Light meter and pre-flash

edited February 2019 in V6 II Suggestions
Hi, everyone,
I have a little concern with my equipment:

Pentax K-1
Pentax AF540FGZ II
2 x Cactus V6 II
Sekonic L-308X

I would measure contrast of light with my light meter, but the flash shall work in P-TTL mode and it shoots a pre-flash, which cheats the light meter. Now I have to switch my flash on "M" mode and set the power directly on its body. Is it possible to design a test mode on the V6 II, with pre-flash disabled?


  • Thank you for the suggestion. I'll discuss with our engineering team for the possibility.
    Ray Chan

    Senior Product Specialist
    Harvest One Limited
  • edited February 2019
    Thank you. I've read that it is a common problem with transceivers and TTL flashes. Only some high-priced light meters are capable to ignore pre-flashes. On my L-308X if find a solution: measuring the flash with shutter speed 1/15 s, it is able to see both the pre-flash and the main flash.
  • That's brilliant.
    Ray Chan

    Senior Product Specialist
    Harvest One Limited
  • edited February 2019
    That's a quick fix ))
    That works using the V6 II test button.
    Triggering via camera shutter button, on the L-308X you have to set a reading time equal to 1/8 s. Such method is appliable only in indoor shootings, where ambient light is unimportant compared to the flash.
  • Hi, everyone,
    did engineering team find a solution with these pre-flashes? Such problem makes the use of external exposimeter impossible when shooting outdoor, I should use a cheap set of triggers instead of V6 II.
  • edited May 2019
    I've tried to activate flash with my camera thorugh the mirror up exposure, and effectively at the first press of the shutter the pre-flash bursts, but the main flash doesn't. Maybe it will work with rear curtain sync.

    But I'm searching for a methot to test the flash without pressing shutter, because I want to shoot with film camera also.
  • edited November 2019
    Hi, everyone,
    meanwhile I've find the final solution to many problems:

    In my experience Pentax flashes are intended to be used on Pentax cameras only, foget the TTL pass-through.

    First of all Pentax AF540FGZ II, a flash for 500 $, has a crappy hot shoe lock (it's entrusted to a very fragile tooth running in a groove), that perhaps will not break if used on a Pentax camera, but it will in few months if mounted on a Cactus V6 II, because the thicker rim of the V6 II's hot shoe mount and the resulting higher stress.

    Because of Pentax pre-flash, that works even in manual mode (it's an artificial manual mode, the flash must always be set in P-TTL) is not possible to make measurements with a lightmeter.

    Trying to trigger a Pentax flash causes myriad of other problems, that I'm not about to list.

    Using two V6 II in combination with an expensive Pentax flash is an useless waste of money, I recommend to buy only one Cactus V6 II and one or more Cactus RF60X, such ensemble will work perferctly both in manual mode and TTL.
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