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Thread: Help !! How to use external flash to render accurate colours-white balance

  1. #1

    Default Help !! How to use external flash to render accurate colours-white balance

    Hi hi

    Need some pointers from experienced Flash users.

    Just got a 3rd party flash and tried it a few times. However there are a few issues with the camera with light metering and outdoor shots.

    1) Usually when without flash, would adjust the settings (Shutter speed or Aperture) using the light meter in viewfinder as a guide. However, when using the external flash this cannot be done, meter could be -1 or -2 but would be properly exposed once the external flash is used.

    Question : Is this normal? or is it because I am using a 3rd party flash and not an original canon flash like 430ex or 580ex ?

    2) For indoor shots, for boucing off white low ceiling (without diffuser) with Auto White Balance, the shot turned out alright with skin colours properly exposed.

    For outdoor shots (took a shot of Xmas trees & lightings at orchard) , when I take a photo without flash on AWB the colours were rendered correctly.

    When I took use the external flash with a DIY White Matt bounce card, the person is exposed properly and colours reproduced correctly but the background lights turned very 'Yellow", a yellow tint.
    If I change the White Balance to "flash" the person will turn out to be "bluish" or overexposed but the colours of the lightings will be reproduced accurately.

    Question : Is it due to insufficient or inappropriate boucing of lights cos indoor shots with boucing this problem does not exist. If a proper diffuser with a yellow filter is used, will the white balance for the person and the background lights BOTH be rendered accurately ?


    Without Flash


    With Flash



    Sorry long post.

  2. #2
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    Default Re: Help !! How to use external flash to render accurate colours-white balance

    Quote Originally Posted by Justintime View Post
    Hi hi

    Need some pointers from experienced Flash users.

    Just got a 3rd party flash and tried it a few times. However there are a few issues with the camera with light metering and outdoor shots.

    1) Usually when without flash, would adjust the settings (Shutter speed or Aperture) using the light meter in viewfinder as a guide. However, when using the external flash this cannot be done, meter could be -1 or -2 but would be properly exposed once the external flash is used.

    Question : Is this normal? or is it because I am using a 3rd party flash and not an original canon flash like 430ex or 580ex ?

    2) For indoor shots, for boucing off white low ceiling (without diffuser) with Auto White Balance, the shot turned out alright with skin colours properly exposed.

    For outdoor shots (took a shot of Xmas trees & lightings at orchard) , when I take a photo without flash on AWB the colours were rendered correctly.

    When I took use the external flash with a DIY White Matt bounce card, the person is exposed properly and colours reproduced correctly but the background lights turned very 'Yellow", a yellow tint.
    If I change the White Balance to "flash" the person will turn out to be "bluish" or overexposed but the colours of the lightings will be reproduced accurately.

    Question : Is it due to insufficient or inappropriate boucing of lights cos indoor shots with boucing this problem does not exist. If a proper diffuser with a yellow filter is used, will the white balance for the person and the background lights BOTH be rendered accurately ?


    Without Flash


    With Flash



    Sorry long post.
    Ok quick tip on using flash. You should use your camera's in-built meter to measure the correct exposure for the background that you want, and the flash can take care of the correct exposure of the person in the foreground.

    Next, you have to understand that your flash is never going to be able to provide light to your background in a night scene, especially when it is so far away! You'd need floodlights for that

    So if you think along those lines, you will understand that all the colours you see for your background is coming not from your flash, but from the ambient lighting from the christmas tree and the street lamps. So, the longer your shutter is open, the more yellow your photo is going to be in the background.

    Next, your flash output is not as yellow as the background. Since your flash is not able to illuminate the background, there is no way to avoid the background being yellow without adjusting the white balance. In the first pic without flash, your camera uses the auto white balance to compensate for the whole photo based on the yellow lights, hence the final pic is less yellow.

    In the second pic, flash is used, so the camera's white balance is set to ensure that the flash output is properly colour balanced, at the expense of the background. If the camera were to use the same white balance logic as the first pic, then you would end up with the person in the foreground looking like a blue smurf in order to make the background less yellow, since adding blue will tone down the yellow. I think what you described in your question matches what I am saying.

    So the conclusion is that mixed lighting will always have this problem. The camera will have to choose one of the lighting types to white balance, and it will always affect the other lighting type.

    Hope this helps.

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    Default Re: Help !! How to use external flash to render accurate colours-white balance

    Oh yah, in reply to your question 1, yes this is normal. Any exposure setting you are setting when using flash will normally only affect the parts of the photo that are not affected by the flash. To test this out, you can try to set your shutter speed to something like 1/1000 and aperture to something like f/11 or f/16 in your example above. You will notice that the result is that the person in the foreground is still exposed correctly, but the christmas tree probably will be very dark or maybe not even visible anymore.

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    Default Re: Help !! How to use external flash to render accurate colours-white balance

    Correct me if I am wrong. In this case, I think it call for a CTO gel to balance out the white balance to get the same overall lighting. So the white balance would only need to compensate for tungsten colour.
    EOS 5DMkiii|17-40F4L|24-105f4L|70-200f4L IS|50f1.4|85f1.8|580EX II

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    Default Re: Help !! How to use external flash to render accurate colours-white balance

    Quote Originally Posted by plato View Post
    Ok quick tip on using flash. You should use your camera's in-built meter to measure the correct exposure for the background that you want, and the flash can take care of the correct exposure of the person in the foreground.
    I'm curious on how to do this?
    Use spot metering to determine correct exposure for background and shift to subject after locking AE or use evaluative metering pointed at subject and just adjust for proper exposure?
    Thanks!

  6. #6

    Default Re: Help !! How to use external flash to render accurate colours-white balance

    Hi hi

    Wow thank guys! This really helped a lot. Guess Clubsnap really is a good place to learn

    For 1) I am relieved that it is not because I used a 3rd party lens and it is not compatiable, cos feel it is really a value for money flash.

    Btw got quizzed on the flash model so thought better post it here to share, bot it at $190 from MS color (discount after cash payment). Guess itís a budget flash for newbies like me who want to learn flash photography and dun want to fork out more than double for 430 or 580 original canon flashes

    Btw loved the indoor effect bounced from ceiling so much better than the blurred images from before using high ISO plus F2.8 or the harsh inbuilt flash.

    For 2) Thanks for the suggestion of the CTO gel. Was thinking of similar stuffs.


    Question again : Saw that some flash diffusers have yellow/warming filters perhaps this will balance out the blue smurf effect of the person in the foreground aka cancel out the mixed lighting problem ??

    Thinking of using yellow bounce card or get something like the lightsphere with yellow cap ?

    Think these will work ?

  7. #7
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    Default Re: Help !! How to use external flash to render accurate colours-white balance

    Quote Originally Posted by Justintime View Post
    Hi hi

    Wow thank guys! This really helped a lot. Guess Clubsnap really is a good place to learn

    For 1) I am relieved that it is not because I used a 3rd party lens and it is not compatiable, cos feel it is really a value for money flash.

    Btw got quizzed on the flash model so thought better post it here to share, bot it at $190 from MS color (discount after cash payment). Guess itís a budget flash for newbies like me who want to learn flash photography and dun want to fork out more than double for 430 or 580 original canon flashes

    Btw loved the indoor effect bounced from ceiling so much better than the blurred images from before using high ISO plus F2.8 or the harsh inbuilt flash.

    For 2) Thanks for the suggestion of the CTO gel. Was thinking of similar stuffs.


    Question again : Saw that some flash diffusers have yellow/warming filters perhaps this will balance out the blue smurf effect of the person in the foreground aka cancel out the mixed lighting problem ??

    Thinking of using yellow bounce card or get something like the lightsphere with yellow cap ?

    Think these will work ?
    I think any of the options you asked about should help, eg the CTO gel, bounce card or flash diffuser with warming filters.

  8. #8
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    Default Re: Help !! How to use external flash to render accurate colours-white balance

    Quote Originally Posted by ramian View Post
    I'm curious on how to do this?
    Use spot metering to determine correct exposure for background and shift to subject after locking AE or use evaluative metering pointed at subject and just adjust for proper exposure?
    Thanks!
    Yes, if you are not using Manual mode, then you will need to lock the exposure for the background. You can use any metering mode you want. However, there is no point metering on the subject since the flash is going to take care of the exposure for the subject. But of course this is just general advice. If the subject is too near or wearing black, the flash may still get the exposure wrong and over expose the foreground subject. For that, you will need to use flash exposure compensation to deal with this, or else use the flash on manual exposure mode too.

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    Default Re: Help !! How to use external flash to render accurate colours-white balance

    Quote Originally Posted by plato View Post
    Yes, if you are not using Manual mode, then you will need to lock the exposure for the background. You can use any metering mode you want. However, there is no point metering on the subject since the flash is going to take care of the exposure for the subject. But of course this is just general advice. If the subject is too near or wearing black, the flash may still get the exposure wrong and over expose the foreground subject. For that, you will need to use flash exposure compensation to deal with this, or else use the flash on manual exposure mode too.
    I wonder how to lock (background)exposure when your flash is on
    Doesn't it engage FEL mode and fire a preflash when you press the AEL button?

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