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Godox v860ii-O Reduces Flash Power by Half in Manual Mode with Change in Shutter Speed

I just purchased a Godox v860ii-O for my Olympus OM-D E-M1 mkII.  I set the camera to manual mode at f/4 and 1/250 sec (sync speed) and a base ISO of 200.  I set the flash (on-camera) to manual mode (1:1 power) and manual zoom (100 mm max).  What I noticed is that the distance reading on the flash with these settings is 30 feet.  However, when I change the shutter speed to 1/160 sec, the distance reading on the flash increases to 60 feet.  From 1/160 sec and lower, the distance reads 60 feet.  Once I increase the shutter speed to 1/200 sec or 1/250 sec, the distance drops by half to 30 feet.

Given that I have kept the flash power constant (manual 1:1), the ISO constant (200 - auto ISO off), the aperture constant (f/4), I would have thought that the distance reading would not change with shutter speed.  I have double checked to make sure that my camera's sync speed is 1/250 sec.  Given that flash output in manual mode should not be affected by shutter speed and only by power, aperture, ISO, and distance (PAID), does anyone have an idea of why my flash output drops in half at 1/200 sec and 1/250 sec?  This effectively reduces my sync speed to 1/160 sec for maximum flash output.

I haven't found this issue on any of the Godox or Olympus sites or in reviews.  I upgraded the Godox firmware to the latest (1.4) and still get the same problem.

Thanks!
Miles
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Comments

  • Neil vNNeil vN Administrator
    You are going into High-Speed Flash Sync ... this will cut your flash power by half (or more.)

    Go over this tutorial - it will explain more:

  • Hi, Neil.  Thank you for your response.  I have reviewed your tutorial, but I am still confused.  I am using my flash directly on-camera, so there should be neglible propagation delay.  Also, my camera sync speed is 1/250 sec, but I am seeing the distance reduced in half at 1/200 sec.  I do not have my flash in HSS, but it sure seems like it is given the 2-stop reduction.
  • Neil vNNeil vN Administrator
    The max flash sync speed of the Olympus OM-D E-M1 mkII, is 1/250th. 

    So there shouldn't be such a drop.  However, with the Nikon D4 and SB-910, you could see a similar drop as it approached max flash sync speed -- it wasn't linear right up to the max flash sync speed. 

    Something in the software of the Nikon D4 and SB-910 caused that.  With the Nikon D5 and the SB-5000, it is behaving correctly again ... there is a linear relationship. 

    That's all I can really decipher here ... I am going to assume it is the way the camera is programmed.  (Unless someone has some real concrete advice and info here.)
  • Neil vNNeil vN Administrator
    Oh, and the original Canon 5D did something similar. When you were at 1/200 (the max), and you were working in the normal flash sync mode, you would get a specific distance. But just switching HSS on (without affecting any other setting), it would drop the distance the flash would reach.  So even AT max sync speed, the range would drop, depending on whether you had HSS enabled or not. 
  • Thank you very much!  I will just need to adjust to the effective lower sync speed.

    I really learned a lot from your on-camera flash book and Craftsy video.  Thank you for sharing your knowledge and experience in such a clear way.
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