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02-25-2010, 07:21 AM   #1
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Cactus V4 + Pentax flash + cold = :(

I know this is long, but please bear with me...

I've been using a Cactus V2s trigger for a while, and decided to upgrade to the newer V4 model. So I placed an order with Midwest Photo Exchange and I received my one transmitter and two receivers yesterday. The first thing I did was set up my two AF360-FGZs and test them out (inside the house). They worked reliably at the maximum sync speed, and I was happy. Then I decided to put them to some real use. I went out to catch some snowflakes for macro shots.

My setup involved one of the receivers and one AF360 flash. I got everything set up in my open garage (about 25 F, -4 C), grabbed the sheet of glass I use to catch the flakes, and spent a few minutes waiting for some good ones. By the time I returned my "slide" to the "studio", I noticed that my first couple shots came out completely black. I thought that was quite odd, because I saw the flash firing. I quickly realized that it must be missing the 1/180 sync in X mode. No problem, I dialed it down to 1/100. No luck; still a black frame. 1/30...still dark. 1/15...now it worked! I could only think to myself, "WTF?! They worked fine an hour ago!"

I brought the photo gear back inside, and compared the non-functioning flash/transmitter combo to the other pair. The one I had left in the house worked fine, the one I took outside still didn't sync. I took the good one outside and attempted another shot. By the time I captured another good flake, it also didn't sync anymore. Ah ha! It must be the temperature! These Cactus triggers don't like cold. I checked the interweb, and it appeared to be a known issue. Problem solved...or so I thought.

Curiosity got the better of me and I decided to run a controlled test to understand the limitations of the Cactus triggers. I stuck a receiver flash combo in the freezer for a while, and took it out for a test fire. Using an infrared thermometer showed a surface temp of 5 F (-15 C). I also had one identical AF360/receiver sitting at room temperature. Not surprisingly, the cold one didn't work and the warm one did. But then things got interesting. I swapped flashes on the receivers, so now I had a warm flash/cold receiver pair and a cold flash/warm receiver pair. This time, neither one worked!

So now I coudln't decide if it was the flash or the receiver. Seems like either one being cold was causing a problem. So I decided to eliminate some of the interactions. I put my other strobe, a Nikon SB-28, on the Cactus V4 receiver. I then put an AF360 on my Cactus V2s receiver. Both of these asemblies went in the freezer for a while. I took these ice cold puppies out of the freezer and tested them. Both worked immediately at 1/180!

Along the way, I also tried to elminate other factors. I learned that it's not the batteries in any of the units. I put fresh, warm alkalines in the Cactus receivers when they were cold. I put freshly charged, warm Eneloops in the Pentax flashes when they were still cold. I put warm alkalines in the Pentax flashes while they were still cold. I eliminated the transmitter as part of the problem, after repeating the above tests with the camera and transmitter straight out of the freezer. In all cases the performance was the same.

The other interesting thing is that if I took a picture of the frozen V4/AF360 combo, the red light on the Cactus trigger would be lit in the 1/180 exposure, even if the flash was delayed and the rest of the frame dark. I don't know what to make of that. It's like when the hot shoe on the Pentax flash gets cold, the flash is slow to sync (even when the rest of the flash is warm). But the same problem doesn't happen with the Cactus V2s, so I'm just back to being confused. My next step is to try to find out the threshold temperature at which the sync speed becomes a problem. I hope it's more like 30 F and not like 60 F .

So the Cactus V4 doesn't hate the cold. And the Pentax AF360 doesn't hate the cold. But put them together in the cold, and they don't sync fast enough. Any ideas what could cause such behavior? It would seem that I've just run across a peculiar interaction that limits what I can do in the cold. I'll just have to use the Nikon flash or be content with syncing at 1/15 when I use them in chilly weather.

02-25-2010, 08:18 AM   #2
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I've had the same problem.

I too have two Cactus V4 receivers and and two AF360-FGZs (actually one and a Samsung SEF-36PZF which is all but identical. I use a K20d).

About half the time the flashes sync at 1/180 perfectly. At other times the flash fires too late, not syncing until 1/15. As before, If I take a photo of the receiver, the red light is on but not the flash. Sometimes it is even possible to hear the two flashes, triggered by the same transmitter, firing at slightly different times.

I haven't tested if the temperature affects this, but the last time it happened I was outside (temperature approx 5 C). They were working normally for a few minutes nad then moved to 1/15 sync.

Sometimes the problem happens indoors too.

I bought mine from GadgetInfinity who offered an exchange, agreeing they seemed faulty, but I haven't sent them back. I want to try them on a non-Pentax flash first.

Mike

Last edited by marnold; 03-04-2010 at 01:19 AM.
02-25-2010, 09:09 AM   #3
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Yes, and V4 with old Pentax flashes like AF280T and AF200T in cold is fine, I put them in the snow ( yes under the snow) and they sync great


Only not good when i put the 540fgz and V4 together... it is a common problem and I think GadgetInfinity don't know about it as they are in Asia where always enjoy the warm weather so didn't really able to test it when they are producing them. The main reason I heard from other is that the trigger voltage is so close to what the battery can offer, so when V4 is in the cold, battery can't push enough to make the flash sync fast enough.. don't know if it is true or not.
02-25-2010, 09:09 AM   #4
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try using the pc sync to the transmiter and also check if you have your on camera flash set to normal if its on wireless you will get a delay because of the pre flash

02-25-2010, 10:31 AM   #5
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Thanks marnold and vizjerei. It's good to see a little confirmation that I am not, in fact, crazy. I was starting to suspect it maybe a low trigger voltage issue. Perhaps the trigger voltage of the new Pentax flashes is so low that it just barely works at room temperature. Then, if the resistance through the trigger circuit goes up much when it gets cold, or the voltage drops much in response to the temperature, it could move the flash over the threshold from "barely able to sync" to "just barely unable to sync" rather easily. I wonder if there would be any way of modifying the system to give a little more margin.

And clarence, thanks for the suggestions. But the flash mode isn't the problem. It works fine one moment, but then fails when temperature changes even without changing any settings on the camera. But to be sure, I did check that I was in regular flash mode, and not wireless. I also don't think I'm seeing any problems with the transmitter lagging...as I mentioned before, I can always capture the confirmation LED on the receiver at any sync speed and any temperature. But sometimes the actual flash pulse lags long enough that I need 1/15 sec to capture it. It's defintiely a trigger delay and not a transmit/receive delay.
02-25-2010, 07:03 PM - 1 Like   #6
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UPDATE: PROBLEM SOLVED

...And all it took was a soldering iron. I scoured the forums, and came to learn that the Pentax 540 and 360 flash units have a particularly low trigger voltage. I measured mine to be 3.05 V on each one, while my Nikon SB-28 measured 4.45 V. The trigger circuit of the Cactus triggers contains a rectifying diode to handle flashes of different polarities (though all modern flashes should be the same, with a positive center pin). This diode created a voltage drop, probably about 0.7 V, that takes the already-low flash voltage down to near-unusable levels. Add a little extra voltage drop from the cold temperatures, and the combination starts giving the slow sync problems.

So, what's the solution? Just bypass the rectifying diode and reclaim that 0.7 V, because the Pentax flashes need all the margin they can get. The only downside is that you can never use the Cactus triggers with a reverse-polarity flash, which you'll probably never lay hands on anyway.

To do this, I just soldered a jumper wire between the negative battery terminal and the connection point for the hot shoe ground plate. The pictures below show the back of the receiver unit covered for orientation purposes, the same unit uncovered before the fix, and uncovered after soldering the jumper wire in place. Finally, a close up of that wire and the contacts it's connected to.

After making this fix, and testing functionality at room temperature. I then stuck the AF360 and V4 combo in the freezer again for half an hour. Then I took it out and checked for 1/180 sync. I was excited to find that it works beautifully now. Temperature is no longer an issue for these guys.

If you know how to use a soldering iron, this will take you all of 5 minutes. It's super easy, potentially reversible, and worked like a charm for me on *both* of my temperature-sensitive units. Personally, I had no worries about taking a soldering iron to these. Sure, I could have returned them, but when I looked at what I'd have to spend to get something more professional, I decided it was worth the slight risk. If I broke the first receiver, or the fix didn't work, I could still have sent one complete transmitter and receiver back without modification.
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02-25-2010, 07:20 PM   #7
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wow thanks I will try it out, hope that finally I can use my 540fgz and cactus together in the winter time!
02-26-2010, 12:15 AM   #8
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This is awesome! I brought this problem up a while ago but came to no conclusion of how to fix the problem. We've had quite a cold spell here in Sweden these past couple of months also so they've just been lying in my other bag that I didn't take out with me.
Now I have two reasons to find that darned soldering iron...*mumbles something aobut the closet being too big*

vizjerei: Thanks for the link!

02-26-2010, 12:17 AM   #9
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This should almost be a sticky or put in the DIY articles section!
03-08-2010, 09:52 AM   #10
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I've soldered as instructed and bypassed that little diode and it works like a charm!
Thank you for looking into the matter and finding such an easy solution!
03-09-2010, 01:42 PM   #11
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Really glad to hear it worked for you. It's definitely an easy fix, and makes the new Cactus triggers a lot more reliable with our Pentax flashes.
03-10-2010, 09:30 AM   #12
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I still need to ask my Dad where did he put his soldering iron, then I will crack open all 3 of the receiver. Thanks again, aerodave
03-10-2010, 10:15 AM   #13
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Good luck! But this reminds me that I should probably take this opportunity to add a disclaimer to anyone intereted in following my lead:

I am not an electronics engineer. I am not a genius with a soldering iron, and I can just barely read an electrical schematic. Transistors confuse and frighten me. You follow my example at your own risk. This is a pretty simple job, and there's no reason to think it's not as close to idiot-proof as anything which requires soldering can be.

I undertake exercises like this because I'm generally not afraid to break things I own for the sake of learning something. Most of the time it works out, but I'm prepared for those times when it doesn't. Please only attempt to follow how-tos you find on the internet if you share the same philosophy. If you break your toys, I didn't make you do it. And for the record, PentaxForums.com didn't make you do it eaither.

Now go forth and hack some gadgets!
03-10-2010, 01:55 PM   #14
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And the mandatory minimum text length.
03-17-2010, 08:54 AM   #15
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Just did that to all 3 of mine~ finally I can use my 540fgz in the cold now~ Thanks again!
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