Understanding Flash Sync

Discussion in 'Beyond the Basics' started by Restomage, Dec 23, 2009.

  1. Restomage

    Restomage No longer a newbie, moving up!

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    Hey everyone I have a slight problem I'd like some help with. I haven't done any recently, but a couple of months ago I did a photoshoot with a model I know at the beach during sunset but the photos didn't exactly turn out the way I wanted them to. I think i've figured out my problem now but at the time I was using a SB-600 as my main light.

    At full flash power, the photos either came out underexposed:

    [​IMG]

    or I'd get only half the subject lit:

    [​IMG]

    My goal was to get the subject exposed properly and the background underexposed but as you can see I didn't achieve either. I'm using a D90 and the flash sync speed on it is 1/200s, and I was shooting these pictures at 1/400s and 1/320s with an f stop of f3.5 which I think is my problem. Since my flash sync speed is 1/200s that means the maximum shutter I can shoot at is 1/200 right? And I have to underexpose the background by adjusting the aperture correct?

    Thanks.
     
  2. sdowden

    sdowden TPF Noob!

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    underex the background by making the aperture smaller
     
  3. Derrel

    Derrel Mr. Rain Cloud

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    You can control the background brightness by keeping the ISO low, and also by adding neutral density filtration over the lens. In situations like like you were shooting in, later in the day, neutral density filtration over the lens is advantageous because you can drop three stops of background brightness quite easily, while at the same time, you need only fractional flash power, so the loss of *effective* flash power due to the neutral density filtration over the lens is not a detrimental loss.

    And yes, you can't go above 1/200 second unless High Speed Sync mode is in use. Some cameras call this FP sync; when using High Speed Synch, the flash will emit a very rapid series of pulses which together, will allow the shutter to be raised well above the 1/200 second limit.
     
  4. Garbz

    Garbz No longer a newbie, moving up!

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    That surely doesn't qualify as a bikini.

    /EDIT: Just realised FP sync isn't the issue. Both pictures already have shutter speeds that put it in FP sync territory, yet they both exhibit different behaviours.

    [disregard this crap below]

    As Derrel mentioned FP sync is the key here. However your ability to use it will depend on how you're triggering the flashes. I believe that the only way to get wireless FP sync is to use a proper i-TTL wireless trigger. That means no cactus triggers, pocket wizards, or no inbuilt camera flashes for the commander. Providing the SB-600 plays along I think your solution may be to use your SB-800 on camera as the wireless master. I am not entirely sure about that though.
     
  5. STOFFEL

    STOFFEL TPF Noob!

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    Okay, after much researched and done, I have not found a solution that makes me happy, on the look and action of a Wireless remote shutter and speed firing solution for High Speed Flash Sync shooting up to 1/8000, for the Sony a900, as I have been doing with the Canon 1D III, so unfortunately for now I will have to pass on the Sony.

    I will be doing a short Video commercial for Sony with the a850 or a900 early January with multi flash, will see if the new year brings new solutions, but to my understanding Sony has no intention to go after the Pro shooters, and for this I don't think that we will see a valuable solution soon, Canon here I return t you, and you better bring the 1D IV free of Focus issues
     
  6. Mike_E

    Mike_E No longer a newbie, moving up!

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    The two problems that I see are that what you are trying to accomplish is Fill flash and your flash's color temp is wrong for the time of day.

    For fill flash it is OK in a lot of situations to have the flash on camera (what you are worried about here is seeing the flash shadow mainly). ((edit: you do need to remember that you will be shooting with a negative flash comp to just bring the subject out of shadow) The object of course is to bring up the subject's exposure while retaining the natural mood of the background. I'm not going to tell you how to do it because there is a LOT more to it than a couple of paragraphs worth so you would be much better served by doing the research yourself. Also see "dragging the shutter" (article 4 on the right would be a good place to start ;) http://www.planetneil.com/tangents/ )

    The second subject is one where you'll need to read up on for yourself as well. Look up gelling your flash. How to gel is easy it's the part about color matching and where to find the gels that get's tricky.

    Good Luck,

    mike




    and get that girl some clothes, you wouldn't want her to get a chill :lol:
     
    Last edited: Dec 24, 2009

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