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Cactus PT-04/Cactus V2 wireless radio-based flash trigger. DonationsCopyright © 2007 NK Guy

The Cactus PT-04 flash trigger, also known as the Cactus V2, is a very low-cost radio remote system for firing hotshoe or PC-connected flash units wirelessly.

It consists of a transmitter/receiver pair housed in inexpensive black plastic enclosures. Each unit is about the size of a small box of matches. The transmitter fits into a camera’s hotshoe and the receiver clips onto the hotshoe base of a battery-powered flash unit.

Trigger photo

The picture above includes a UK 10p coin for scale. The coin is roughly the same size as a Canadian or US quarter or a 1 euro coin.

Operation is very simple. Turn the receiver on by sliding over the power switch, and then take a photo. That’s it. A radio signal is transmitted from the transmitter to the receiver that instructs the flash to fire.

The product is made in Hong Kong, China, and I bought mine from an eBay retailer trading under the name "gadgetinfinity". They have their own Web site where they sell a wide range of camera accessories (mostly low-cost clones of popular devices), but note that while their eBay prices tend to be lower than those on their own site, they make up the difference through increased shipping costs. It appears that Gadget Infinity is owned by the manufacturer of the product; Hong Kong firm Harvest One Limited.


The transmitter is a small rounded box with a hotshoe foot on its base. The foot has a rotating ring so the box can be fastened tightly to the camera’s shoe. (this is actually an important point to note - I also have a different flash trigger device which has a hotshoe with no tightening ring, so it just fits by friction!)

The transmitter also has a red LED that illuminates when a shot is taken, a small test pushbutton for test firing, a DIP switch block with two switches and a 3.5mm (1/8") phono socket.

Since the switch block has two switches with two positions each, a total of 4 digitally encoded signals are possible. The receiver will only trigger if both devices are set to the same code. Somewhat confusingly, the blue switch block has "O N" and "1 2" printed on it, which may lead some people to think that the switches are used for turning the transmitter on. They aren’t. The transmitter does not have a power-on or standby switch, since it’s always off unless fired by either the test button or by the hotshoe or the input cable.

The 3.5mm phono socket is used for external triggering of the device if you want. The transmitter ships with a short 2.5mm phono to male PC connector cable, so if you’ve got a camera with an X sync connector but no hot shoe (like a lot of older cameras from the 1960s and 70s) you can still use the device. Most people won’t need this cable, however. This sort of flash work is typically done with digital SLRs, which have hot shoes.

The transmitter is powered by a 12 volt alkaline battery, type L1028 or 23A, of the variety used in smoke detectors and keychain remotes and the like. It’s accessible by removing a small Phillips screw which keeps the halves of the transmitter shell together.

The unit sends out radio signals indiscriminately (the devices aren’t paired up or anything like that), and so you can have as many receivers scattered around as you like. As long as the receivers are all set to the same code then you’re OK. According to the eBay seller the unit transmits at 433 MHz. The box and transmitter are marked with the CE logo, and the manufacturer have stated that the products have the necessary certifications for legal use in the European Union. At this time they do not have approvals for other countries (eg: Industry Canada, Australian Communication Authority, etc) though the manufacturer have stated that they are in the process of obtaining FCC approvals for the USA.


The receiver is a small rectangular plastic box with a chamfered top. It has a hotshoe mount for attaching a standard battery-powered hotshoe flash unit, and an extruded aluminium L bracket screwed to the side which can be used for attaching the trigger and flash to a stand or tripod. The black-painted L bracket, which can be rotated to tilt the flash, is fastened to the box with a plastic-handled bolt. It also has a 1/4-20 hole for screwing the unit to a tripod via a normal mounting stud, and has grooves in its foot so it can fit into another shoe bracket. This lets you slide the receiver into an umbrella mounting bracket designed to accommodate a hotshoe flash.

I’m not particularly impressed with the bracket design, since the size and length of the receiver mean that flash units attached to it are sort of sticking out on a not entirely sturdy plastic box in a somewhat vulnerable fashion. And the L bracket really isn’t strong enough to support the weight of a flash unit when used at any angle other than straight up and down. It’s actually a very flimsy design, in fact.

Aside from the on switch (which puts the unit into listening mode) the receiver has a red LED which illuminates when it receives a radio signal, a DIP switch block for setting the radio codes and a PC socket for hooking the receiver up to an external flash unit with no shoe. The receiver is powered by a CR2 lithium (not alkaline, as is sometimes incorrectly advertised) cell of the type used in some later-model Canon consumer film cameras. The battery may be wrapped in plastic, so if your receiver doesn’t work, double-check that. The DIP switch block is concealed inside the unit, and is accessed by opening the battery door.

The receiver is apparently designed to work with a sync (trigger) voltage of 6 volts or less, much like Canon EOS cameras. Any higher trigger voltage on the part of the flash unit (such as some AC-powered studio flash units, and a few older battery-powered flash units) may destroy the receiver.

Wireless range and reliability

I haven’t tested the transmitter/receiver pair fully, but it seems not to have the greatest range in the universe. I tested it indoors with no obstacles and it responded reliably up until about 10 metres or so. Not great, and certainly nothing compared to the range afforded by a PocketWizard or whatever, but for something this small and cheap that’s not surprising. Still, the eBay seller advertised a range of 30 metres, so it seems a bit on the low side.

I’ve also set up three receivers and fired them repeatedly to test, and they were not 100% reliable by any stretch. Somestimes they were just 60% reliable. The angle of the transmitter also made a huge difference - turning the transmitter just a bit would cause one of the transmitters to stop responding completely. This from a distance of maybe 3 metres. Very frustrating. Ah, well. The old adage about getting what you pay for does come to mind.

No automated flash metering

Automated flash metering is not possible with this setup. There is no way, for example, for Canon’s E-TTL automatic flash metering to work with this type of gear. This product is a simple flash trigger that fires the output of the flash units upon command of the camera. (ie: in sync with the opening of the camera’s shutter) There is no control over brightness or duration. It’s up to you to set the output levels of each flash unit to ensure your scene is correctly lit.

There are two ways to deal with this. The first is to use a flash unit with "autoflash" capabilities. Such flash units contain internal meters which can be set to match the shooting characteristics of the camera you’re using. The second is to set the output of each flash by hand and confirm the results, either through using a handheld flash meter or by examining the output on-screen if you’re using a digital camera.

It’s this latter which is becoming the most common mode of operation for this type of flash. You set the flash units in position, experiment with different output settings for each unit, and see what the result is. With time you’ll get used to appropriate settings for differing lighting conditions and won’t have to rely as much on the camera’s output. Until then you’ll probably spend a fair bit of time firing test shots and scrutinizing the histogram on your digital camera’s back.

For more information and incredibly helpful tips for using this sort of off-camera portable flash with manual metering, I definitely recommend David Hobby’s Strobist blog. It’s packed with a wealth of knowledge on how to do off-camera flash, particularly on a modest budget. Flash triggers like this can be an essential tool for a strobist fan operating with limited funds.

Compatibility issues

The version I have is described by the seller as a "V2" version, which is billed as resolving issues that the previous version of the product had with certain Canon Speedlite flash units. The symptom is the same problem you see when using such Speedlites with simple optical triggers - the flash will fire once at full power and then lock up and stop responding. You have to turn the flash off and on again before it’ll respond any further.

The V2 triggers are said to work with the 430EX and 550EX flash units. I can’t verify that at present, but the unit I tested seems to work fine with the Canon 420EX and 430EZ flash units, whereas ordinary optical triggers don’t. I also tried it with a cheapie old Vivitar flash without problems. I’ve heard from other users that their V2 triggers cause some Canon EX units to fire repeatedly, but I personally haven’t experienced that issue. Also, the V2 triggers apparently operate on a different frequency from their predecessors, so be aware of that if you own the earlier model. Finally, according to the eBay seller the triggers don’t work with Sigma EF-500 DG ST flash units or Olympus FL-36 flash units.


These products are, well, quite cheap. It seems they use the same basic technology as the wireless camera remotes I review elsewhere on this site. (ie: garage door opener type technology) They’re not particularly sturdily made - the plastic moulding is somewhat rough, the receiver bracket is extremely flimsy, and the electronics are quite crude, featuring uninsulated wires which cross over each other. And they do not trigger reliably each and every time. But for the affordable price that isn’t surprising. Though I do feel rather bad about the workers who have to solder these tiny things together by hand.

They aren’t super reliable, and don’t always trigger when you want them to, but if you need that kind of sturdy reliability then you need to invest in a pair of Pocket Wizard, Bowens Pulsar or Elinchrom Skysport radio triggers. And those professional-level products are prohibitively expensive for a lot of amateur photographers. The same goes for Canon’s wireless E-TTL system which works reasonably well and automatically, but is similarly expensive and also badly crippled by its reliance on line of sight infrared and visible light transmissions. So, if you just need something for the occasional hobbyist use, then these Cactus things are great.