Lighting/Sync Help

Discussion in 'Beyond the Basics' started by DigitalFelon, Sep 23, 2015.

  1. DigitalFelon

    DigitalFelon TPF Noob!

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    Hello fellow Photographers,

    I've been in the photography game for a while now, but I have recently decided to step into the off camera flash scheme. I'm having a issue trying to figure out how to control the power on the canon 580 ex II flash while its off camera. Let me give you a quick run down on my equipment so you get a better understanding of what Im trying to achieve.

    Camera: Canon 7D
    Triggers: Pocket Wizards III
    Light Meter: Sekonic
    Flash: Canon 580 EX II

    OK, so here is what Im trying to do.

    One PW goes on the camera, the other sync'd on the flash.
    Essentially, I will set the camera to AV mode and figure out the ambient light the camera is reading. Lets say F4 @ 1/60th. Once this is figured out, I will know what to match my flash power to by using the light meter to pair the reading from the camera with the off camera flash. From here, I can adjust the shutter on the camera to achieve the look I want (darker background, etc). I know this stuff pretty well... The problem I'm having is when the 580 EX II is on the light stand, how can I adjust the power to where I want it? Do I simply put it on Manual mode, and guess what power to shoot at based on what the light meter is reading?

    Any help is appreciated guys, thanks!


     
  2. JacaRanda

    JacaRanda Hobbyist Birdographer

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    I believe the answer to your question is yes. Use manual to adjust the power. Otherwise, you would adjust using ETTL.

    Hoping I have that correct.
     
  3. Dave442

    Dave442 Been spending a lot of time on here!

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    With digital it seems easiest to set the flash to something you know should be close and then adjust based on the light meter camera screen.

    You can also use your flash guide number and calculate a power setting to start with.

    Might as well go ahead and give it a try using both Manual and ETTL for the flash exposure control.
     
  4. Derrel

    Derrel Mr. Rain Cloud

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    I do most of my flash work with manual power settings, and go based on experience, and what I want. Do you want a what is referred to as a full flash shot, or a flash-as-main-light type of exposure, one in which the flash's output makes up the majority of, or all of, the exposure? If so, and the distance is longer, then you're probably in full flash power setting territory; if the flash is very close to the subject, the needed flash power might be as little as 1/128 power.

    For fill-flash, where the role of the flash is just to lighten up shadows, or to add a bit of eye sparkle, then it's likely that a significantly lower amount of manual flash output should be selected. Fill flash tends to look best at Minus 1.0 EV to as much as Minus 2.7 EV, so there's a good deal of latitude in "how much" flash needs to be fired to achieve the desired exposure and the desired look.

    I typically use the manual flash power adjustment buttons on the back of my flash; I often find that 1/4 to 1/16 power is the right amount of fill-flash for me outdoors when using the Nikon SB 800 and a 1-meter pigtail off-camera flash connecting cable.
     
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  5. Alexr25

    Alexr25 No longer a newbie, moving up!

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    PW Plus III triggers do not handle E-TTL communication between camera and flash so you will have put both the flash and the camera into manual mode and manually adjust the flash power. If you want to use PocketWizards for off-camera E-TTL you need the PW Min TT1 and/or the PW Flex TT5.
    You don't say what model Sekonic meter you have but if it can't measure flash exposure then you will have to adjust the flash by trial and error.
     
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  6. Vtec44

    Vtec44 Been spending a lot of time on here!

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    1. You can put it in manual and compensate 2. You can use exposure compensation in AV mode and adjust the exposure to compensate for the flash power, but you can't control flash and ambient separately this way. 3. If you're shooting a live event where people are moving, try using inverse square to determine the best spot to put your flash.
     
  7. Jasii

    Jasii No longer a newbie, moving up!

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    needs elucidation please?
    Rgds,
     
  8. Alexr25

    Alexr25 No longer a newbie, moving up!

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    It's a fancy way of saying move the flash away to reduce the amount of light (double flash to subject distance = 2 stops less illumination) but it all boils down to if your meter can't measure flash then you have to resort to trial and error.
     
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  9. Vtec44

    Vtec44 Been spending a lot of time on here!

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    At a certain distance, around 4-8ft if I remember it correctly, the light drop off won't noticeably affect exposure. So you have more room for errors.
     
  10. Jasii

    Jasii No longer a newbie, moving up!

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    Thank you Alex, James for the revertal.
    Appreciate it.
    Jasii
     
  11. Derrel

    Derrel Mr. Rain Cloud

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    OLD flash: Vivitar 285 HV, Guide Number at 100 ISO is 110 in Feet, at normal beam spread.

    110 divided by 3 equals f/36.66

    110 divided by 3.5 f/31.42

    110 divided by 4 f/27.5

    110 divided by 4.5 equals f/24.44

    110 divided by 5 equals f/22

    110 divided by 5.5 equals f/20

    110 divided by 6 equals f/18.33

    110 divided by 7 equals f/15.71

    110 divided by 8 equals f/13.71

    110 divided by 9 equals f/12.22
    110 divided by 10 equals f/11
    110 divided by 11 equals f/10

    110 divided by 12 equals f/9.16
    110 divided by 13 equals f/8.46
    110 divided by 14 equals f/7.85
    110 divided by 15 equals f/7.33
     
  12. TCampbell

    TCampbell Been spending a lot of time on here!

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    The short answer to your question is: Yes... you put the 580EX II in manual mode and adjust the power level.

    You don't mention which Sekonic meter you own, the high end meters calculate something called "flash contribution" which means they meter the ambient light and they also meter the burst of flash. Then they report how much light (as a percentage) is coming from the flash. For example, if I'm taking a portrait in the sun and I want my flash to be a "fill" flash, then I want to make sure there is more sunlight (that's my "key" light) then "flash". If they are at 50/50 (flash contribution is 50%) then it means the amount of light hitting the subject from the flash is exactly equal to the amount from the sun. That would eliminate shadows and you probably WANT shadows because they help provide some dimensionality to the image (you just don't want harsh shadows.) To get "weak" shadows you might cut the flash power by half. That would a 2:1 relationship where there's twice as much light from the sun as compared to the flash (flash contribution would be at 33% -- or close to it.) But note how you're using the meter to read "flash contribution" and just manually adjusting the power on the flash.

    Another way to adjust power from the flash is change the distance between the flash and the subject. The farther the light source, the more the light spreads out. Think of water hose with a spray nozzle on it set for a wide spray pattern. If you stand 1' away from the end of the the hose, probably ALL of the water is going to hit you and you'll be soaked. But if you are 20' away from the spray nozzle, the water is spreading out so much that most of the water actually misses you and it will take longer to get wet. Light works similarly... it spreads out meaning that less of that light actually hits your subject because more of it misses the subject (it had a chance to spread out more.)

    The relationship is called the "inverse-square law" because it turns out the relationship is based on the square root of 2 (√2 = 1.414.. but you can round to just "1.4"). If your flash is 5' away from a subject and some amount of light is reaching your subject which you think is too bright, multiple your distance by 1.4 (so 5 x 1.4 = 7). If you move the flash to that new distance (7') your flash will now provide EXACTLY HALF as much light.

    To answer the question you didn't ask: Your 7D and 580EX II can actually communicate directly and you don't need the PocketWizards.

    The 7D has the ability to be a flash commander. See: Canon DLC: Blog Post: Easy built-in off-camera flash control with the EOS 7D

    The 580EX II will need to be in "slave" mode and using E-TTL. Also, the 580EX II requires direct line-of-sight to the flash on the camera. In a confined area (inside shooting with a room that isn't too big) the 580EX II will likely trigger regardless of where the 580EX II is pointed. But in a large open space or outside the 580EX II needs to have it's sensor (which is in the lower half of the unit -- it's that red-lens you see on the front) pointed at the camera flash. Since the flash head on the 580EX II can tilt & swivel, you can still direct the flash head in any direction you want.
     

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