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Thread: question on flash, underexposure

  1. #1
    Member kwanhan's Avatar
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    Default question on flash, underexposure

    Hi I've got a question on using an external hotshoe flash (i just bought the nissin di622) and a resulting underexposed image.

    Have done a quick search and have read through ChenGuy's recent thread on flash and the replies on settings and metering....

    Been testing out the flash with different settings and bounce angles... one issue is that I realized that my flash consistently underexposes by a lot when i point it directly at the subject (90 degrees), whereas at the same distance and settings and metering, bounced shots off the ceiling turned out fine. (all shots using TTL, and i'm using d5000, didn't touch EV or FEV)

    Can anyone help explain why this is so?

    (Will post images if necessary)

    I imagined that a directly pointed flash would result in a brighter image? Was there some sort of compensation mechanism working?

    Thanks!

  2. #2

    Default Re: question on flash, underexposure

    Quote Originally Posted by kwanhan View Post
    Hi I've got a question on using an external hotshoe flash (i just bought the nissin di622) and a resulting underexposed image.

    Have done a quick search and have read through ChenGuy's recent thread on flash and the replies on settings and metering....

    Been testing out the flash with different settings and bounce angles... one issue is that I realized that my flash consistently underexposes by a lot when i point it directly at the subject (90 degrees), whereas at the same distance and settings and metering, bounced shots off the ceiling turned out fine. (all shots using TTL, and i'm using d5000, didn't touch EV or FEV)

    Can anyone help explain why this is so?

    (Will post images if necessary)

    I imagined that a directly pointed flash would result in a brighter image? Was there some sort of compensation mechanism working?

    Thanks!
    Should be the dynamic range at work...camera purposely underexpose so that you get more detail. Can be fixed in post processing. over exposed on the other hand is more permanent.

    You want to compensate, use the EV controls. most of the time +2/3 is good enough or FEC to "increase" power to the flash.
    You wont see me much less remember me but i am the guy who makes you look good.

  3. #3
    Member kwanhan's Avatar
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    Default Re: question on flash, underexposure

    Quote Originally Posted by Reportage View Post
    Should be the dynamic range at work...camera purposely underexpose so that you get more detail. Can be fixed in post processing. over exposed on the other hand is more permanent.

    You want to compensate, use the EV controls. most of the time +2/3 is good enough or FEC to "increase" power to the flash.

    hmmm so it will always underexpose if its angled at 90 degrees pointed at subject?

    because the image is really really bad, much worse than the pop-up flash... not just underexpose but really jialat vignetting at corners

    think i will try to post an image soon...

    anyone else has any idea what could be wrong?

  4. #4

    Default Re: question on flash, underexposure

    Quote Originally Posted by kwanhan View Post
    hmmm so it will always underexpose if its angled at 90 degrees pointed at subject?

    because the image is really really bad, much worse than the pop-up flash... not just underexpose but really jialat vignetting at corners

    think i will try to post an image soon...

    anyone else has any idea what could be wrong?
    ....not just underexpose but really jialat vignetting at corners

    there are people who spend countless hours in PS to get that effect just right.
    You wont see me much less remember me but i am the guy who makes you look good.

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    Member NeTHaCk's Avatar
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    Default Re: question on flash, underexposure

    Quote Originally Posted by Reportage View Post
    ....not just underexpose but really jialat vignetting at corners

    there are people who spend countless hours in PS to get that effect just right.
    im one of them ?

    why not TS post a picture ?

    when you bounce, the "light" becomes even but when its directional straight .. it's "focused" on object
    Nikon D7000 : Tamron 17-50VC f2.8, SB-900
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  6. #6

    Default Re: question on flash, underexposure

    Quote Originally Posted by kwanhan View Post
    hmmm so it will always underexpose if its angled at 90 degrees pointed at subject?

    because the image is really really bad, much worse than the pop-up flash... not just underexpose but really jialat vignetting at corners

    think i will try to post an image soon...

    anyone else has any idea what could be wrong?
    its subject underexposed or just your background?

    for the vignetting, it's most likely cause by the flash's angle of coverage isn't wide enough for the lens you are using.. not sure if the di622 has a built in wide-angle diffuser but you can try getting those diffuser caps just to spread the light out..

  7. #7

    Default Re: question on flash, underexposure

    Could be a metering issue???
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  8. #8
    Senior Member madmartian's Avatar
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    Default Re: question on flash, underexposure

    Strange things do happen
    Take the shot!

  9. #9
    Member kwanhan's Avatar
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    Default Re: question on flash, underexposure

    Hi all, just did some test shots at the following parameters.

    Camera: D5000
    Lens: 18-70mm DX
    Focal Length: 18mm
    Aperture: 3.5
    Shutter speed: 50
    ISO: 200
    Picture Control: Standard
    Exposure compensation: None
    Flash Exposure compensation: None
    White Balance: Auto
    Image Quality: Fine (then resized for upload)
    Focus Mode: AF-S
    AF-Area Mode: Single point
    Metering: Matrix
    Active D Lighting: Off
    Flash mode: TTL, the in-built diffuser and bounce card not used

    All shots taken on 10 second timer with my camera on a shelf, room light on (don't have tripod and didn't have anyone to help, so some are out of focus. sorry that you have to see me in my 'boh liao' at home look)

    Also my mistake in the terms used- realized that 90 degrees means straight up at the ceiling. What I meant was 0 degrees. Direct at subject.

    Images as follows:

    1) 0 degrees direct at subject


    2) 45 degrees bounced


    3) 60 degrees bounced


    4) 75 degrees bounced


    5) 90 degrees (straight up at ceiling)


    as you can see, the one with flash pointed directly at me is really really underexposed.

    what do you guys think? is that normal?

    Thanks for all the help and suggestions so far!

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    Default Re: question on flash, underexposure

    The extent of vignetting seems rather constant across the photos with the 0 photo demonstrating more severe underexposure relative to the rest. I don't think it's a issue of the flash if the light is being bounced off the ceiling for subsequent photos -- and I am guessing that it may be an effect of the lens (since it's 18 mm @ F3.5 at any rate and it's a DX lens for a Nikon 1.5x crop camera). One way to find out whether this 'guess' is true would be to repeat the shoot at a longer focal length and/or a smaller aperture.

    As for the underexposure, I can think of increasing FEC as a resolution. Increasing by one stop might help, though there should be some slight underexposure after that?
    1D3, EF 16-35mm F2.8L II, EF 24-70mm F2.8L, EF 70-200mm F2.8L IS, Speedlite 580EX II, 420EX

  11. #11
    Member kwanhan's Avatar
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    Default Re: question on flash, underexposure

    Quote Originally Posted by zhuangzhou View Post
    The extent of vignetting seems rather constant across the photos with the 0 photo demonstrating more severe underexposure relative to the rest. I don't think it's a issue of the flash if the light is being bounced off the ceiling for subsequent photos -- and I am guessing that it may be an effect of the lens (since it's 18 mm @ F3.5 at any rate and it's a DX lens for a Nikon 1.5x crop camera). One way to find out whether this 'guess' is true would be to repeat the shoot at a longer focal length and/or a smaller aperture.

    As for the underexposure, I can think of increasing FEC as a resolution. Increasing by one stop might help, though there should be some slight underexposure after that?

    hmmm i don't have any photos to back it up now, but from my tinkering around, i'm quite sure that the underexposure at 0 degrees is repeated at other focal lengths as well (70mm for example)

    my friend was mentioning that he read somewhere that some flashes are designed to flash at full power anywhere other than 0 degrees....

    ....just a bit ma fun to have to dial in FEC for shots with flash at 0 degrees... although i know most of the times for practical usage it would be bounced unless too high ceiling... thought that TTL ought to kick in and balance things for a properly exposed image.. no matter how i angle it

    anyone using the nissin di622 on a Nikon DX body got similar issues?

  12. #12

    Default Re: question on flash, underexposure

    Should be a problem w/ the flash TTL metering..
    Should be over controlling at zero degree in this case..

  13. #13
    Member kwanhan's Avatar
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    Default Re: question on flash, underexposure

    Quote Originally Posted by horizon_grazer View Post
    Should be a problem w/ the flash TTL metering..
    Should be over controlling at zero degree in this case..
    hmmm then maybe i guess a trip to the service center is in order...

  14. #14
    Member kwanhan's Avatar
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    Default Re: question on flash, underexposure

    Flash has been dropped off at the service center, thankfully within walking distance from my house.

    Will update thread again of the outcome once its back, if the problem is solved or if it still persists.

  15. #15

    Default Re: question on flash, underexposure

    Hi kwanhan, please update this thread when you get your flash back. I'm experiencing the same problem as yours on my Di622. I don't know if it's a factory defect or part of the design and since it was only a "Nissin" and not a "Nikon", I think the TTL mode in the Nissin can't really be as good as the Nikon's speedlights. If, however, your problem got solved after your visit to the service center, I will go back to the store where I bought mine too!

    Thanks,
    Ian
    Last edited by iankevinangeles; 20th January 2010 at 11:20 AM.

  16. #16
    Member kwanhan's Avatar
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    Default Re: question on flash, underexposure

    1 month later, back to update the thread LOL.

    The service center replaced my flash with a new unit instead.

    Underexposure and vignetting issues no longer present, working fine.

  17. #17
    Member dingaroo's Avatar
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    Default Re: question on flash, underexposure

    Good for ya! Maybe need to announce to all users of the brand of flash you are using to send it for servicing.
    A picture a day keeps the blues away!

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