Godox TT685-o TTL on Oly EM1Mkii

Discussion in 'Lighting Forum' started by PBBob, Nov 12, 2017 at 1:19 AM.

  1. PBBob

    PBBob New to Mu-43

    7
    Saturday
    The Villages FL
    As a flash novice, I have been trying figure out how do something that should be very simple. If done right, I figure in my nearly dark studio, I should get a pretty decent exposure. I do not: It is perhaps 2-3 ev dark.

    The setup I tried is a new Godox TT685-o mounted on my EM1Mkii camera on a tripod with the Oly 12-100 F4 lens at 100mm to a target on a white background 6 foot away. From the TT685-o instructions, it seems that all you do is select on the TT685-o: Mode = TTL. I also chose A(uto) for the zoom (it set itself too 100mm zoom) and HSS is Off. The instructions say nothing about setting up the EM1Mkii, so I assume any Mode (M,A,S,P) will work. I tried them all and they all consistently give very close to the same underexposed result.

    The attached picture shows more details on the settings.

    So what is the secret sauce to get TTL to work on the EM1Mkii?

    DSC01203.JPG
     
  2. Reflector

    Reflector Mu-43 Top Veteran

    734
    Aug 31, 2013
    That should make it work.. My Flashpoint Mini R2/TT350 is "plug and play" with my E-M5 and E-M1II, but I have heard that sometimes the Godoxs will TTL a little on the underexposed side, does manually dialing an offset and changing the scene make the illumination the same?
     
  3. Repp

    Repp Mu-43 All-Pro Subscribing Member

    Jan 27, 2011
    Oak Harbor, WA
    Just a simple thing... because this trips me up time to time... are you in E-shutter mode? And is your flash fully forward/seated in the hotshoe? Those 2 happen to me so often you'd think I'd check everytime... but I don't
     
  4. Reflector

    Reflector Mu-43 Top Veteran

    734
    Aug 31, 2013
    My Flashpoint Mini works in electronic shutter mode, you'll watch your shutter speed drop to sync with it.
     
  5. Repp

    Repp Mu-43 All-Pro Subscribing Member

    Jan 27, 2011
    Oak Harbor, WA
    For Pany's (GX7 and GX8), if you're using the electronic or silent shutter instead of the mechanical one, it simply won't fire the flash at all.
     
  6. PBBob

    PBBob New to Mu-43

    7
    Saturday
    The Villages FL
    The changes are readily observable when increasing FEC. E.g. with the EM1Mkii in Pgm mode, I took a shot of a CCPP target without flash with dim room light, got 1/2 sec, f4, ISO 200 and it looks very good. When I added 1.3 stops of FEC using the TT685-o in TTL, the EM1Mkii still in Pgm mode shoots 1/60 sec, f4, ISO 200 and the exposures were very similar.

    I was not expecting the offset (1.3 ev) to be nearly that high.
     
  7. PBBob

    PBBob New to Mu-43

    7
    Saturday
    The Villages FL
    I have no problems with the TT685-o flashing. I have the Silent Mode=Off, so using the mechanical shutter. Anti-Shock = 0, Noise Reduction = Auto.

    It appears that adding 1.3 stops of Flash Exposure Compensation offsets the bad decision either my camera or the TT685-o is making on the correct TTL exposure.

    Are there any other tests to verify this amount of FEC is necessary?
     
  8. Repp

    Repp Mu-43 All-Pro Subscribing Member

    Jan 27, 2011
    Oak Harbor, WA
    see If it’s happening at different Fstops and iso settings? Or maybe you’re exposure area (center weight vs spot)? I rarely use ttl, but the v860 and tt350 are both pretty spot on for me.
     
  9. Reflector

    Reflector Mu-43 Top Veteran

    734
    Aug 31, 2013
    From TT350 owner:
    wrotniak.net: Godox TT350o Flash Unit

    This might be the case with your TT685 as well.
     
    • Informative Informative x 1
  10. christofp

    christofp Mu-43 Regular

    177
    Jul 21, 2012
    Yes, as Reflector said, some FEC seems to be necessary, regardless of flash brand used.

    I had Oly and Metz, now I have Godox. They all needed around 0.7 FEC to give a good exposure. I think the flash system is a little bit conservative, maybe Olympus metering is assuming that there is always enough natural light to mix in? Don't know.

    Regarding your special setup with the CCTV test chart, a white surface will always need additional EC and FEC to be "white" in the final Image. Therefore a 0.7 EC or with flash, a 1.3 FEC seems to be explainable and quite normal ...

    Regarding the Godox in special, it seems that Godox system gives me a reliable confident exposure in off-camera TTL. Without Godox, the optical masters always tend to mess up the exposure TTL-test flash. In contrast with GODOX and wireless, there is no master flash and I can resort to the 0.7 FEC as mentioned above and everything is OK.

    Christof
     
    Last edited: Nov 12, 2017 at 7:13 AM
    • Agree Agree x 1
  11. esoxhntr

    esoxhntr Mu-43 Regular

    40
    Jun 6, 2017
    grand valley, on
    this would be my guess too. the exposure metering system sees your white background and tries to make it grey, it's not smart enough to know your background is supposed to be white. not unlike shooting a bright snowy scene where you have to dial in some + exposure compensation as well.
     
    • Like Like x 2
  12. PBBob

    PBBob New to Mu-43

    7
    Saturday
    The Villages FL
    Thanks everybody for the suggestions and background of a history of requiring FEC in similar situations.

    esoxhntr and christofp make an excellent point suggesting that the exposure could be confused by the white screen the 4"x6" CCPP print is mounted on and try to make it gray. The CCPP represents only about 50% of the image area and the rest is white. Perhaps contributing to the problem is that I took the shots using the EM1Mkii's Digital ESP metering mode to measure the TTL exposure, so the white border has more influence than it should in this case.

    I will do some exposures on a medium gray background and add some with Center Weighted Averaging metering that will give the CCPP have much more weight in the exposure. I hope to post the results by tomorrow night.
     
  13. PBBob

    PBBob New to Mu-43

    7
    Saturday
    The Villages FL
    Turned out I ran a LOT more pictures trying to run this thing down than I expected - about 200 pics and 30 hours more! Being an experimental physicist as well as a photo enthusiast may be my curse. I used 3 different lens (Oly 12-100 f4, Oly 60 f2.8 and Pany 35-100 F2.8) on the EM1.2 and Panasonic GX8. I shot the CCPP target on white and grey backgrounds with full-field (ESP) and center-weighted exposure balance.

    I think I will have some interesting conclusions about the TT685O flash unit with this equipment, but I must do some more analysis before I present them.

    Thanks for your patience. Please stay tuned, I have not given up on this!
     
  14. dukeneverwinter

    dukeneverwinter Mu-43 Regular

    25
    Aug 6, 2013
    La Mesa
    The Clyde
    I just bought the same flash a noticed it was not getting the result I was expecting. I am glad that somebody had the same experience and figured out a solution. I was tempted to send it back.
     
  15. Clint

    Clint Mu-43 All-Pro Subscribing Member

    Apr 22, 2013
    San Diego area, CA
    Clint
    Some suggestions if you are using TTL, USE either Aperture or shutter priority with a set ISO of 200.

    Use Spot Metering (the spot on your subject)
    Shoot just a plain white poster board, then +1EV, then +2EV, then +3EV (EV setting need to be set on the flash)
    Shoot just a plain black poster board, then -1EV, then -2EV, then -3EV
    You can get white/black poster board at Walmart, Office Depot, Staples, Target, etc. very inexpensively.

    You could repeat those shots using ESP/Matrix metering.

    Then either use smaller cards or move back so you have a white area about 1/4 of the view area with all black/or very dark surrounding it. Take one shot using spot metering, then center weighted, then ESP/Matrix

    Reverse this scenario so you have a small dark area surrounding by white/or bright.

    This short run test will demonstrate how your camera and flash sets exposures. This is a KISS principle test, intended to quickly get you acquainted with camera/flash TTL metering.
     
  16. PBBob

    PBBob New to Mu-43

    7
    Saturday
    The Villages FL
    Hang in there. Since someone actually is awake at this hour, I will tip my hand a little and show you a bit of what have found and what I still want to do.

    Basically, my study is on using the TT685O's TTL capability. After a lot of work, I am beginning to see why many photographers just use Manual mode and bypass all this TTL stuff.

    For TTL, the camera is the controller. After the TT685O issues a small "preflash", which is measured by the camera TTL, the camera tells the flash through the hot shoe interface how large the main flash must be for proper exposure. The TT685O uses this to emit the main flash of correct intensity a tiny fraction of a second later, in sync with the camera sensor being fully exposed, to capture the picture.

    The problem with using the TT685O with my EM1.2 is that the TT685O apparently does not properly interpret the feedback message from the camera, so emits too small a main flash, by about a factor of 2.

    The picture attached photo shows a series of 7 exposures, starting with "no flash" (#239) as the target to match and then 6 flash pictures with increasing amount of FEC (Flash Exposure Compensation), added by me manually adjusting the +- dial in TTL A(zoom) mode. FEC = 1 is twice as much light as FEC=0. FEC=2 is 4 times as much. FEC = 0 represents the amount of flash the TT685O thinks it needs to use. Actually it needs about twice that.

    The analysis will be to determine which of the flash pictures best match the natural light picture. It is complicated a bit by the different color temperatures of the 2 light sources (~3000K room vs 5600K flash), evident in spite of using Auto Color Balance in the EM1.2. My further approach is to color balance the pictures in LRoom, then measure the brigtness of a few of the bottom row of white to black squares in candidate photos to find the best match. I believe you can already estimate that picture #234 or #235 will be the best match to the far left "no flash" picture #239. So the TT685O needed 0.7 to 1.0 FEC (added light) to properly expose the target by flash alone in a dark room.

    I think I can use the EM1.2's Flash Intensity Control set to ~1.0 (see manual, pg 60) to force the TT685O to produce the correct amount of light, so it will not be necessary to use the flash's FEC. The GX8 has a similar setting.

    If boosting the FEC significantly proves to be true, GODOX should update the firmware to correctly interpret the EM1.2's TTL main flash power message.

    Initial analysis indicates this correction will be much less when using the TT685O with the GX8.

    TT685O, TTL,A, EM1.2, Pgm, 12-100, CtrWt.
     
  17. PBBob

    PBBob New to Mu-43

    7
    Saturday
    The Villages FL
    Thanks for joining in Clint.

    You have suggested an interesting variety of tests to run. Concentrating on the first section, what are you looking for, e.g. in the camera's playback of the 8 shots, sfter you take the 4 photos of the white and 4 of the black poster board? How do you use what you see to determine how much, if any FEC correction you need to crank in on the TT685O?