Controlling Flash Output Through Sync Cable?

Discussion in 'Lighting Forum' started by perpetualjon, May 16, 2015.

  1. I am delving into the world of strobe photography and have been having a difficult time controlling the light output of a 600W off-camera strobe using the sync cable. It doesn't seem like the output power dial makes any difference in the exposure. Here's what I'm using:

    GH3 with a Mettle 600AD strobe -using the sync cable to control the shots for now. Will get a wireless trigger if the need arises but with mostly studio shots to do, I'm not expecting to that soon.

    It looks like it shoots full-power no matter what I adjust. I have to stop down the aperture well into the f20 range to control the exposure and that affects the sharpness of the image due to diffusion. I can't increase the shutter speed faster than 1/250 or I get black bars over the image.

    The menu options don't look like they help either -meaning I can't seem to adjust anything regarding power or timing in the camera that makes any difference to the strobe through the cable. Would a wireless trigger help here? My fear is that I either have a broken strobe that just ignores the power output dial, or there's no way to control the output through a sync cable...

    Can anyone help here?
  2. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    There's no way to control a flash via sync cable. It's two wires, when they're shorted the flash fires.

    The head should have a dial of some sort to turn it down, sometimes they have a switch to change range between a high and low on the dial (high might be 1/1 to 1/4, low might be 1/4 to 1/64 or something like that). I don't know the model you're using however.
  3. mettle-600ad.
    Yeah, I think my strobe may be broken. I've done test shots with it at a full 1/1 and all the way down to 1/32 (I even recently learned about the need to discharge the capacitors when lowering the power before the next photo). What I got was the exact same exposure on an all-manual mode with the PC sync cable.
  4. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    Does the modeling light change output when you move the dial? It should have two modes (and off) on the top left switch, full power and one slaved to the power output.
  5. The modeling light does change with the power output when moved to the upper position. However, the total flash output is still the same in either setting.
  6. BillW

    BillW Mu-43 Regular

    Oct 22, 2012
    Scranton, PA
    Forgive me if this seems basic, but not knowing your setup, I'll try to cover all factors:

    You want to be in Manual mode. I'd start with 1/125 @ f11.

    Don't use Auto ISO...instead start with 200 ISO.

    Once you remove the exposure variables on the camera side, you can get a better idea of what the flash is doing.

    Depending upon your flash to subject distance, you may have too much power if you are shooting with direct light. Try diffusing with an umbrella, softbox, or bounce it off a wall.

    A flash meter will help quite a bit, if you can get your hands on one, and give you instant feedback on your flash power

    Start with Flash white balance, and learn to do a custom WB if you don't already.
  7. My setup: GH3 with a single 600W strobe in a 47" softbox. I'm using the Olympus 12mm/f2.0 lens for my test shots at the moment. I don't have a light meter yet so I've been doing test shots at a variety of settings and checking the histogram of the exposure to verify the right settings. I started with a very high aperture (f22) and worked my way down with the shutter at the fastest it would go without problems (1/250) keeping the ISO at 100. I quickly found that my exposures were proper but the image quality was terrible -fairly fuzzy and a lack of sharpness. Reading into it, I learned that high apertures can result in light diffraction that affects sharpness (especially at f-stops as high as f22). However, since I can't really set my shutter speed any faster, I'm still stuck in the high ranges of f11 to f16 to compensate for the flood of light from such a powerful flash. The type of shots I want to do demand this but I can't seem to make it work with the equipment I'm now using.

    I've been reading about high speed strobe work with other systems that they mention using a "FP" remote to control the strobes. Supposedly they trigger the flash when the first curtain of the shutter opens and not after -and I believe this is when the PC sync cable fires which may explain my problem. I'm probably going to start looking around for a reasonably priced wireless trigger system that can help me get past this issue...

    Here is a discussion about the same issue on another site. The first photo shown is exactly what I'm aiming for: extremely high shutter speed, a moderately high f-stop, and large amount of light will render a super sharp yet very dark exposure:
  8. BillW

    BillW Mu-43 Regular

    Oct 22, 2012
    Scranton, PA
    You could have a bad flash unit, or it may just be too bright without any type of diffusion.

    Test it this way w/o a camera: Lowest setting, pointed at a wall, squint your eyes and pop the flash off. Keep increasing the power (1/32, 1/16, 1/8, etc.), and see if you notice a difference in both flash intensity and duration if it's working properly, as well as a difference in recycle time as you increase power.
  9. Ross the fiddler

    Ross the fiddler Mu-43 Hall of Famer

    FP TTL is only for dedicated flashes (FL600, FL50R etc) connected to the hotshoe or by RC mode (with commander flash). Using the sync cable to your flash you can only do it all in Manual & F8 is a good standard starting point, but changing your shutter speed is not going to make any difference. Just leave it between 1/60 sec to 1/250 sec if the flash works in that range. The rest of it is the distance the flash is to the subject, diffuser & camera aperture. Also, does that flash have a variable beam (angle)? If you have no diffuser then you may have to move it back a lot further & then the power level adjustment on the flash should be noticeable if it is working OK.
  10. Yeah, I think I have a bad flash unit. I just did some test shots working the range from lowest to highest and the intensity and recycle times were identical...