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Thread: Flash technique - Dark background..pls help

  1. #21

    Default Re: Flash technique - Dark background..pls help

    Ahh..... My bad. I have failed to see that i missed a word. Max Aperture does not matter. Was being kua zhang to put F22.

    I used F22 is to let the TS know that even if you shoot at F22, with the flash power set to required for F22, ISO of camera and distance of flash to subject, the subject will be correctly exposed. What add the ambient light in is the shutter speed.

    Hence, I stated:
    Aperture affects flash light capture in the camera
    Shutter speed affects the ambient lights capture.
    ISO affects both if not wrong.

    Quote Originally Posted by daredevil123 View Post
    ISO, Aperture and Shutter speed together determines your exposure. So Aperture do matter. If your aperture is smaller, you will need a longer shutter speed to get the same exposure (be it the subject or the ambient lights behind).
    I agree if this is shooting without flash.


    Quote Originally Posted by daredevil123 View Post
    The reason behind a dark background when using flash (TS's problem) is that while the subject is lighted well by the flash, the exposure did not allow for the background to expose correctly. In this situation, if the flash power is fixed (not TTL because TTL is always varying flash power) and keeping the subject in correct exposure, no matter which combination of aperture/shutter speed will have no bearing on getting the background into exposure. The only thing you can do is to lower the flash power. This means, the key is to balance the amount of light from the flash against the ambient light. And once you lower the flash to balance the ambient light in a dark situation, you will need to boost the exposure. How can you boost exposure? 3 ways: 1. up your ISO, 2. longer shutter speed, 3. Larger aperture. We usually leave aperture alone if we want to maintain the same DoF.
    I do not really agree on this.

    - With the flash power fixed and aperture fixed as the subject is correctly exposed. What you can do it what we call drag the shutter. The flash power has already gone. There is no more flash even if you keep the shutter on for another 1sec after it has been fired. Keeping the shutter open will allow the ambient light to flow in.




    Quote Originally Posted by daredevil123 View Post
    Edited.

    My bad, I stand corrected. EV is just a override to the exposure metering.

    So, if you set EV -1 and FV +1, logic says your subject should be similar lighted, but your background will be a lot darker than EV and FV at 0. But if you are using TTL, it is another story, as there is another calculation done by the camera in TTL.
    Indeed that the BG will be slightly, not very unexposed. This is actually how you get a more saturated colour of the background. This does not matter whether it is TTL or not. As for this case, the flash is only used for lighting up the subject. Not the room. This will work even if you are shooting outdoor.


    Quote Originally Posted by wildsoyabean View Post
    wrong . aperture matters.
    e.g shooting at f1.2 with flash at 1/250s 50mm will probably over expose everything,
    shoot at f11 with flash @ 1/250 might be just nice. this is just an example. the actual correct exposure will have to depend on the amount of ambient light available
    Stating Fstop with no ISO and flash GN does not tell me it will be correctly exposed.

    ok. let's have this config.

    F1.2
    1/250s
    ISO 100
    12mm to 1000mm lens whichever focal length you choose.
    flash placed at 20m away from subject GN 24. Based on formula, aperture*distance=GN
    The subject should be correctly exposed. Hope my calculation is correct. Never tried shooting with GN. damn.
    If it is night time, you might night get much ambient light in. You need to drag the shutter to get more ambient light in. Not by increasing power of your flash. Your subject will end up overblown. Correct me if any incorrect info given.

    Thanx

  2. #22

    Default Re: Flash technique - Dark background..pls help

    Quote Originally Posted by daredevil123 View Post
    You need to know what a bounce card is for. You see, when using a bounce card, we usually bounce the light off the ceiling, and most of the light is actually coming from the bounce off the ceiling. When bouncing off ceiling, you get shadows in eye sockets of your subjects (aka raccoon eyes). The bounce card is intended to send some light forward to fill in.

    Diffuser can work well depending on how you use it. Which one are you using now?
    Thanks. I'll try make my own bounce card.
    Currently I'm using this one http://www.mennon-usa.com/store/inde...roducts_id=289

  3. #23
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    Default Re: Flash technique - Dark background..pls help

    Quote Originally Posted by peterlimyk View Post
    Thanks. I'll try make my own bounce card.
    Currently I'm using this one http://www.mennon-usa.com/store/inde...roducts_id=289
    Oh ok, the cap type. You can try to vary the angle of your flash head.

    As for bounce card, you can start off by using a white business card and some rubber bands. You can try other bigger cards if you feel the business card is too small.

  4. #24
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    Default Re: Flash technique - Dark background..pls help

    Quote Originally Posted by Richter View Post
    With the flash power fixed and aperture fixed as the subject is correctly exposed. What you can do it what we call drag the shutter. The flash power has already gone. There is no more flash even if you keep the shutter on for another 1sec after it has been fired. Keeping the shutter open will allow the ambient light to flow in.
    I stand corrected. As flash is a very quick flash of light.

    But aperture matters for background also. If the aperture is smaller you need to drag longer. If the shutter is dragged too long, the background light may be susceptible to blur from motion either from background objects/people or handshake.

    In modern day usage, with TTL, flash power is varied by the TTL system to compensate for the aperture.

  5. #25

    Default Re: Flash technique - Dark background..pls help

    Quote Originally Posted by daredevil123 View Post
    I stand corrected. As flash is a very quick flash of light.

    But aperture matters for background also. If the aperture is smaller you need to drag longer. If the shutter is dragged too long, the background light may be susceptible to blur from motion either from background objects/people or handshake.

    In modern day usage, with TTL, flash power is varied by the TTL system to compensate for the aperture.
    I agree fully.

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