Flash question E-TTL

Discussion in 'Photography Beginners' Forum' started by Robin Usagani, Sep 14, 2010.

  1. Robin Usagani

    Robin Usagani Been spending a lot of time on here!

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    I have several questions for you guys. I think I am still confused with how to use my flash properly. I have 550 ex. Here are my questions and please correct me if my assumption/understanding is wrong:

    1. If I am not mistaken, E-TTL uses a preflash that will calculate how much power the flash needs to light up the subject properly. That means even if I put filter on my lens, or put diffuser on my flash, it will not matter correct? Since it shoots a preflash, I assume it uses more battery power. HOw do I know what kind of power the shot in ETTL mode was taken? If I am shooting on a tripod on a subject that is always the same distance, I want to be able to just change the flash to manual and copy the ETTL so that I dont shoot preflash and use up the battery power.

    2. If I set the flash to high synch, how much power does the flash put out? I assume it doesnt do preflash anymore?

    Thanks for your help guys!
     
  2. Village Idiot

    Village Idiot No longer a newbie, moving up!

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    From what I know, you can't find out what the flash output was for the TTL shot. This is where either a light meter, knowing your guide numbers, or just plain old experience kicks in to save the day.

    The only reason I personally use TTL is when I have a camera on flash and I'm shooting in a dynamic lighting environment. Other than that, it's purely manual off camera flash for me. With enough time, you'll know that at f/5.6 and ISO 100, your flash should be at a certain power for the given distance or whatever example settings you want to use.

    3. How ever much it needs to for the shot? I assume you're talking TTL. It would have to preflash to find out the proper exposure level. It's that in HSS mode, it acts as a strobe and does multiple flashes, this will kill batteries and reduce it's overall effectiveness, but if you need it, you need it.
     
  3. Robin Usagani

    Robin Usagani Been spending a lot of time on here!

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    I turn the high synch on when I am shoooting in the sun when I need fill flash. Because if I use other mode it will only go up to 1/200 sec shutter. Shall I use something else?
     
  4. Village Idiot

    Village Idiot No longer a newbie, moving up!

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    You could try narrowing your aperture. It'll give you a larger DOF though, and that may not be wanted. Using a ND filter will kill the sun and allow you to use a wide aperture but require you to use higher flash powers.

    You could also buy a Nikon D70 which pretty much has an unlimited sync speed due to using an electronic shutter on top of a mechanical one.

    Edit: You could also push you shutter speed. Canon's shutter speed on the 500D should be 1/250 with Canon speedlights. You cand push it faster. Eventually, you'll have the black bar from the shutter creeping across your exposure, but at that point either go with a slow enough shutter speed that you can use or shoot a portion of the frame where you can crop the bar out.

    There's also something like the new Pocket Wizard radio triggers that let you adjust the timing on how they fire so that you can get your flashes to properly sync at higher speeds than the camera's specified x sync.
     
  5. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    That's correct. E-TTL...as in Through The Lens. So no matter what you have on your flash, on your lens or how you may be bouncing the flash...it reads the light coming back into the lens.

    The preflash isn't a powerful burst, it's rather small. So I wouldn't be too worried about it using up your battery power. If you are worries about the life of your batteries, use a larger aperture or a higher ISO.

    No, it still preflashes when in HSS mode. (it still has to meter)...but the difference is that in HSS mode, it pulses the flash rather than firing in one big burst. This reduces the flash range and uses up the batteries faster.

    It's a toss up decision as to whether you want to use HSS or just use a smaller aperture, when trying to control bright sunlight. Using a smaller aperture (without HSS) will require more flash power and eventually limit your range once you reach full power.
     
  6. Robin Usagani

    Robin Usagani Been spending a lot of time on here!

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    Wow thanks BigMike. You are my favorite member here! You always help me a lot. Even when I ask silly questions. I am really thankful for that. My next question is, why cant I use manual mode on the flash and go with faster shutter speed like the HSS?
     
  7. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    I'm not sure if HSS requires you to be in E-TTL mode.

    I'm not sure if this is what you are asking, but the reason that you can't use higher shutter speeds (when not in HSS) is because of the way the shutter works. It consists of two curtains. At the start, they are both in the same position, top of the frame. Because the lower curtain is fixed at the bottom, it's covering the sensor (shutter is closed).
    When you fire the camera, the lower curtain goes down (shutter open) and the top curtain follows it (shutter closed) after a set amount of time (the shutter speed).
    So for a certain amount of time, both curtains are fully open, and this is when the flash fires and illuminates the whole sensor.
    But when the shutter speeds gets faster, the upper curtain has to start following the lower curtain before the lower one is fully open. At 1/8000, the top curtain is following the lower one very closely. So if you fired the flash during the exposure, it would only illuminate a 'slit' across the frame because the shutter is never fully open at those speeds. That's why our cameras have a 'max sync speed'. That's the fastest speed at which the shutter is fully open.

    What HSS does, is pulse the flash repeatedly, rather than dumping it all in one burst. So with multiple flashes, it can cover the whole frame as the slit between the shutter curtains moves across the frame.
     

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