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PocketWizard AC7 shield tackles RF noise problem with certain Canon Speedlites  
Tuesday, May 26, 2009 | by Rob Galbraith
LPA Design's upcoming PocketWizard AC7, a shield designed to squelch range-limiting RF noise emitted by certain Canon Speedlites, is nearing completion. In our testing of an early prototype with a Speedlite 580EX, MiniTT1-to-FlexTT5 wireless radio triggering range was almost four times longer than the same setup without the AC7 in place (and LPA Design indicates that shipping units will provide even greater RF noise suppression - and therefore longer range - than the one supplied to us).

Squelch: A prototype PocketWizard AC7 RF noise shield, with a Canon Speedlite 580EX inside and a FlexTT5 attached. Click to enlarge (Photo by Rob Galbraith/Little Guy Media)

First and foremost, the PocketWizard AC7 is meant to keep Canon Speedlite RF noise away from a PocketWizard FlexTT5 receiver, noise that interferes with its ability to receive an incoming radio trigger signal.

RF noise emanates out from the Speedlite body, and it also passes down through the flash's foot, so the AC7 provides shielding for both. It's a three-sided, 8in (20cm) x 4.5in (11cm) x 2.5in (6cm) plastic shell, with a combination hot shoe and foot in its base. The shell incorporates RF shielding, as does the shoe/foot piece. The Speedlite slips inside the AC7 and attaches to its shoe. Together, they're attached to a FlexTT5, and then mounted on a light stand via its foot or 1/4-20, or one of two 1/4-20 mounts built into the bottom side of the AC7. The back of the AC7 is open - that is, it has no back - and provides full access to the flash's LCD panel and controls.

Because the prototype we have is not quite final, we've opted to do only limited range testing for now. We've experimented enough, however, for it to become apparent the AC7 will be a viable solution to the RF noise problem that has frustrated some owners of the 580EX and 580EX II. A solution that should allow these Speedlites to be used with the positioning flexibility and long working distances previously possible with the new PocketWizards only if the Speedlite was a 550EX, 430EX II or other Canon flash that emits little or no RF noise across U.S./Canada PocketWizard frequencies.

Here's an example of the range improvement: in a typical outdoor portrait setup using a small umbrella, the maximum reliable ControlTL trigger distance we're able to achieve from a MiniTT1 transmitter to a 580EX mounted on a FlexTT5 receiver is about 100ft (30m). With the same flash inside the AC7, the maximum range increases to about 380ft (116m).

The photos below illustrate the distance difference. The first is shot at the maximum distance possible without any RF shielding, the second with the AC7 in place. Both photos have been captured with a 50mm lens on a full frame digital SLR, which means they roughly approximate a normal perspective, without any exaggeration or compression of distance. The round bright spot in each frame is, of course, the 580EX lighting up an umbrella.

Short Game: The MiniTT1-to-FlexTT5 working distance with no RF shielding around the Speedlite 580EX. Click to enlarge (Photo by Rob Galbraith/Little Guy Media)
Long Drive: The MiniTT1-to-FlexTT5 working distance with the Speedlite 580EX inside a prototype PocketWizard AC7 RF noise shield. Click to enlarge (Photo by Rob Galbraith/Little Guy Media)

The final production version of the AC7 is to have incrementally better RF noise shielding than the tested prototype, says LPA Design's Jim Clark. How much better is difficult to quantify precisely, he says, but it could translate into perhaps a 20% bump in working distance compared to our prototype AC7. (Officially, the company is promising a total range increase of 300-500%.)

Prior to the arrival of the AC7, we'd been using a fabric wrap made from a material called VeilShield. As we've written previously, it works well, but it's no match for LPA Design's upcoming product. In the same distance test as described above, wrapping the 580EX in the VeilShield material allows a working range of 220ft (67m), which is quite good but well short of the 380ft (116m) of the prototype AC7. The aerial photo below depicts the working distances we've achieved between a MiniTT1 transmitter and FlexTT5 receiver, with and without RF shielding of some kind.


Incidentally, we also tried a 430EX II - which is not an RF noisy Speedlite - and its maximum reliable ControlTL range is about 350ft (107m) in the same test without any RF shielding. We've had zero problems with or concerns about the 430EX II's usable range with the MiniTT1 and FlexTT5, it has been our go-to remote flash alongside the older 550EX, so the fact that the prototype AC7 allows for a range that slightly exceeds this with the 580EX is a promising sign.

For those who want a geekier take on the effectiveness of the AC7, below are 20-second screen movies of an RF noise meter feature in software used internally at LPA Design. We employed the software to check RF noise levels with a 580EX and 580EX II, with and without the AC7. In each movie below, the Speedlite is turned on almost immediately after the video starts, and then the noise meter displays, in feet, the unit's wireless range in open space. This should be a solid indicator of the maximum possible working range when there are no obstacles or RF absorbers nearby.

The green bar represents the distance range at which triggering reliability is assured. Once the distance range marked in yellow is reached, triggering reliability is reduced. Red means triggering success is unlikely.

Tip: If you start all four movies in rapid succession by clicking each play triangle, you'll be able to easily compare the overall RF noisiness of each configuration. Note that the movie of the 580EX inside the AC7 may not look like its playing when it actually is, because the range bar stays at maximum through most of the 20-second clip.

Noise Meter: 580EX, no RF shielding
Noise Meter: 580EX inside a prototype PocketWizard AC7
Noise Meter: 580EX II, no RF shielding Noise Meter: 580EX II inside a prototype PocketWizard AC7

As you can see, our tester 580EX II is RF noisier than our tester 580EX. This fits with real world experience as well, though not to the extent shown by the noise meter. The 580EX II's unshielded range has definitely been shorter than the 580EX, but the difference hasn't been as significant as the meter suggests.

Also, LPA Design's own noise meter checking of a much larger sampling of 580-series Speedlites indicated that there is a noticeable unit-to-unit variation in RF noise at U.S./Canada PocketWizard frequencies, in both the 580EX and 580EX II models. The good news is that the AC7 should mostly level things out, such that regardless of how RF noisy your particular 580EX or 580EX II happens to be, you should still get a big improvement in range and positioning freedom.

The other benefit of the AC7 is a design that tilts the Speedlite on its side when mounted to a lightstand using one of the AC7's 1/4-20 sockets. This lowers its profile, which in turns means less blocking of returning light by the flash+AC7+FlexTT5 combo when illuminating a reflecting umbrella. And, the AC7 will also angle the flash so that it's pointing at the centre of the umbrella (when the umbrella shaft is attached to a typical lightstand accessory such as the Photoflex Shoe Mount Multiclamp pictured in several photos in this article). The main benefit of the AC7 will be its RF noise shielding, but better Speedlite positioning in umbrellas is going to be a nice bonus.

All PocketWizards sold in the U.S., Canada and a handful of other countries operate in the 340-354MHz frequency range. Three current and recent Speedlites emit RF noise in this same band: the 430EX, 580EX and 580EX II. The AC7 will accept any of these three, but is really designed with the latter two in mind.

Its length is the reason. LPA Design has made the AC7 just slightly shorter than the 580EX and 580EX II, to allow for the attachment of most light modifiers such as those in the HonlPhoto lineup that strap on with velcro. The smaller 430EX, however, doesn't peek out the end, and in fact stops well short, which means that attaching modifiers is trickier and its light won't fill out an umbrella on one side because the flash head is slightly blocked by the AC7.

This is with flash head pointed straight up and out the end of the AC7; with the head angled backwards both these problems disappear, but now the head of the flash is no longer shielded and sends gobs of range-reducing noise direct to the FlexTT5 receiver's antenna.

So, the 430EX can be used with the AC7, and it should provide a dramatic improvement in working range, but LPA Design really is targeting the 580EX and 580EX II in the product's overall design.

Side Show: A Speedlite 580EX II inside a prototype PocketWizard AC7 (Photo by David Schmidt/LPA Design)

The photo above shows the AC7 at this point in its development, but its appearance is to change by the time it hits the streets. The shell itself will still be the same overall size and shape, and it will remain open at the back, but an umbrella mount and pistol grip that are non-removable elements of prototype units will be eliminated (the company is planning instead to develop an optional pistol grip/umbrella mount accessory for the AC7).

Stripping away these elements from the product is just fine, as we were not impressed by either feature on the prototype. In fact, their elimination from the AC7 will only help trim down the amount of space it takes up in a camera bag (with the flash left inside it during transport, the AC7 shouldn't add too much carrying bulk). The final design, as shown in the computer-generated renderings below, has twin 1/4-20 sockets on one side plus, to make room for an external battery cable, a small protrusion on the other.

Mount Up: A computer-generated rendering of the final design of the PocketWizard AC7, showing the twin 1/4-20 mounts on the bottom side plus a cutout for access to the swivel release button on the flash head (Graphic courtesy LPA Design)
Profiled: A computer-generated rendering of the final design of the PocketWizard AC7, showing a bulge for the external battery cable on the top side (Graphic courtesy LPA Design)

While the best solution would be for the 580EX and 580EX II to just work without range limitations with the U.S./Canada FlexTT5 receiver, the AC7 is shaping up to be a usable workaround for owners of these Speedlites, one that gives the added benefit of better placement of the flash in an umbrella configuration. The 430EX will benefit too, but as noted earlier in the article, the 580EX and 580EX II are literally a better fit.

The PocketWizard AC7 is tentatively scheduled for release in July 2009, at a price that's promised to be affordable, though LPA Design hasn't finalized what that price will be.

The AC7 may not be the only RF noise-related product coming from LPA Design. A company press release announcing the AC7 hints there may be "other solutions to maximize the performance of the ControlTL system," though it does not provide any details about what those solutions might be.

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