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Thread: Confusion on 1.6x field of view crop with external flash unit

  1. #1
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    Red face Confusion on 1.6x field of view crop with external flash unit

    Hi all,

    Hope somebody can help me with this.
    I just brought a 400D & 430ex external flash unit.

    I know 400D is a 1.6x field of view crop sensor, that mean all your lenses attach on the camera body have to x1.6 on the metering.

    I had a 17-85mm lens and will be treated as 28-136mm.

    The question is on the flash metering. i notice with i turn the zooming on the lens, the flash metering will automatically change the flash meter according to the lens, but is it the metering figure still acurate under 1.6x sensor?

    which I get confuse here. for example: my lens zoom at 80mm and x1.6 = 128mm, but your flash meter is showing 80mm.

  2. #2
    Member BigRooster's Avatar
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    May 2007
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    Default Re: Confusion on 1.6x field of view crop with external flash unit

    Quote Originally Posted by louisgce View Post
    Hi all,

    Hope somebody can help me with this.
    I just brought a 400D & 430ex external flash unit.

    I know 400D is a 1.6x field of view crop sensor, that mean all your lenses attach on the camera body have to x1.6 on the metering.

    I had a 17-85mm lens and will be treated as 28-136mm.

    The question is on the flash metering. i notice with i turn the zooming on the lens, the flash metering will automatically change the flash meter according to the lens, but is it the metering figure still acurate under 1.6x sensor?

    which I get confuse here. for example: my lens zoom at 80mm and x1.6 = 128mm, but your flash meter is showing 80mm.

    Your flash metering is correct at 80mm.

    The distance of your subject from you does not change, whether it is 1.6x or full-frame. It is just that at 1.6x, your field of view is narrower (think in terms of a big box for FF, and your 1.6x FOV is a smaller box in the bigger box). So, it gives the equivalent FOV as if it is for 128mm.

  3. #3

    Default Re: Confusion on 1.6x field of view crop with external flash unit

    The in-built zoom is only there so that your flash doesn't needlessly light up areas outside the FOV of the lens. Metering technique stays the same whichever focal length you're at.

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