherwise my short exposure time photos have half of the image dark, because the light pulse has ended before the mechanical shutter has rolled all the way across the sensor. After trying out a few products it seems the flashes I need are over £1000.

I know next to nothing about photography, but I know a fair bit about electrical engineering, and I think I could quite easily build the flash I need for much much much less. To get brightness and a longer pulse I just need lots of big flash capacitors, a xenon bulb that can handle the duration and frequency of flash, a simple trigger circuit, and careful thought about impedances.

This worries me though, what about these professional flashes makes them so expensive? Will my home made flash produce bad images because of something I have overlooked?

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  • Well, there are some cheap flashes that support high speed sync (1/8000), like YN-568EX. Cost is another issue here.
    – Rafael
    Sep 1 '15 at 1:13
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    The classic solution has been to shoot in a relatively dark environment, use a relatively slow Tv, and let the short duration flash freeze the motion. What is it about what you are shooting that can't be done this way?
    – Michael C
    Sep 1 '15 at 1:13
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    Why are professional X so expensive? The answer is pretty much because a more demanding product for fewer demanding users with more income :)
    – Itai
    Sep 1 '15 at 4:46

I don't know your special situation, you did say high energy, but I don't know scale. You want a fast shutter so I assume you want a high speed photo. Perhaps you may need significantly greater power, but in contrast to your stated goal, I can tell you about photography. One problem with a fast shutter speed is that it decimates the longer light, which can only work when the shutter is open. Watt seconds of energy (joules) is watts x seconds (and 1/2000 second is a very small multiplier).

In reasonable situations, the normal solution is to use a slower shutter speed, not exceeding the cameras maximum shutter sync speed (typically around 1/200 second). Then the shutter is fully open and the camera can sync the flash. The shutter merely needs to be open to pass the full watt seconds of the flash pulse. Then shoot in dim ambient light, so that ambient at 1/200 second will not blur anything.

If the ambient is dim, it does not matter how long the shutter duration is open, since there is not enough light to matter. Not meaning black, reasonable room light can work if the flash is significantly brighter (maybe 3 stops brighter) and the shutter is not toooo long. Such an exposure without the flash should come out black (which is very easy to accomplish). But you can also dim the lights if a problem. Not necessary to be so dim that you are unable to work. If the ambient light is too dim to register, the shutter speed cannot blur anything.

See http://www.scantips.com/speed.html. These are taken with Bulb shutter, manually operated to be around 1.5 seconds shutter time. If the flash pulse is very long, it will blur the motion. And big flashes do have long durations. Note flash durations (except IGBT speedlights at less than full power level) are spec'd as t.5 times, 50% power points.. actual duration is more than 3x longer. But if the flash is much faster (speedlights), it will stop motion, and the shutter merely needs to be fully open. A regular camera speedlight (maybe $100 class from China) at low power level (to be extremely fast) normally has adequate power if mounted close (maybe guide number 20 at ISO 100 and 1/32 power, meaning f/20 at 1 foot, or f/1 at 20 feet). With maybe 1/17000 second flash duration, which will stop almost anything. At any slow shutter speed if ambient is not bright.

Larger studio lights for portraits will not normally be very fast. Large flashes are slow (large capacitors are slow). One possible exception if you need more than a speedlight is the Einstein flash, from http://www.paulcbuff.com/e640.php Pretty large, but it has a fast speedlight mode. Few others do.

If the flash is big enough and slow enough, and you do use a fast shutter speed like 1/2000 (that cannot sync), but the flash will be slow enough to last for the full shutter travel time duration (of the open slit as it moves down the frame), maybe 1/200 or 1/300 second travel time... but the flash pulse will be fading out dimmer all during this trailing tail, exposure will not be even as the shutter slit moves down the frame. Pocket Wizard radio triggers have a special mode called HyperSync that delays the shutter to only occur in the trailing tail, i.e., without the large initial peak, striving for a bit more consistency, but at much lower power level... All these things have been thought of. None are perfect.

If building, you might research Dr Harold Eugene Edgarton, who invented high speed flash in the 1930s at MIT. A few of his patents are on line, and he did big things during and after WWII. Typically his special speed goals used high voltage (~2000 volt) with small capacitors (1 or 2 ufd to be fast). Energy is 1/2 CV² . Big capacitors have slow RC times. Low voltage is slow.

But again, fast shutter speed is counterproductive, the fast flash does the timing.

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