A question on Slave mode "2"

I am trying to use three flash guns.

I have two AF 540 II units and one AF 360 unit. I have three Cactus V6II triggers. The 540s are triggered by a Cactus V6II each in Rec mode and the third V6II is in Tx mode on the camera hotshoe.

The AF360 i have set to Manual mode and set the slave mode to "2". When i take a picture all three units fire, but the AF360 is not adding any light to the picture. I can see its light output on the subject through the viewfinder as I take the picture so it seems to me it must be triggering very late and the mirror has already returned by the time it is providing its flash.

Anyone else experienced a similar problem when using a mix of radio triggers and "dumb flash mode 2"

I am using Manual mode on my K1, 1/180 f11. The two AF540s are set in normal P-TTL mode (as per the Cactus manual for the triggers). The AF360 is set to Wireless slave mode; Slave mode 2; and manual exposure flash output.

Hi Peter, I believe the V6IIs use aspects of the P-TTL protocol, and as such they cause a pre-flash to be generated from the AF-540s. This means that the 360 slave flash cannot sync with them... It is firing before the exposure occurs.

There is no functional purpose at present to the pre-flash. Eventually it will be utilized for metering purposes once the V6IIs get their 'TTL without boundaries' upgrade.

But the incompatibility with Pentax's SL2 mode will remain.

Thanks Nigel

So I guess I am seeing its flash before the mirror lifts. Oh well if I want to use three flashes I shall have to get another Cactus trigger. Getting expensive this flash malarky! But I am really enjoying the new adventure.

Would it not work if all three flashes are set to manual - so no pre-flash? Then just set the power output on each to get the effect you want.

Hi Philip

Yes that would work if i were not using radio triggers. The Cactus triggers require the flash units it is controling to be set to P-TTL, even though I am using manual control for them.

I am finding the convenience of being able to change individual power settings and zoom settings from my shooting position via the Tx unit to be much more convenient than having to change settings on the flashes themselves. So my only option is to get another trigger if I want to use three flashes and keep radio control.

Yes, the Cactus triggers use some technical electronic component of the P-TTL protocol in order to gain remote control over the power levels .... This cannot be achieved with the flashes in manual.

This pre-flash situation is also a new thing with the V6II .... The previous original V6 model does not cause this, as it is a single pin model with no communication of any P-TTL electronic information. Although P-TTL is still required for the mode on the receiving slave flashes, this does not cause a pre-flash. So in my case, with a single V6 and RF60 flash, I can use both of my Pentax flashes in SL2 mode, triggered optically by the RF60.

Another option Peter, at least to get use out of your third flash, is to use it on top of the V6II transmitter, in 'TTL Passthrough' mode .... An on camera flash used like this can be very useful, mainly as a bounced fill light, aiming it at a wall or corner to your side or even behind. It will automatically sync with your radio transmitter in either P-TTL it M modes.

Regarding the extra expense ... Think positive! Soon, once the firmware update comes, you'll have 3 radio controlled P-TTL flashes, with automatic metering, HSS, 2nd Curtain etc .... You'll be one of a very select bunch!

Hi Nigel, select bunch indeed, I hope my dogs appreciate my efforts on their behalf !

I have tried the flash mounted on top of the Cactus TX on the camera but a practical issue arose which caused me to ditch the idea pretty quickly. With the flash fitted with a gary fong diffuser the weight was causing a slight wobble despite everything being locked down tight. This would lead to the TX unit losing contact and not triggering at all at times. I will try again at some point with another of the units as TX and seeif it makes a difference.

About TTL Passthrough.....what would be the advantage of using that mode rather than manual on the on-camera flash?

The TTL passthrough is a V6II mode that allows normal flash to camera communication to 'passthrough' the transmitter. The flash and camera will behave as if there was no V6II and the flash was directly on the hotshoe. You can operate the flash in any way just as if it was .... So you can choose P-TTL, Manual, HSS, 2nd curtain etc.

You are probably not being firm enough .... The locking lever on the Cactus goes around a long way and probably needs more tightening. I would suggest that un-diffused bounced flash, with a high angle and reflecting fill light back from a wall, would be preferable to a Fong diffuser, which will throw too much light all over the place.

Ok thanks I will give the bounce idea a try

i did read the manual about TTL passthrough and was a little confused. So the "passthrough" only affects the on camera flash? So i could in theory use the on camera flash in P-TTL even though the off camera ones were in manual ?

I will give it all a try at any rate. Thanks again

That's all correct Peter. The on camera flash can work automatically with P-TTL mixed in with manual output from the radio triggered flashes. I do this sometimes, it works fine, although equally it may be more intuitive to go manual on all flashes. We might expect the on-camera flash to underexpose in P-TTL with your system however, because the camera will detect the pre-flashes from your off-camera flashes as well, fooling it into thinking there is more power than there really is.