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11-08-2017, 09:50 AM   #1
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Bowens Prolite 120 and the Pentax K1

I was given this amazing flash, c. 1993 but mint condition - looks like this



I am using it with a reflector and an umbrella and the results are great. It is massively powerful so I am using it on minimum power.

It can be cable triggered or work as a slave flash. I measured the open circuit voltage on the trigger cable at 14V so this is not one of the old Metz45 variants with a 150V+ voltage which destroys cameras

The flash came with a long trigger cable which is terminated on the standard miniature coax plug.

It works fine with the cable going direct to a hotshoe adapter on the K1



but it doesn't work via a RF602 radio link



even though I have checked with a meter that the receiver does act as a relay contact, on the hot shoe shown.

Another way might be a cable from the RF602 receiver (as the one shown above but with a 1/4" jack plug on it) but I don't have one and can't see one for sale. But that may not work either because I bet the receiver cable is just wired to the hotshoe contact.

Is there a radio trigger which is likely to work from the K1 to the Bowens flash?

Also doesn't the K1 have an internal radio transmitter which could be used?

11-08-2017, 10:40 AM   #2
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QuoteOriginally posted by peterh337 Quote
Also doesn't the K1 have an internal radio transmitter which could be used?

I can just answer that last one, which is "No". There is no in-built Wireless flash capability on the K1.
11-08-2017, 12:40 PM   #3
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Triggering these lights with a Yongnuo RF603 trigger/receiver with a Jack lead into the Prolite will work perfectly. I have fired mine for many years this way...

The Wansen PTY-16 triggers also work very well.
11-08-2017, 01:38 PM   #4
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Which RF603 would you suggest? They seem to do about 10 variants. Also it now looks like the transmitter and receiver look the same. Also I wonder whether the 1/4" jack adaptor is anything special. I think I got one with the RF602 but can't find it anymore.

Edit: I think I have found one: https://www.amazon.co.uk/YONGNUO-DIGITAL-LS-PC635-STUDIO-FLASH-Black/dp/B007KA3LQS


Last edited by peterh337; 11-08-2017 at 02:12 PM.
11-08-2017, 05:47 PM   #5
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In the Yongnuo both receiver and trigger do look the same. "RF603II C1" Remember the cable will also have to 6.3mm Jack adapter to fit the Prolite connection..

The Wansen trigger is also good as it can be attached to the Prolite mounting bracket. (It has a very convenient hole drilled in it )

---------- Post added 08-11-17 at 05:54 PM ----------

WANSEN PT-16GY 16 Channels Radio Wireless Remote: Amazon.co.uk: Electronics

SODIAL 3.5mm to Male PC Flash Sync Cable Screw Lock for: Amazon.co.uk: Electronics

HDE Metal Hot Shoe 1/4"-20 Thread Screw Post Converter: Amazon.co.uk: Electronics
11-09-2017, 02:11 AM   #6
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I ordered the 1/4" cable initially, in case the RF602 works with it. If it doesn't I will order the RF603.

Incidentally I wonder why nobody has developed a compact hotshoe mounted master flash unit for triggering flashes, and for sending the data to slave flashes. It would use LEDs, not a flash tube.

I have that SODIAL cable (your middle link above); it came with the RF602. In fact about 3 of them, with a diffing number of poles on the 2.5mm or 3.5mm jack plug. One of them is for use as a remote camera shutter trigger (the K1 takes a 2.5mm 2 pole plug, IIRC) and I have used the RF602 mainly for that and it works fine (for astro work or any other "B" mode work, it is desirable).
11-09-2017, 07:04 AM   #7
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RF602 will work perfectly.. I just stated RF603 as its the latest model... The Yongnuo triggers are just more difficult to attach, as they have no screw thread underneath. Like the Wansen receivers. So are usually just left dangling from the jack point...

Last edited by stub; 11-09-2017 at 06:46 PM.
12-26-2017, 02:06 AM   #8
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No luck so far. I bought the 3.5mm to 1/4" adaptor shown here and nothing happens...



The receiver works fine (with a different cable) as a remote trigger for the K1, and every other Pentax I have had.

12-26-2017, 07:58 PM   #9
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That set up should work.. !! Make sure the sender battery is fully charged..
12-28-2017, 01:32 AM   #10
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The TX+RX do work. I just change the cable and can trigger the K1 with it.

The flashgun needs a short across the two jack terminals to make it flash (a screwdriver is the traditional method ) and for some reason the RX here is not doing it.

I will rig up a pullup resistor with an oscilloscope to narrow it down but I suspect the RX cannot pull down sufficient current, or isn't pulling it down for long enough.
12-29-2017, 02:06 PM - 1 Like   #11
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I did some tests and the RF-602 is not capable of pulling down more than about 2mA. If you try to make it pull down more than that, it latches up and stays pulled-down.

The Prolite has a 14V open-circuit voltage and that wasn't an issue. I found that its internal pullup sources 110uA. Crucially I also found that to trigger it you have to pull it down with a resistor of 56 ohms or less. 100 ohms won't trigger it. What this means is that whatever is used to pull it down has to go down to something like 6mV or less. This is unlikely to be achieved with a bipolar transistor, due to Vce(sat) of these being of the order of 100mV. The simplest way is a MOSFET because they are just a resistor.

So I built this little circuit, which I hope somebody finds useful. It is powered via the flash's 14V pullup. When the jack plug is first plugged into the flash, the 470uF capacitor has to charge up, so you get a spurious flash. Apart from that it works perfectly. I later dropped the capacitor to 100uF (20V rated).



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