firmware updated Cactus V6II does not control power of Pentax AF540FGZII

I have the following setup: Pentax K-3II (no built in flash); a Cactus V6II mounted on top; off camera a Pentax AF540FGZII on top of another Cactus V6II.  Both V6II's updated to V1.1.004.  I cannot get the Cactus RX to control the power output of the flash.  This is NOT about HSS; just normal power controlled flash triggering
I’ll trace the steps I use to try to get the Cactus V6II’s to control the flash.  Perhaps you’ll spot an error.
    My AF540FGZ II flash has all functions set to defaults (including Fn5:Slave mode #1 “When taking pictures in wireless mode” Note: I have tried option 2 as well without a difference.).  
    With both units turned off, I connect my flash to my Cactus while listening to the hot shoe for a “click” before locking the units together.  I connect my Pentax K-3II and a Cactus V6II the same way.
    I turn on the flash; it displays P-TTL.  
    I turn on the Cactus with RX.  The Cactus displays full battery, Ch 5, AF540F2, 1/8th, the Pentax flash icon, and the radio antennae icon showing strong connection. Group B button is on.
    I turn on my Pentax K-3II, Manual mode, 1/90th, f22, ISO100, 70mm lens.  With shutter half depressed, I turn on the Cactus in TX mode.  The Cactus displays full battery, ch 5, 1/8th under the B group and the B group light is on.
    Press menu on the Cactus, Function shows HSS OFF, other items off including TLL PASSTHROUGH.  Camera & Flash System = Pentax; flash Profile Pentax AF540F2.  Power Mode: I change from RELATIVE to ABSOLUTE (SETUP)>OK and the Cactus displays “1 flash found.”
    Press the test button on the Cactus connected to the  flash: Flash fires.  Press test button on camera Cactus: Flash fires.  I adjust power settings on the Cactus TX.  Settings transfer to flash Cactus.
     With EV9.5 (lowest setting) I take picture of wall hanging.  Get a slightly under exposed image.
    I change the EV to 16.5 (highest) which the flash Cactus shows.  I take a picture.  The exposures are identical.  It would appear that the on-flash Cactus does not communicate power setting to the flash unit.
    As you might guess, I have played around with all sorts of settings without success.  The above outline is how I think the units should work.  But they don’t.
    As an aside I also have a Cactus V6–upgraded to make it compatible with the V6II.  Altho I have not tested this pair as extensively, I think the same problem exits.  Could the Cactus V6II upgrade be faulty?
   Any ideas?


  • I separately sent a note to Cactus about this problem and they had a surprising solution.  Even though in this example I am NOT using HSS, I needed to set my flash to HSS.  Apparently the Pentax HSS protocol is what Cactus uses to communicate with the flash even if HSS is not used.
  • Thanks @seriaphoto for posting your observation! :)
    Antonio Lao
    Brand Manager

    To help us better help you, always state the exact firmware version installed on your Cactus device(s), such as: "1.1.013", "NIK.A.001", "v.103", or "A06".

    TTL or HSS not working on Cactus V6 II and V6 IIs? Be sure to check hot shoe connectivity by doing the <CAMERA INFO> check.

    Feel free to suggest an improvement or share product ideas. Contact us directly at  At Cactus, we listen. 
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