Is it my flash that's overexposing??

Discussion in 'Digital Discussion & Q&A' started by yinzerparty, Feb 26, 2010.

  1. yinzerparty

    yinzerparty TPF Noob!

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    Hi,
    I have a canon rebel xs and bought the canon 430exII speedlite in November. It's been working great. I take nightlife photography, and it's been awesome. Faces are a good tone and come out perfectly lit.

    In the past few weeks I've had a huuuge problem with my flash. The batteries are fine-I've tried with putting new ones in. The first few pictures will turn out ok, then suddenly the pictures will be incredibly overexposed. Almost a total white out.
    So I take the flash off and put it back on, and everything's fine. This happens at least 2-3 times a night. I'm not changing any settings. The flash is pushed the whole way into the shoe also.

    Can someone please help me?? Is it settings that are getting screwed up? Has this happened to anyone else?
     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Welcome to the forum.

    Can you show up some examples? Hopefully along with the EXIF data.

    The camera & flash use something called E-TTL metering to determine the exposure from the flash. It uses a pre-flash, reads the resulting light and then fires again for the exposure. The flash exposure will vary, depending on what is in front of the lens, so if the scene is basically the same and the flash output changes, then you may have a problem....but it's hard to say until we can see some images.

    Also, are you taking shots in rapid succession?
     
  3. Garbz

    Garbz No longer a newbie, moving up!

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    Typically if the problem is intermittent then there may be some intermittent contacts. Grab a dark pencil (2B or softer) and scribble on all the hotshoe contacts on the flash and on the camera. Graphite is a great conductor.

    See if that fixes it.
     
  4. yinzerparty

    yinzerparty TPF Noob!

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    garbz,
    would this be a one time thing? like i should rub it and it should be good from then on out?


    here are some examples:
    (settings on both are iso 200 f/5.6 1/5sec.)
    [​IMG]

    to

    [​IMG]


    another example:
    (settings iso 200 f/5.6 1/20sec on first, all but 1/15sec. on second
    [​IMG]

    to

    [​IMG]


    i've thought maybe the flash is hot, but it doesn't happen when i'm only rapidly shooting just one area. If I've been shooting for awhile and move around to different parts of the room, my settings stay the same, but still some pictures will be very overexposed and blownout until i remove the flash and put it back on.
    (Setting iso 800 f/5.6 1/40sec)
    [​IMG]
     
  5. Derrel

    Derrel Mr. Rain Cloud

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    I pulled your samples into PS, and it said "no strobe return detection (o)", but it also said "Compulsory flash firing (1)", on both the well-exposed and the grossly overexposed photos. I'm not sure how well that squares with your camera, but it would seem to me that there *SHOULD* be a strobe return detected if the camera is recognizing that it has a flash firing in the hot shoe, right?

    What flash mode are you using? Is it possible that the camera is set to spot or semi-spot light metering? Is the flash perhaps set to a manual power mode, so that the camera does not actually monitor the amount of flash that returns from the scene?

    Just sort of thinking out loud here. One thing I think could be happening is that the hotshoe or the foot of the flash has worn a bit, or a contact is dirty, or there is only intermittent perfect contact, and so when the contact is not 100%, the system does not work correctly. DOes it work LESS-reliably when shooting talls??? WHich might indicate that the weight of the flash is "pulling" the flash foot away from the hotshoe's contact points, due to the leverage the flash exerts when the camera is in tall mode.

    I have actually heard of the above problem on another forum, from a wedding shooter who used a flash in the hotshoe a large amount of the time.
     
  6. Garbz

    Garbz No longer a newbie, moving up!

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    Cleaning contacts is not a one time thing. It gets done when it's needed. Your local electrical hobby store should have a far better solution to cleaning contacts than rubbing it with a pencil, but there's no denying that a pencil will do wonders when there's no RadioShack around.
     
  7. iskoos

    iskoos TPF Noob!

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    I have pretty much the same equipment. I never experienced this problem yet and mostly because I don't use flash alot. But I will be following this thread to see what actually is going on in your case.

    I haven't looked at your exif data but you are in ETTL mode right? And by any chance would you be recomposing after focusing on your subject? I heard that this is not a good idea in ETTL mode unless you lock the flash exposure...
     
  8. IgsEMT

    IgsEMT No longer a newbie, moving up!

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    Seems like meter mode is the issue
     
  9. Garbz

    Garbz No longer a newbie, moving up!

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    Given that the ExIF data for each pair of images is identical save for the time taken, and that each pair of images (especially the top) have a similar distribution of contrast around the frame, and similar focal point; how did you come to that conclusion?
     
  10. Fusion

    Fusion TPF Noob!

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    This seem the best initial idea as it does sound to be a connection problem, try it nothing lost... :thumbup:
     

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