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10-24-2009, 05:09 AM   #1
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HELP -- TTL flash not triggered by radio triggers

I have a Pentax Compatible TTL Centon FG105D Flash which works fine on the camera hot shoe. In fact, I'm surprised how well it works: Changing the focal length on a zoom will automatically adjust the motorised flash zoom, the aperture information is transmitted, etc. Shame that my K100D cannot make use of the flash's TTL functionality.

Here's the problem: I just got a Cactus V4 radio trigger set and it works without problems with my Vivitar flash.

The Centon, however, must be one of those flashes which are not compatible with radio triggers. I cannot make it fire by shorting the main hot shoe pin with the side contact (works with the Vivitar).

Does anyone know how such flashes are triggered by the camera if not by shorting the main hot shoe pin with the side contact?

Does anyone have an idea how I could modify the flash so that it can be triggered by the radio triggers?

Unfortunately, the Centon doesn't have an additional trigger socket. If everything else fails, I might try to add such a trigger socket that will connect to the test button of the flash. That may not work though, as someone has found while modifying their Sigma EF-500 DG which cannot be triggered the normal way either. In the case of the Sigma flash, using the test button introduced an unacceptable delay.


Last edited by Class A; 10-25-2009 at 02:30 PM.
10-24-2009, 06:37 AM   #2
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QuoteOriginally posted by Class A Quote
I have a Pentax Compatible TTL Centon FG105D Flash

Here's the problem: I just got a Cactus V4 radio trigger set and it works without problems with my Vivitar flash.
The flash you have is the same as the Promaster 7000m and Quantaray PZ-1 DSZ in the US. The Pentax version of this flash will not work with any trigger I have tried. My only suggestion is to use the flash in the optical slave mode and have it triggered by another flash that will work with the remote trigger.

If you can find a deal on the Nikon version of this flash, it will work with the triggers without issue. I have been pretty successful in picking up the Nikon version for under US $20. For shorter distances, having the Pentax version on the camera and Nikon version in the optical slave mode also works very well, so it isn't like having the Pentax version is a bust.

I bought the Minolta version of the flash for a few dollars. This version has the non standard mount so I bought a converter to try it on a radio remote, This didn't work. The Minolta doesn't have the simple optical slave mode either. It has a wireless function that only works with other flashes in that system. Now that was a dead end.

Thank you
Russell
10-24-2009, 04:43 PM   #3
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QuoteOriginally posted by Russell-Evans Quote
The flash you have is the same as the Promaster 7000m and Quantaray PZ-1 DSZ in the US.
Very interesting to know, thanks.

QuoteOriginally posted by Russell-Evans Quote
The Pentax version of this flash will not work with any trigger I have tried.
Yes, this is caused by the fact that it doesn't fire when one shortens the centre and side pins of its hot shoe.

The Pentax version seems to be different to most others since I've seen people report that they successfully used their Promaster FTD 7000M or their Quantaray PZ-1 DSZ with radio triggers.

QuoteOriginally posted by Russell-Evans Quote
If you can find a deal on the Nikon version of this flash, it will work with the triggers without issue.
Interesting, thanks again.
Unfortunately, it is unlikely that I'll find one of these or another suitable one here in New Zealand with its tiny market.

Perhaps I can trade in my Pentax dedicated version with a Nikon version of a forum member with an *ist camera who could make full use of the TTL capabilities of this flash.

QuoteOriginally posted by Russell-Evans Quote
I have been pretty successful in picking up the Nikon version for under US $20.
Wow, I paid a lot more for my Pentax version.

Still interested in learning about a potential modification to the flash. It should be possible one way or the other.

Last edited by Class A; 10-26-2009 at 04:08 AM.
10-25-2009, 02:34 PM   #4
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Does anyone else have a flash that cannot be triggered by shorting the centre and side contacts of the hot shoe pins?

10-26-2009, 04:06 AM   #5
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I've just did a few experiments to figure out what makes the flash fire when it is on camera.

Result: The only contacts required are the "digital" and "trigger" (aka SYNC) contacts, plus "ground" obviously. The flash will not fire with "ground" and "digital" only.

That implies that the flash is triggered through the centre trigger contact but only if it enabled the latter by having received some data through the "digital" contact first. Hence, it seems unlikely that the flash can be made to fire unless on piggy backs on either the "test button" or the "optical slave sensor".

Last edited by Class A; 10-26-2009 at 04:13 AM.
10-26-2009, 04:11 AM   #6
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If you have a Cactus receiver with a PC socket then all you need is one of these

Kaiser | PC to Hot Shoe Adapter | 201301 | B&H Photo Video

QuoteOriginally posted by Class A Quote
I have a Pentax Compatible TTL Centon FG105D Flash which works fine on the camera hot shoe. In fact, I'm surprised how well it works: Changing the focal length on a zoom will automatically adjust the motorised flash zoom, the aperture information is transmitted, etc. Shame that my K100D cannot make use of the flash's TTL functionality.

Here's the problem: I just got a Cactus V4 radio trigger set and it works without problems with my Vivitar flash.

The Centon, however, must be one of those flashes which are not compatible with radio triggers. I cannot make it fire by shorting the main hot shoe pin with the side contact (works with the Vivitar).

Does anyone know how such flashes are triggered by the camera if not by shorting the main hot shoe pin with the side contact?

Does anyone have an idea how I could modify the flash so that it can be triggered by the radio triggers?

Unfortunately, the Centon doesn't have an additional trigger socket. If everything else fails, I might try to add such a trigger socket that will connect to the test button of the flash. That may not work though, as someone has found while modifying their Sigma EF-500 DG which cannot be triggered the normal way either. In the case of the Sigma flash, using the test button introduced an unacceptable delay.
10-26-2009, 04:18 AM   #7
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QuoteOriginally posted by *isteve Quote
If you have a Cactus receiver with a PC socket then all you need is one of these

Kaiser | PC to Hot Shoe Adapter | 201301 | B&H Photo Video
Thanks for the suggestion Steve, but it won't work, will it? The Kaiser PC to hot shoe adapter doesn't do anything else than shorten the (centre) SYNC contact to (the outer) ground. It would not send any signals via the "digital" contact to the flash prior to that. The latter, however, is required with a few flashes which won't fire just by shorting their centre and side hot shoe contacts.

What made you think the adapter will make a difference?

Last edited by Class A; 10-26-2009 at 04:28 AM.
10-26-2009, 11:56 AM   #8
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QuoteOriginally posted by Class A Quote
Thanks for the suggestion Steve, but it won't work, will it? The Kaiser PC to hot shoe adapter doesn't do anything else than shorten the (centre) SYNC contact to (the outer) ground. It would not send any signals via the "digital" contact to the flash prior to that. The latter, however, is required with a few flashes which won't fire just by shorting their centre and side hot shoe contacts.

What made you think the adapter will make a difference?
Sorry, my bad, didnt read the intervening posts properly.

I have only tried Pentax flashes and they trigger OK with the Kaiser. Didnt reallise some 3rd party makers check for the TTL pin as well (or more likely lack the logic to assume its "off" if its not enabled).

Bummer. This is how I trigger all my off camera flashes using Skyports. Guess I wont be buying 3rd party flashes.

10-26-2009, 01:58 PM   #9
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QuoteOriginally posted by *isteve Quote
This is how I trigger all my off camera flashes using Skyports. Guess I wont be buying 3rd party flashes.
Flashes that can be fired with the Kaiser adapter will fire on the Cactus V4 receiver directly.

I don't think you need to avoid 3rd party flashes as a rule. The vast majority will work and to the best of my knowledge there are only a handful of exceptions.
10-26-2009, 08:44 PM   #10
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QuoteOriginally posted by Class A Quote
Flashes that can be fired with the Kaiser adapter will fire on the Cactus V4 receiver directly.

I don't think you need to avoid 3rd party flashes as a rule. The vast majority will work and to the best of my knowledge there are only a handful of exceptions.
Well, the only other ones I am likely to use are Metz and I think they are OK.
11-24-2009, 04:53 PM   #11
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Inspired by a modification someone did to their Sigma EF-500 DG I decided to add the ability to be triggered by a radio trigger to my Centon FG105D flash.

In the first image below you can see my dismantled Centon FG105D. One only needs to unscrew four screws to open it and a further two to get at the focus light / flash sensor component (big thingy at the bottom). It turned out that I didn't even need to loosen the board with all the electrical components on it.

Name:  centon-cables.jpg
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Size:  69.1 KB

At the board I marked the two cables that lead to the flash sensor. First I intended to solder wires to these positions but then ended up soldering my two wires to the flash sensor (marked as well) directly. These two extra wires need to be soldered to a female jack (marked in the bottom right corner of the image). The female jack is a standard 3.5mm headphone jack which I nicked from an old radio.

The second image shows how I integrated the jack (right marker) into the bottom part of the flash and where the wires from it go to (left marker).

Name:  centon-jack.jpg
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Size:  65.4 KB

When I now attach my Cactus V4 trigger to the 3.5mm connector cable that comes with every receiver and then connect the latter to the flash, the flash will fire every time the receiver triggers. Of course I need to set the flash to the optical slave mode.

The optical slave function still works. If I ever find the need for it, I may add a switch to be able to turn it off in case I don't want other flashes to trigger the Centon.

The modification was really easy to do (don't make it your first DIY project, though) and triggering now works like a charm with 1/180 sync speed without any problems whatsoever.

If you are interested, you can view the modified flash in action.

Last edited by Class A; 11-26-2009 at 03:40 AM.
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