[jake14mw]

OK, I think I’ve done enough reading to understand triggering off camera flash using the wireless P-TTL mode in my K10d. My question now is, if you are using more than one wireless flash, how does that work? I understand that with one P-TTL wireless flash, the camera sends out a pre-flash trigger, and the flash does a pre-flash, measures the light, and adjusts correctly (I know this may be greatly simplified). What if you use two flashes wirelessly? How do they work together? I thought there was some way of selecting relative power between them? This leads me to another question, and maybe this is part of the answer: What is the purpose of the different channels? Thanks.

[mattdm]

OK, I think I’ve done enough reading to understand triggering off camera flash using the wireless P-TTL mode in my K10d. My question now is, if you are using more than one wireless flash, how does that work? I understand that with one P-TTL wireless flash, the camera sends out a pre-flash trigger, and the flash does a pre-flash, measures the light, and adjusts correctly (I know this may be greatly simplified). What if you use two flashes wirelessly? How do they work together? I thought there was some way of selecting relative power between them? This leads me to another question, and maybe this is part of the answer: What is the purpose of the different channels? Thanks.

You can use multiple flashes, but you can't, unfortunately, control them independently. The different channels are only so multiple photographers don't interfere with each other. Nikon really has us beat on this front.

[jake14mw]

Thanks for the reply. So if you use two together, will they think independently, and each put out enough light for proper exposure and therefore overexpose the picture?

[mattdm]

Thanks for the reply. So if you use two together, will they think independently, and each put out enough light for proper exposure and therefore overexpose the picture?

No, it's all calculated together and should "just work".

[jake14mw]

Wow, that's scary to me. This should not work any differently wirelessly vs. wired, right? I thought I remember seeing somewhere a Pentax diagram with multiple flashes wired in series. Does anyone have any more information on how this works?

I knew that Nikon had Pentax bested regarding the fact that in the Nikon system the power of each flash can be controlled from the camera itself, but I thought there was a way to set relative power levels on the Pentax flashes themselves. Sounds like maybe the only thing that could be done is to use the individual +- compensation on the flashes themselves? Maybe do a + on the one that you want as your main, and a - on the fill?

[RBellavance]

Sounds like maybe the only thing that could be done is to use the individual +- compensation on the flashes themselves? Maybe do a + on the one that you want as your main, and a - on the fill?

I recently bought a set of umbrellas and a 2nd flash, and that's the first thing I want to try out. If that doesn't work, I'll be quite disappointed.

Unfortunately, my 2nd flash was basically DOA, and I have to wait for it to be repaired or replaced (the store did not have another one in stock to exchange it...).

[jake14mw]

hmmmm.... from page 32 of the AF540 FGZ manual... Contrast Control Synch Mode - "This synch mode enables you to photograph with more than one flash unit, utilizing the difference of light intesity of each flash unit. The ratio of flash light intensity between the flash unit set to this synch mode and the other flash unit is 1:2." I guess this is what I was thinking of.

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Last edited by jake14mw; 08-31-2010 at 07:55 AM. Reason: typo

[jboyde]

When I use multiple flashes I have one be my main light and go TTL. The others I use EV compensation to go -2 to +1. The good thing is that you can also use the 540 (and most others) in PTTL mode and still dial in the power levels manually. Sometimes I do that when I know I'll need 2 or 3 stops extra light from the rear flashes to blow out my background to pure white but the Pentax flashes only go +1 (the Metzes go to +3 but thats a story for another day).
So this way you can use them as a sort of digital-ready slave units.

[Russell-Evans]

I knew that Nikon had Pentax bested regarding the fact that in the Nikon system the power of each flash can be controlled from the camera itself, but I thought there was a way to set relative power levels on the Pentax flashes themselves. Sounds like maybe the only thing that could be done is to use the individual +- compensation on the flashes themselves? Maybe do a + on the one that you want as your main, and a - on the fill?

There are two power output adjustments on the Pentax flashes when used wirelessly, FEC and a power ratio. FEC raises and lowers the power in stops. I don't really understand how the power ratio works. Either the flash knows about the multiple flashes and determines the over scene with the ratio in mind, or the flashes are independent and the power ratio simply overrides what the camera sends it.

You can also use the flashes in manual with wireless, (uses wireless channels and isn't a dumb optical slave), and set the output from 1/1 to 1/32, maybe lower on 540 but I don't own one so I don't know. There is also Auto flash available in wireless.

All in all the Pentax flashes are pretty full featured and offer a lot features other flashes don't, but they do require you to go to each flash to set those features up.

Thank you
Russell

[jake14mw]

In looking at Matt's guide again, it appears that the Contrast Control Synch method only works when the flash is wired, and not in wireless mode:

This is a Pentax flash system feature where a cable-connected flash fires in combination with the camera's built-in flash. The built-in flash provides one third of the required light and the off-camera flash provides the rest. Pentax and Metz supports this on their more advanced models, and Sigma on both models. This mode does not appear to be meaningful when using wireless P-TTL. In any case, setting flash-based exposure compensation can be used instead, for models which support that."

jboyde, thanks for the info. I'm still reading that trying to make sure that I understand it.

[mattdm]

In looking at Matt's guide again, it appears that the Contrast Control Synch method only works when the flash is wired, and not in wireless mode:

Let's be sure to leave open the possibility that I can be, and often am, wrong.

[jake14mw]

Let's be sure to leave open the possibility that I can be, and often am, wrong.

Well Matt, given that the Pentax manuals are not clear, your guide has turned into THE guide. So, it is now the standard reference! I saw one other thread where somebody said that it only worked corded also, but I'm not sure if he was just referring to your guide.

[jake14mw]

Russell, thanks for that information you gave. I thought that Jboyde was referring to Manual power settings, but were not sure, and your information was confirmation. I did not know that you could set the power level manually and still pick up the P-TTL trigger correctly to fire. That's good to know.

[Russell-Evans]

I saw one other thread where somebody said that it only worked corded also, but I'm not sure if he was just referring to your guide.

The contrast control only works only in wired mode, but wireless has that power ratio function that I don't understand. I tried to talk intelligently to a CS person on the live chat about it and his helpful response was to read me what was in the manual after I got him to the right page. Then when I tried to get a little deeper into understanding what was actually going on, he suggested that just to put the flash on the camera in P-TTL and it would just work. I thanked him for calling me an idiot and that was about it.

I no longer have two 360s to play with so the mystery of whether the power ratio works with or without the camera's knowledge will have to be answered by someone else. Really, manual mode seems much easier anyway.

Thank you
Russell

[GeneV]

The Pentax manual for the 540 is fairly lengthy but ambiguous. When it talks about being in contrast control mode with a ratio of 2:1, I've scratched my head about which flash is 2 and which is 1. I assume that you put one flash in contrast control mode and it is the lower powered.

If I'm using more than one flash (other than Wireless P-TTL with the built-in controlling) I usually just ditch P-TTL, flash in manual and chimp a few times untill the histogram looks good. Since some of my favorite portrait lenses won't work with P-TTL anyway, and it also allows me to pick up a film body, or even the 645, and shoot the same exposure.