How much light does 1/6000 need?

Discussion in 'Beyond the Basics' started by support1, Apr 3, 2008.

  1. support1

    support1 TPF Noob!

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    Hi everyone,
    I'm planning to start shooting fast moving or falling objects at 1/6000s. Flash strobes can be synced to 1/200 so I need to turn towards continuous light and here's my question: how much light (in Watts) I need to shoot at this shutter speed? Does anyone have any experience with this kind of shooting?
    Cheers
    Paul
     
  2. JimmyO

    JimmyO TPF Noob!

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    1/6000s is blooddy fast. Even when im using 1/4000s i have to be outside on a very bright day at noon. How fast is what your shotting? I wouldnt think u would need to shoot that fast.
     
  3. Helen B

    Helen B TPF Noob!

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    The shutter speed might be 1/200, but the flash duration will probably be quite a lot shorter than that (1/1000 or thereabouts maximum), especially when used at low output.

    Therefore the best thing to do is to make sure that the ambient light is insufficient to create a blurred image, and just rely on the flash exposure.

    Most portable flashguns control their output by shortening the flash duration, so the closer the flash is to the object the shorter the duration of the flash - down to around 1/10,000 to 1/30,000 second, depending on which flash you get. Most manufacturers give that in the spec.

    Non-automatic, studio flashes may not use time as the output control - in fact they may have a longer flash duration at lower output.

    In general, continuous light is totally inappropriate for high speed still photography. Just suppose that you have a flashgun with a 200 Ws output (eg the Metz 60 series). At 1/64 power it has a flash duration of 1/5500 sec and an output of about 3 Ws. As that lasts 1/5500 s, it is like a 17 kW light during that brief period. Even if you used a continuous light source that was twice as efficient as the flash tube, that would be around 9 kW. 9 kW of high efficiency continuous light is very expensive. Way more than a second-hand Metz 60CT series for $150 to $200. If you used incandescent lamps, you would need about 30 kW. These are just ball-park estimates to give you an idea of the magnitude.

    The Metz 60, though powerful, might not be the best for high speed use, by the way. I just used it because I have the numbers at hand. It has a 1/200 s flash at full output, so you need to reduce the output quite a lot to get a short burst like 1/6000 s. It would probably be better to start with a flash that has a short burst at full output, so you only need about 1/8 output to get to 1/6000.

    Best,
    Helen
     
  4. support1

    support1 TPF Noob!

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    Well the whole idea is to freeze drops of water and they need to be real sharp. Talking about flashguns, I have a Nikon SB-800 which is absolutely great peace of equipment but I'd need to be using it as a remote (SU-4 and 2-3 light sources) so in this mode I think high speed flash sync is unavailable. And in this case I'd have to use it at high output I'm affraid. High output synced with 1/6000s...tough job.
     
  5. renegademaster88

    renegademaster88 TPF Noob!

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    I did some water studies on a fountain nearbye in daylight. I tended to shoot at about 1/2000. A just your ISO to get the shutter speed you need. I was at about ISO 400, which is fast but not too grainy.

    As to power, as much as you can get i guess, and try to get towards ISO 100 or even 50 on some cameras.
     
  6. Helen B

    Helen B TPF Noob!

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    Can you control the ambient light? If so, then you don't need high speed flash sync to get 1/6000 s exposure. You can sync at 1/200. How far from the light source to the subject? What aperture do you want to use? What ISO? If you can answer these, we can tell you how much light you need, either flash or continuous.

    Best,
    Helen
     
  7. selmerdave

    selmerdave TPF Noob!

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    What Helen said, with flash photography your shutter speed is not freezing the subject, it's the flash. You could freeze a bullet with a 1/2 sec. shutter speed, because it's the duration of the flash output that is freezing the subject. The vast majority of the time that the shutter is open it is not capturing any image because the ambient light does not allow sufficient exposure (and that's the way you want it - less ambient light to make sure of that). Choose your shutter speed based on whatever will sync with the flash, and then focus on using the flash to freeze the subject.

    Dave
     
  8. support1

    support1 TPF Noob!

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    I guess I'll try shooting with one flashgun first and see the results. Thank you all for your comments and suggestions
     
  9. Socrates

    Socrates TPF Noob!

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    You can use a strobe in FP mode with 1/6000 second but the total light volume is still a concern. You'll need an ISO of several thousand to compensate for the shutter speed.
     
  10. Helen B

    Helen B TPF Noob!

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    I've just looked in the manual for my SB-800 and it lists the flash duration at 1/8 output as being 1/5900 s, with a guide number of 14 m at ISO 100 and 35 mm equivalent coverage. That's a light output of about four times what the Metz 60 CT-4 is capable of at 1/6000 s.

    The equivalent kW rating for continuous light would, therefore, be about four times the already large numbers I gave for the Metz.

    Best,
    Helen
     

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