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Thread: Help needed on auto Thyristor flash

  1. #1

    Default Help needed on auto Thyristor flash

    I'm learning how to use an external auto-thyristor flash (a emoblitz 328 to be exact) on a d70. I have difficulties in understanding the following situations:

    1) When shooting in dark situations using A mode (to match flash setting of f/2.8), camera sets a very low shutter speed, as though no flash is present. Pic is overexposed.

    2) When trying to bounce flash, pic is underexposed. (i thought the sensor is supposed to detect how much light enters, not how far subject is from cam?)

    I thought of using M mode to fix aperture and prevent cam from setting low shutter speeds. But i dunno what speed to set to have a good balance between subject and background. Is there any guide i can follow?

    By the way, is the sensor directional? Will the flash output be affected if the subject is off centered?

    Thx

  2. #2
    Moderator catchlights's Avatar
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    Default Re: Help needed on auto Thyristor flash

    Quote Originally Posted by ahsosl1e8 View Post
    1) When shooting in dark situations using A mode (to match flash setting of f/2.8), camera sets a very low shutter speed, as though no flash is present. Pic is overexposed.
    the flash is not a dedicated flash, and D70 does not know a flash is been use, so when using A mode in low light situration, it will go slow shutter speed.
    Quote Originally Posted by ahsosl1e8 View Post
    2) When trying to bounce flash, pic is underexposed. (i thought the sensor is supposed to detect how much light enters, not how far subject is from cam?)
    wrong, most likely is out of range.
    Quote Originally Posted by ahsosl1e8 View Post
    I thought of using M mode to fix aperture and prevent cam from setting low shutter speeds. But i dunno what speed to set to have a good balance between subject and background. Is there any guide i can follow?
    use your camera meter, normally background under 1~1 stops is good.
    Quote Originally Posted by ahsosl1e8 View Post
    By the way, is the sensor directional? Will the flash output be affected if the subject is off centered?
    it should be about standard lens coverage, your flash manual does state.
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  3. #3

    Default Re: Help needed on auto Thyristor flash

    wrong, most likely is out of range.
    Hmm... i was doubtful coz the flash din seem to go full power (recharges almost immediately). Anyway, does it mean that given the right conditions, auto flashes should automatically compensate for any method of indirect flash?

    it should be about standard lens coverage, your flash manual does state.
    What i wanted to know is that for eg: i have a subject in front of a white wall. If i point straight at the subject, will i get a different flash exposure compared to if the subject is to the side of the pic (ie off center)?

    use your camera meter, normally background under 1~1 stops is good.
    In this case, would you suggest i use Av mode and set EV -1 ~ -1.7?

    Thx

  4. #4
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    Default Re: Help needed on auto Thyristor flash

    Chances are that you might have bounced the light either too much in front or behind the subject. Was there anything in the picture that was properly exposed? Also, if there is something in the frame that is highly reflective, it can confuse the thyristor into underexposing the picture (look for bright spot in the picture for this instance)

  5. #5

    Default Re: Help needed on auto Thyristor flash

    For bouncing the flash, try to use a bounce card if u have it helps to distribute abit of the flash towards the front.

    Since u are using a DSLR, just use the following as a guide for indoor shoots (My own experience shooting in a ballroom), ISO 400 F4-5.6 1/30-1/60s in manual mode, Should be a starting point, and u can check ur histogram to see if u need more power.

    So to give more power to the flash set it to the next smaller aperture setting and see the effects, I use to have a Vivitar 285.

    Check distances, when using 'pure bouncing' (no bounce card) there might not be enough flash return to give a good reading to the flash, there should be a led or something to tell u the flash suspects the picture might be underexpose.

  6. #6

    Default Re: Help needed on auto Thyristor flash

    a quick tip for you to get more flash using the "auto" mode.
    use cell-tape, stick a piece of tissue over the sensor (cover it).
    now you'll trick the sensor and get more light in auto-mode

  7. #7
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    Default Re: Help needed on auto Thyristor flash

    I believe he did mention that the flash recycled almost immediately, indicating that no underexposure was noted.

  8. #8

    Default Re: Help needed on auto Thyristor flash

    Quote Originally Posted by MDZ2 View Post
    I believe he did mention that the flash recycled almost immediately, indicating that no underexposure was noted.
    if the flash recycled immediately, it means that full power wasn't used.
    is that the reason for under-exposure?

  9. #9
    Moderator catchlights's Avatar
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    Default Re: Help needed on auto Thyristor flash

    Quote Originally Posted by ahsosl1e8 View Post
    Hmm... i was doubtful coz the flash din seem to go full power (recharges almost immediately). Anyway, does it mean that given the right conditions, auto flashes should automatically compensate for any method of indirect flash?
    Please state what bounce methods you use? ceiling bounce? bounce card? omnibounce?
    the only explanation for underexposed are:
    #1, your bounce device have spill light into your flash sensor.
    #2, you place your subject very small and in front of a white wall.

    Quote Originally Posted by ahsosl1e8 View Post
    What i wanted to know is that for eg: i have a subject in front of a white wall. If i point straight at the subject, will i get a different flash exposure compared to if the subject is to the side of the pic (ie off center)?
    your flash is not a ttl dedicated flash, the flash sensor only take reading on the centre portion area.


    Quote Originally Posted by ahsosl1e8 View Post
    In this case, would you suggest i use Av mode and set EV -1 ~ -1.7?

    Thx
    you have to use manual exposure mode on camera, else if it is outdoor the shutter speed will go beyond sync speed, and indoor the shutter will go below hand held speed.
    btw, I'm not sure how to set Av mode on D70, cause I can't find the Av mode dial on D70.
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