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Thread: correct metering with a flash

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    correct metering with a flash

    Hi - I have just bought an external flash (SB600) for my Nikkon D90.

    One thing I do not undersrand is how to correctly meter for a shot while using the flash.

    The camera usually tells me the correct shutter speed to shoot in a particular apperture but that's with the existing lighting conditions. If I use the flash, the fact that there will be extra light available from the fladh is not known to the camera. the result is severe overexposure if I use the camera suggested reading AND the flash. I normally shoot in Manual mode and have to bypass the camera shutterspeed suggestion and shoot multiple stops under while using the flash and then work my way up until the correct exposure is recorded which is kind of hit and trial.

    The other issue is often the exposure is either too dark or too bright and for portraits the subject (read family members) get frustrated to wait for multiple shots for the correct exposure.


    Is there a better way to use the flash and metering? Please help....

    Cheers
    DJ

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    In Training MarkChap's Avatar
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    Quote Originally Posted by dbose View Post
    Hi - I have just bought an external flash (SB600) for my Nikkon D90.

    One thing I do not undersrand is how to correctly meter for a shot while using the flash.

    The camera usually tells me the correct shutter speed to shoot in a particular apperture but that's with the existing lighting conditions. If I use the flash, the fact that there will be extra light available from the fladh is not known to the camera. the result is severe overexposure if I use the camera suggested reading AND the flash. I normally shoot in Manual mode and have to bypass the camera shutterspeed suggestion and shoot multiple stops under while using the flash and then work my way up until the correct exposure is recorded which is kind of hit and trial.

    The other issue is often the exposure is either too dark or too bright and for portraits the subject (read family members) get frustrated to wait for multiple shots for the correct exposure.


    Is there a better way to use the flash and metering? Please help....

    Cheers
    DJ
    OK to start with the camera DOES know the flash is there and it actually calculates how much extra light the flash will deliver.

    Not 100% sure with Nikon, but with Canon, when shooting manual the camera tells the flash to produce enough light to be the primary light source for your selected exposure (Shutter Speed, Aperture and ISO), hence the tendency to over expose.

    When shooting in either Shutter Priority or Aperture Priority the camera then expects the flash to used for FILL and will drop the output accordingly to only fill the scene as exposed by the meter.

    I use Flash Exposure Compensation to drop the output by an amount of my choosing, when shooting birds I will always start with -2/3 FEC, if I am inside or shooting people I will normally start at -1 1/3 FEC.

    If you want just fill light use Shutter or Aperture Priority

    As I said this is based on what I know about Canon
    Smoke Alarms Save Lives, Install One Today
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    Cheers, Mark


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    Way Down Yonder in the Paw Paw Patch jim's Avatar
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    Just some basic info here, since I'm not technical, but the camera will try to balance flash and ambient light, but it's easy to overwhelm it in Aperture priority because you generally can't set a shutter speed faster than 1/320, or sometimes even less. Viewfinder should read HI.

    In shutter priority the camera can balance flash and ambient much more effectively, because it's free to set any aperture.

    Or something like that.

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    Quote Originally Posted by MarkChap View Post
    OK to start with the camera DOES know the flash is there and it actually calculates how much extra light the flash will deliver.

    Not 100% sure with Nikon, but with Canon, when shooting manual the camera tells the flash to produce enough light to be the primary light source for your selected exposure (Shutter Speed, Aperture and ISO), hence the tendency to over expose.

    When shooting in either Shutter Priority or Aperture Priority the camera then expects the flash to used for FILL and will drop the output accordingly to only fill the scene as exposed by the meter.

    I use Flash Exposure Compensation to drop the output by an amount of my choosing, when shooting birds I will always start with -2/3 FEC, if I am inside or shooting people I will normally start at -1 1/3 FEC.

    If you want just fill light use Shutter or Aperture Priority

    As I said this is based on what I know about Canon
    Thanks - so if I shoot in aperture priority or shutter priority then I can use the camera suggested metering. If I shoot in manual, I either meter below the suggested shutter speed or use flash exposure compensatiion. Is that what you meant?

    Nikkon works similar to Cannon in this case.

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    Member DesmondD's Avatar
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    Quote Originally Posted by dbose View Post
    Thanks - so if I shoot in aperture priority or shutter priority then I can use the camera suggested metering. If I shoot in manual, I either meter below the suggested shutter speed or use flash exposure compensatiion. Is that what you meant?

    Nikkon works similar to Cannon in this case.
    I shoot Nikon and did a blog with some beginners flash info .
    TTL flash does not try to balance with the ambient but TTL/BL does .
    Have a look at that info and see if it helps !


    .

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    Quote Originally Posted by dbose View Post
    If I shoot in manual, I either meter below the suggested shutter speed or use flash exposure compensatiion. Is that what you meant?

    Nikkon works similar to Cannon in this case.
    Further to Jim's advice, the general principle is that shutter speed affects the ambient light and aperture affect the amount of light you get from the flash - you can use it to balance ambient and flash, but really what you are doing is increasing or decreasing the amount of ambient, and not affecting the flash.

    Simple reasoning is that the flash only lasts 1/10,000th of a second (or some large number), so if your shutter speed is 1/200th or 1/50th or 1/500th, then you will see no change in the amount of light from the flash in your shot. What will happen is that the varying shutter speeds will vary the amount of ambient light in the shot.

    If you want to vary the intensity of the flash and maintain a particular shutter speed you will need to use flash compensation or change the power of the flash, or alter the aperture. If you also have a particular aperture in mind for DOF reasons, you are left with only altering flash output.

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    Member Jeremy's Avatar
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    All one needs/wants to know, in 3 parts, is here - biased towards Canon EOS but applies generally:

    http://photonotes.org/articles/eos-flash/

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    Member glenwood's Avatar
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    This is very good site if you are intrested in on camera flash.

    http://neilvn.com/tangents/

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