Flash Duration

Flash duration measurements

Canon, Buff (Einstein), and Microflash Pro units were evaluated. I made these measurements were made with a sensor manufactured by Electro Optics Technology, a ET-3000 InGaAS (900-1600nm). While this sensor is not designed to operate in the visible wavelengths, flashes emit energy in the infrared that was used for the measurement. Recently, flash duration measurement capability has been incorporated into exposure meters such as the Sekonic L858D-U. The numbers in the table below are consistent with others reported online, and also, in a relative sense they are consistent with my table saw measurements (see below).

At one point I was optimistic about the Microflashpro unit. I had an opportunity to evaluate it. I hoped it would be the best solution, at one hundred times the energy of the Canon flashes and with an advertised flash duration of 36 microseconds. But alas, measurements show that the duration is really no better than an Einstein flash which cost 5 times less. The Microflashpro lamp is a cylindrical configuration about 300 mm long. One plus is that at 150 joules, you can equip it with a DIY softbox and still have plenty of light. It is f/32 at 2 meters, ISO100! It will overpower the sun, so in theory you could walk around your garden in any lighting situation with a 150 joule, 130 mircosecond flash! Essentially all the light for the image would come from the flash. But in practice the Microflashpro is heavy and hard to work with. Energy is not adjustable. It weighs over 10 kilograms and it is about the size of three bread loaves placed side to side to side. Although it has 3/8-16 and ¼-20 tapped mounting holes, it does not take to a tripod well. The company makes another version, much lower energy, similar form factor, with an advertised duration in the microsecond range, if you can believe that.

Measured Flash Durations for some Commercial Flashes

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Figure: Flash Curves for Canon 550EX and 430EX flashes at 1/8th, 1/16th, 1/32nd, and 1/64th energy. Plotted is relative power vs. time in microseconds.

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But you do not have to use a fast detector, or even rely on what the manufacturers might tell you. You can measure it in a relative sense. I compare flash duration between models, brands, and identical units of the same model as follows. Mark some radial lines on a table saw that rotates at high rpm, such as 3600 rpm. Take some photos of the spinning blade at different flash energies. Your flashes are not likely to freeze this motion, but just compare your blurry results in a relative sense, energy to energy, flash to flash, brand to brand.