550ex flash light emission pattern

Discussion in 'Digital Photography' started by PeterH, Sep 19, 2004.

  1. PeterH

    PeterH Guest

    I couldn't find another suitable NG to post this query and found no info on
    the net.

    Is it possible to find a flash emission (exposure?) pattern for a 550EX
    flash or any other flash unit for that matter?

    I want to see how the flash throws light out.

    Is it evenly spread? Are there any "blind" spots where the light is less
    intense than other areas eg in the corners of the head?

    Why a rectangular shape to the flash head instead of say circular?

    How effective are the circular patterns, on the head, in evenly emitting
    light?

    regards

    PeterH
     
    PeterH, Sep 19, 2004
    #1
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  2. PeterH

    Jim Guest

    "PeterH" <reply to > wrote in message
    news:6c43d.35342$...
    > I couldn't find another suitable NG to post this query and found no info

    on
    > the net.
    >
    > Is it possible to find a flash emission (exposure?) pattern for a 550EX
    > flash or any other flash unit for that matter?

    Certainly. Just take of picture of a dark wall with the flash engaged..
    >
    > I want to see how the flash throws light out.
    >
    > Is it evenly spread? Are there any "blind" spots where the light is less
    > intense than other areas eg in the corners of the head?

    More likely that there will be a hot spot at the center, but you need to
    test your flash.
    >
    > Why a rectangular shape to the flash head instead of say circular?

    Because the sensor is rectangular.
    >
    > How effective are the circular patterns, on the head, in evenly emitting
    > light?

    Why not test your own flash to determine how well it works?
    Jim
     
    Jim, Sep 19, 2004
    #2
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  3. PeterH

    Bill Hilton Guest

    >From: "PeterH" replyto

    >Is it possible to find a flash emission (exposure?) pattern for a 550EX
    >flash or any other flash unit for that matter?
    >
    >I want to see how the flash throws light out.
    >
    >Is it evenly spread? Are there any "blind" spots where the light is less
    >intense than other areas eg in the corners of the head?


    Easiest way to check is to set it for say 80 or 105 mm and shoot manually with
    the ambient exposure underexposed by 2-3 stops. Use a wider lens, flashing on
    a white or grey wall. You'll be able to see the flash pattern clearly and if
    shooting digitally you can measure the center and surrounding areas to see if
    there's much fall-off. Then shoot again at the correct focal length at say f/8
    and see if you see any fall off at the corners vs the center, realizing that
    the lens may be the cause of some of the drop off too.

    >Why a rectangular shape to the flash head instead of say circular?


    Probably because the image format is 3:2.

    >How effective are the circular patterns, on the head, in evenly emitting
    >light?


    Test it and see, should work fine though.

    Bill
     
    Bill Hilton, Sep 19, 2004
    #3
  4. PeterH

    Alan Browne Guest

    PeterH wrote:
    > I couldn't find another suitable NG to post this query and found no info on
    > the net.
    >
    > Is it possible to find a flash emission (exposure?) pattern for a 550EX
    > flash or any other flash unit for that matter?
    >
    > I want to see how the flash throws light out.
    >
    > Is it evenly spread? Are there any "blind" spots where the light is less
    > intense than other areas eg in the corners of the head?
    >
    > Why a rectangular shape to the flash head instead of say circular?
    >
    > How effective are the circular patterns, on the head, in evenly emitting
    > light?


    Underexpose a shot by 2 or 3 stops on a white wall. Set the
    flash head zoom to about 50mm and shoot at 200mm. The resulting
    image will tell you (set camera to flash comp -1 or -2 should do
    it ... it will already underexpose a white wall).

    In photoshop use the "info" box to 'probe' the image. Use the
    center as reference (should give R=G=B, that's your ref. Then
    explore everywhere else).

    The head is rectangular because the film is 3:2 aspect ratio.

    The little circles help. Usually cut as a fresnel lens. They
    scatter the light with lots of overap.

    Have fun.


    --
    -- rec.photo.equipment.35mm user resource:
    -- http://www.aliasimages.com/rpe35mmur.htm
    -- e-meil: there's no such thing as a FreeLunch.--
     
    Alan Browne, Sep 20, 2004
    #4
  5. PeterH

    Bill Hilton Guest

    >From: Alan Browne

    >Set the flash head zoom to about 50mm and shoot at 200mm.


    I would do it the other way, shoot wider than the flash is set for so you can
    see the entire flash pattern. Doing what you suggest will only let him see a
    small % of the area covered by the flash.
     
    Bill Hilton, Sep 20, 2004
    #5
  6. PeterH

    Alan Browne Guest

    Bill Hilton wrote:
    >>From: Alan Browne

    >
    >
    >>Set the flash head zoom to about 50mm and shoot at 200mm.

    >
    >
    > I would do it the other way, shoot wider than the flash is set for so you can
    > see the entire flash pattern. Doing what you suggest will only let him see a
    > small % of the area covered by the flash.


    a) Just testing to see if you were paying attention!

    b) OOOPPPS. Yes fo course. My head was on backwards.

    Your choice, a/b.

    Cheers,
    Alan


    --
    -- rec.photo.equipment.35mm user resource:
    -- http://www.aliasimages.com/rpe35mmur.htm
    -- e-meil: there's no such thing as a FreeLunch.--
     
    Alan Browne, Sep 21, 2004
    #6
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