Why use a flash unit from HIGHSPEEDFLASH.COM?
If you want to do true outdoor nature photography (Birds, Insects, etc.) you cannot get away with underpowered solutions like coupling together commercial units and stopping their power right down to get high speed. The plain fact is you need a purpose-built high-power unit.
It has been stated that you don't need HSF units as fast as these to photograph birds in flight but this is fundamentally incorrect! You may be lucky with larger birds, with their wings in the right position (end of stroke) to get a reasonable looking shot - but what about smaller birds, and the fine detail? By the fine detail we mean being able to resolve feather detail in a fast moving small bird. You might just about freeze the wings if you are lucky - but you will not resolve fine feather detail as this will get washed out completely by the bird's motion.
A single unit gives out 150Joules of light per pulse with a pulse duration of 1/28,000 second. Wildlife photographers normally use three of these units synchronised together.
Why are high-speed flash units so expensive compared to electrolytic systems?
Prof. Greg Parker - Saturday, 06 November 2010
A number of people have asked the above question, and they also wonder why an electrolytic capacitor system can’t do the same job as a specialist HSF unit. I will try to answer these important questions.
Our high-speed flash guns use high voltage polymer capacitors which have very low internal resistance and also very low inductance. The low intrinsic resistance and inductance of these specialist (i.e. expensive) capacitors means that they can discharge their full energy extremely quickly, the only downside is that it is not possible to get big values of capacitance (measured in Farads) in the small volumes that can be achieved with electrolytic capacitors. This means that in order to get high energies stored in our HSF units we need to work at high voltages (which in turn means more expensive components) as energy is related to voltage and capacitance by E = 0.5 C V2 where E is the energy in Joules, C is the capacitance value in Farads and V is the charging voltage in Volts. Electrolytic capacitors can have rather large capacitance values in quite small packages, but they are typically voltage limited to a maximum of around 500V due to the physics of their construction. As the stored energy goes as the voltage squared and only linearly with the capacitance, this shows another advantage of the high voltage polymer capacitor for HSF applications.
However, many of you will be aware that the big electrolytic units can be made with “thyristor cut-off” - a really neat trick which not only saves energy, but also produces a faster light pulse. So why can’t you just build a big electrolytic unit with a thyristor cut-off circuit to mimic the specialist high-speed flashgun? This is where the internal resistance and high inductance of electrolytic capacitors comes into play. You simply cannot get the energy out of electrolytic capacitors quickly enough due to their intrinsic internal resistance/inductance, and that really is the whole problem with trying to get short, high-energy light pulses out of electrolytic capacitors. The polymer capacitors have incredibly small internal resistance/inductance values and so they are able to discharge their full energy extremely quickly indeed.
But surely I can make an electrolytic system as big as I like, so I can pulse shorten to get the energy value I want in as short a pulse as I want, can’t I? Unfortunately you can’t, the properties of the electrolytic capacitor don’t allow you to scale up like that, the internal resistance scales with the capacitance value so that you quickly enter the “diminishing returns” region. This is why the biggest commercially available (non-studio) electrolytic units run at something like 300 – 400 Joules with an intrinsic (i.e. full) discharge time of 1 millisecond (1/1,000th second) or even longer! When you start pulse shortening using the thyristor cut off you quickly lose out on pulse energy to get the short discharge times, so you will typically be at 1/32nd full energy if you want a pulse length of 1/28,000th second or less, in other words you will be down at the 10 Joule level. A Pro unit by comparison gives out 150 Joules in 1/28,000th second, a useful amount of energy allowing the photographer to use larger f-numbers and bigger working distances than the high-power electrolytic system.
Another possibility of course is to buy and link together a number of high power electrolytic flashguns to try and mimic the specialist high speed flash, and some people do of course do this. The problem with this approach is that the multi-gun system is now even more bulky and even more expensive than the specialist HSF system, plus it is likely to have inferior performance as well (multiple sources of light which show up in reflections, problems with synchronising all the guns precisely without trigger jitter being apparent) and a host of other problems.
So the answer to the initial question is: specialist high-speed flash systems are not more expensive than electrolytic systems capable of doing a similar job. In fact they are considerably cheaper, smaller and have fewer operational issues.
Prof. Greg Parker
Saturday, 06 November 2010
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