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If I'm photographing a bathroom shower, using flash, the fall-off of the light from the flash is such that the water droplets appear to fall upwards. That is, they appear large at the top and narrower towards the bottom of their trail. I understand that this is an optical illusion and is due to the way that the flash head emits a burst of light at full power almost instantaneously but then the light "falls away" over the following 1/1000 sec or so.

How can I avoid this? The possible effects I've seen which might work for me would be:

  • a continuous stream of water
  • have a flash profile such that trails of the water droplets appear to narrow towards the top
  • discrete drops rather than trails

The equipment I'm using is:

  • Nikon D7100
  • 50 mm f/1.4 lens, though others are available
  • Elinchrom D-Lite 4
  • Use first shutter curtain flash? Have you got examples of what you don't want? – BBking Jul 12 '14 at 7:36
  • Have you tried using lower flash power? There should be less (but still some) fall off than what you experience at full power. – Michael C Jul 12 '14 at 9:04
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    @MichaelClark - The DLites are full-cycle flashes (that is, the output power depends on the capacitor charge); the flash duration gets longer as the power goes down. – user28116 Jul 12 '14 at 9:35
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    It's not only an optical illusion. Water droplets do not look like the "cartoon" drops we see everywhere. Have a look at static.photo.net/attachments/bboard/00L/00L9fF-36529984.jpg and static.photo.net/attachments/bboard/00L/00L9fH-36530184.jpg from photo.net/nikon-camera-forum/00L9fF – Håkon K. Olafsen Jul 12 '14 at 11:07
  • @HåkonK.Olafsen It's nice to see proper evidence of what I'd heard - they make a very useful addition to this Q&A! It's why I made a point of saying "appear to" throughout my question. – ClickRick Jul 12 '14 at 12:47
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Unfortunately, your flashes won't be able to do the job. It's not that the DLites are altogether useless (they're really rather nice units), but the way they work — the way a lot of studio flashes work, and not just at the lower end — means that the flash duration at t 0.1 (the time when at the flash is firing at more than 10% intensity) is as short as it's ever going to get somewhere between half and full power. The lower you bring the power down, the worse it gets. Your spec sheet will show the t 0.5 going up quite a bit as you reduce power, but the t 0.1 goes up even more. It's just not a good motion freezer. (Nor are the AlienBees, Elinchrom BRX, Style and pack-and-head systems, Speedotrons, Bowens, Photoflex, Profotos other than the new B1 Air monolights,... the list goes on and on.)

Elinchrom makes one monolight, the ELC Pro HD (in two power levels) that will work. The Paul C. Buff Einsteins will do the trick at less than half the price. Most Hensels will work. The Profoto B1 Air (the new battery monolight) will work. So will the whole of the Broncolor line (like you wanted to hear that at the prices they charge).

What all of these flashes have in common is that they control flash duration by cutting off the power rather than changing the charge on the capacitor(s) — just like speedlights do (usually using IGBT devices). And that may be your real answer if you aren't going to be trying to freeze fast motion often: it can be a lot cheaper and easier to beg, borrow and/or steal a bunch of speedlights for a single shoot than to invest in a new flash system (especially when there aren't many IGBT studio units at the lower end of the price scale).

You'd probably need to double, triple, or quad up the speedlights to keep the power down and the flash duration short. And if you can narfle enough Nikon (or at least iTTL-compatible) units, you even get the option of using rear curtain sync so any remaining ambient will give you fat-at-the-bottom drops.

  • +1 for a lot of this content. It would have been +2 but for the Broncolor suggestion :P I shall try the iTTL direction, though, and report back. – ClickRick Jul 12 '14 at 12:57
  • I've been able to borrow an SB-800 today and you're right, it freezes the drops beautifully! flickr.com/groups/strobist/discuss/72157632234798676/… has some numbers for the SB-800 at different power levels so I shall play with that. Rear-sync is a possibility but I'll have to play with balancing ambient light levels. And I'm now going to have to build my own modifiers for it as I had already done for the Elinchroms. Other than that, job done! – ClickRick Jul 12 '14 at 16:38

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