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Thread: Flash, at the back end of an exposure

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    Benboxer's Avatar
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    Flash, at the back end of an exposure

    I am wondering if DSLR will let you use the flash at the end of an exposure, as opposed to the beginning. Joe McNally refers to this as "rear curtain". It allows the foreground subject to be sharply delineated without any ghosting .Ghosting occurs when the flash is used at the beginning of the exposure, allowing the background to overlap and obscure the foreground subject during long exposures.

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    Re: Flash, at the back end of an exposure

    Yes you just set the camera for rear curtain synch and depending on your camera and flash a suitable speed. Mine is max 1/125 but Canon with more than two digit prefix such as 350D, 500D are 1/90.

    Professional ones with 1 digit prefix such as the 5D are much faster.

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    Benboxer's Avatar
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    Re: Flash, at the back end of an exposure

    Thanks! It's good to know that that is a common feature and that I will have a choice when i upgrade to an DSLR!

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    Re: Flash, at the back end of an exposure

    Yes, to second that, you can use second (rear) curtain sync for flash on a DSLR (at least on Canon ones, but I'm sure that the others would do it as well). It's very useful if you're mixing ambient light and flash and you can't get a short enough exposure to guarantee to freeze all of the motion. In this case firing the flash at the end of the exposure often leads to a more reasonable looking result.

    Will

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    Re: Flash, at the back end of an exposure

    Quote Originally Posted by Benboxer View Post
    It allows the foreground subject to be sharply delineated without any ghosting .Ghosting occurs when the flash is used at the beginning of the exposure, allowing the background to overlap and obscure the foreground subject during long exposures.
    Not quite.

    You get the ghosting anyway, it's just that it occurs behind the direction of travel (which looks better), not infront of it.

    (And yes, I've got Joe's book) (Hot Shoe Diaries).

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    Benboxer's Avatar
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    Re: Flash, at the back end of an exposure

    Yes, that's the book, Learning how to use a flash and/or flashes was informative, as I normally don't use a flash (I have a pop-up with no hot shoe)and have problems getting a good composition with content AND lighting. I don't mind the ghost trail, but would like to see the subject exposed properly with good delineation!

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    Re: Flash, at the back end of an exposure

    Quote Originally Posted by Benboxer View Post
    Yes, that's the book, Learning how to use a flash and/or flashes was informative, as I normally don't use a flash (I have a pop-up with no hot shoe)and have problems getting a good composition with content AND lighting. I don't mind the ghost trail, but would like to see the subject exposed properly with good delineation!
    Keep in mind that the ghosting is invariably caused by ambient light; if you have a shutterspeed that's high enough (say 1/200th @ ISO 100 @ F4 or above) then very little ambient light will get in and the flash will freeze all motion. The "downside" though is that the flash has to then assume responsibility of illuminating the whole scene (including background)

    Note: to get a high shutterspeed you'll need to use either shutter priority or manual modes.

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    arith's Avatar
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    Re: Flash, at the back end of an exposure

    I would like to correct a mistake I made earlier; it is indeed correct that Rear Curtain Sync can be set on dslr in the Canon range anyway.

    But the speeds I gave were for X-Sync and not even these are right. Doing some tests I was confused why 1st curtain sync was shown set in exif and was thrown by reading a speed of 1/125 for intermediate dslr in a webpage where my 10D is 1/200 for X-Sync and so assumed it must refer to the rear curtain.

    My tests show rear curtain sync cannot be set for speeds greater or equal to 1/30 on my body either with external flash or internal flash. Sorry, Ill keep quiet from now on.

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