No clue about what I'm doing...

lynnmalynnma Moddess EmeritusHomosassa, Florida (Paradise)Registered Users, Retired Mod Posts: 5,163

Hi ziggy and all.. long time no visit, hope you guys and gals are all well.

I dug out my practically unused Canon 600EX-RT Speedlite and my Canon Speedlite ST-E2 transmitter and proceeded to relearn how to switch them all on... I have the Speedlite set on the same channel as the transmitter and it's on Slave.. I then added some el cheapo Slave AC Flashes and whilst they all flash when I press zee button.. the speedlite's power is greatly reduced.. when I use the speedlite alone it's perfect.. I'm assuming that it's reacting to the extra light in the room and reducing it's power to try to match it.. or something? I don't have a second speedlite and would like to use these (unused) slaves but obviously I'm doing something wrong or they are not compatable in some way. Very rookie question I know but I always shoot in natural light and really must move onto more flash... specially as I have this lovely Speedlite sitting there doing nothing. Can you shed any light. I can't see any way to group the AC flashes and group the speedlite.. I'm sort of glazing over...
Great new website by the way


  • ziggy53ziggy53 Still learnin'still lovin Super Moderators Posts: 21,555 moderator
    edited April 29, 2017

    The first thing to understand is that the Canon 600EX-RT Speedlite and Canon Speedlite ST-E2 "Master/Controller" are working via Canon E-TTL optical communications.

    The ST-E2 actually sends several bursts of light, although it all happens so quickly humans don't generally perceive more than a single flash pulse. The first pulse of light is to test and calibrate the reflectivity of the subject matter defined at the distance the camera's AF section determined. Based on the return light from the subject, the camera adjusts the flash exposure component of the total exposure. (The other part of the exposure was previously determined by the ambient light detected by the metering module in the camera.)

    The "el cheapo Slave AC Flashes" probably have a simple optical trigger which responds (flashes) to the first pulse of light from the ST-E2, which makes the returned light from the subject brighter than normal. This apparent "brightness" makes the ST-E2 send a signal to the 600EX-RT Speedlite to turn down its output. The ST-E2 now sends a pulse to trigger the 600EX-RT Speedlite for the "taking" pulse, which the Speedlite adjusted down because the Slave AC Flashes essentially messed up the E-TTL system.

    If you mount the 600EX-RT Speedlite directly atop the camera, and put the 600EX-RT Speedlite in manual mode, the Speedlite will only emit one pulse of light, and the Slave AC Flashes will respond by contributing to the exposure. Vary the output of the Speedlite depending on whether the intent is for the speedlite to be key or fill.

    In summary, since the Slave AC Flashes are not designed for E-TTL, they are not compatible with the flash automation between the Canon 600EX-RT Speedlite and Canon Speedlite ST-E2 "Master/Controller", so your primary choice is to remove the ST-E2 from the system and run the 600EX-RT in manual mode.

    Moderator of the Cameras and Accessories forums
  • lynnmalynnma Moddess Emeritus Homosassa, Florida (Paradise)Registered Users, Retired Mod Posts: 5,163

    Thank you Ziggy for clarifying all this.. I knew you would.. It all makes sense. Thanks again.

  • pathfinderpathfinder Drive By Digital Shooter western IndianaSuper Moderators Posts: 14,496 moderator

    Hi Lynn, long time no see ;-)

    You can use a Canon ST-E3-RT Speedlite radio controller to control the 600EX-RT - works very nicely, but the other flashes will still be manual mode only, so....

    You can get a Yongnuo Speedlite YN600EX-RT II for Canon Cameras for about $120 bucks and it will be radio controllable with your 600EX-RT.

    Pathfinder -

    Moderator of the Technique Forum and Finishing School on Dgrin
  • lynnmalynnma Moddess Emeritus Homosassa, Florida (Paradise)Registered Users, Retired Mod Posts: 5,163

    Hi Pathfinder..Hope things are well with you

  • lynnmalynnma Moddess Emeritus Homosassa, Florida (Paradise)Registered Users, Retired Mod Posts: 5,163

    I don't know what happened with the rest of my thread.. it's missing.. I had said: thank you for your input and info on the speedlite. I was wondering already how I could move into another speedlite which would compliment my 600... you read my mind. Thanks :)

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