Long flash duration = high speed sync?

Discussion in 'Lighting Equipment' started by jefffitz, Feb 6, 2012.

  1. Hello! So I know that the shorter the flash duration of a flash unit is, the less motion blur will be introduced into an image of a fast moving subject. But if the flash duration was really long, longer than the sync speed of the camera (1/250), would it be possible to sync at higher shutter speeds? My understanding of how faster shutter speeds are obtained is that the curtains move at the same speed, 1/250, but they create a progressively narrower moving slit to expose the sensor to less light as you increase the shutter speed. So if a 1/8000 shutter speed was still moving the curtains for 1/250 of a second, that would mean that if the flash duration was also that slow, it would be lighting up the scene for the entire duration of the exposure. Is this a fair assumption to make? I'm sure the intensity of the flash would change over the course of the exposure, but it seems to me that you could potentially get a reasonably acceptable image this way. Any thoughts?
  2. The flash's "tail" does fall off precipitously, even if it lingers for a while. This is exactly why manufacturers' hot shoe flashes actually pulse multiple times, very quickly, when the flash and the camera agree on the fact that high speed sync is happening. But each of those pulses has to be dialed way back in order to reserve the power needed to make all of the pulses the same power (for even light across the frame, as the shutter travels).
  3. This was essentially how an FP-class flash bulb worked. They had an extremely long burn duration compared to the regular bulbes normally used with leaf shutters, allowing the shutter slit to completely traverse the frame.
  4. As stated above, you are essentially correct in that if the flash duration lasts for say 1/200 of a second then it will expose the whole image without any dark banding. However this length of flash duration only occurs when the flash is in FP mode (aka high speed sync).
    If the flash is in normal modes then the flash duration is anywhere around 1/2000 - 1/4000 of a second, so if the shutter speed is set to anything above the flash sync speed (most commonly 1/250) then you will get a dark band along one side of the image.
  5. I was looking at Paul Buff's White Lightning strobes and I believe their highest powered model at full power has a flash duration of about 1/300th. I wonder how well that would work. Hmmm.
  6. You would need to see the light output graph to tell.
  7. I guess I should have clarified that I was referring to speedlites. Monolights generally have much longer durations as you have seen.
  8. You would also need to modify the camera since X sync happens when the first shutter fully opens and you would need light before that point was reached because the second shutter is close behind with faster shutter speeds.
    FP sync is set by the flash unit telling the camera what to do rather than a manual camera setting ? Or have I got that wrong :-( Otherwise we could do all sorts of tricks with ordinary flash units [speedlites].
  9. You would also need to modify the camera since X sync happens when the first shutter fully opens and you would need light before that point was reached because the second shutter is close behind with faster shutter speeds.​
    This is your answer. With focal plane shutters and dedicated speedlights using HSS/FP sync up to 1/8000 sync isnt an issue. But if you are talking about studio lights (monolights and packs) things get really tricky.? With leaf shutter cameras you can shoot past 1/1000 sec sync with studio strobes. ??What you need is a slow or delayed sync similiar to what was used with old school 1970s m-series camera syncs and class m-series flash bulbs for a slow sync delay (because it took about 20-25 milliseconds to reach illumination with these old flash bulbs). Today we use Pocketwizards with Hypersync for an advanced time sync.
    You need these things to sync above 1/250 sec with focal plane shutter cameras and studio strobes:
    Pocketwizards (camera must have a Pocketwizard MiniTT1 or FlexTT5) using Hypersync with the peak or tail method
    The correct camera AND studio strobe combo.
    A studio strobe light with a SLOW flash duration
    According to Pocketwizard, sensor size and flash duration are the two biggest factors in how well Hypersync will work. You can get a very clean sync without clipping well past the 1/250 sync mark. How much more? Depends on your strobe and camera combo. You can get anywhere from 1/320 -1/8000. It is not easy to get the 1/8000 sync and factors depend with certain camera, strobe combo and ambient light. Good studio strobes to use with Pocketwizard Hypersync are: Profoto, Dynalite and Elinchrom with slower "S" head flash duration. I shoot with the Bowens Explorer 1500 strobe pack which has extremely high flash durations but doesnt have any slow flash durations for Hypersync to work well:1500w/s = 1/4,170s, 1000w/s = 1/5,700s 32w/s = 1/3,380s. The slowest flash duration I have on my pack is 1/3,380s.
    A lot of posts on the topic so you can read more here:
  10. Speedlights work OK at full power without being in HSS or FP mode. Their durations are nowhere near as short as they're made out to be. Bowens 6K packs work pretty well too and sync to 1/8000s along with the Bowens Traveller G series packs and 750 Pro monolights :) No PW's required.. you just trick the camera to sync when the front curtain starts to open and you can even signal this with a slave cell.
  11. Ian, in order to "trick" the camera you need to use a FP/HSS speedlight for "high-speed sync hack" when used with studio/monolight strobes. Can you elaborate to everyone in a bit more detail how you are tricking the camera to get 1/8000s sync with the Bowens 6K Quadmatics?
    When it comes to going past 1/250 sync with studio strobes you need PWs or FP/HSS speedlights or both in some form. I have seen successful lighting set ups work with studio strobes and with a FP/HSS speedlight...
    But that isnt really a bad thing... I could throw in a HSS speedlight, and/or a minitt1/flex and daisychain studio strobe packs. Daisychain my Bowens Explorer to Bowens Quads or speedlight or just use the optic slave on the pack...hmmm might actually work. :)
    Anyway I think we answered the OP's question!
  12. As long as the camera provides the sync point at/slightly before the first curtain starts to open then all that remains is using a flash with a suitably long duration.
    I use Nikon so doing this is pretty easy, the simplest way to shoot this way is to set a speedlight on your hotshoe set to FP mode and low manual output and use the in-built slaves on the power packs. As soon as the power packs see the first flash - they sync. There tends to be a slight reduction in maximum output doing this compared to radio, but it does work quite well.
    Using this same method, add a radio transmitter to your camera using the camera PC or flash PC socket for sync to enable your radio, and a receiver to the pack.
    You don't NEED a speedlight in the hotshoe, a radio in the hotshoe which signals the camera that a TTL device is present will make the camera automatically switch sync. I do this with the Quantum FreeXwire D adapter (TTL hotshoe adapter) connected to a transmitter. This then, triggers the remotes.
    Another way, as I use Quantum, I use the Trio on camera and use it's inbuilt radio to trigger remote Quantum's which I set to full output.. 160ws, 200ws, 400ws. Doing this, there is no HSS/FP loss if the flash duration is appropriate - in fact, you can get an increase in relative output at higher shutterspeeds - which - apart from the capability of using wider apertures if you wish, is the only real benefit.
    I just posted in this thread some samples:
    And I did a blog post a while back here:
    FP mode and HSS - exceeding flash sync with no loss in output.
  13. "FP sync is set by the flash unit telling the camera what to do rather than a manual camera setting ? Or have I got that wrong :-(" -
    Since there is a ? mark here, - so this must be a question.
    Just to clarify. There are 2 FP modes in the flash. One is automatic CLS FP mode, where the camera sets up everything, and flash tells nothing to the camera, except possible compensation set on the flash or power fraction value, and the flash just obeys the orders, The other FP mode is also CLS manual mode where you have freedom to set power fraction on the flash for intersity/duration of each flash in the series.
    It is the camera smarts that properly programs FP mode for the flash, taking on account camera ISO, aperture, flash compensation, programs duration and frequency, or total number of consecutive adjucent flashes, and their duration driven by power ratio in manual mode, or determined automatically by the camera.
    First you need to select an "1/250 FP, or ""1/320 FP" shutter speed in the Nikon DLSR camera. This actually will set the flash FP mode. Setting FP mode on the flash without setting the FP in the camera will not cause the FP operation.
    This will program to flash into the FP mode, with current and ever changing camera parameters, e.g. Auto ISO, auto aperture or auto shutter speed, depending on camera mode and lighting conditions.
    If shutter speed drops to 1/250 or slower, possibly caused by the camera needs/mode, then the flash will operate in normal iTTL (not FP) mode.
    WIth multiple external remote CLS fashes working in the CLS/FP mode there is a lot more for the camera to take care of, during preflash testing...
    The subject seems to be complicated, a number of books were already published, on the Nikon CLS flash system alone.

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