High Speed Strobe Test: The Profoto Acute 2R 1200
While perusing the stats, photos from a number of my test shoots, and thinking through my review of the little Profoto pack sitting on my desk, I kept coming back to one number, “.09″. It’s the number of seconds Profoto claims it takes the Acute 2R 1200 to recycle at minimum power. That’s better than ten frames per second, better than 10 Hz from a strobe pack under $2,000 and smaller than a Mamiya RZ.
I wanted to set up an informal studio set to test the claim. I thought of dancers, martial artists, tennis players drilling dusty yellow balls at 10 FPS… settled on a still life that would really show variations in light intensity and color. These tests, of course, are always dubious, too many variables to list, but the experience was awesome. In short, I was able to generate usably consistent images at Eleven Frames Per Second, from this cute black box, and it was easy.
Given the informality and range of possible variables, please consider this an interesting observation and not an in-depth test. Also, feel free to join the discussion on our new Facebook page.
I used a Nikon D3 with 60mm f2.8D macro lens. Between its customizable low and high speed continuous shooting settings, the D3 allows a range from 3 FPS to 11 FPS in 1 FPS increments. I chose 1/250 as my shutter speed to best emulate what I think would be most likely in a “real world” version of this shoot, which is to say whatever settings would minimize ambient light to make the most of the somewhat casual 37.5 W/s (the pack’s lowest and fastest setting). I chose ISO 200 and f5.0, allowing a proper exposure based on the observed exposure once the pack had dumped its initial full power pop (which overexposed everything slower than seven frames per second, as the pack actually had time for a complete recycle).
Digital capture was compressed “medium” size JPGs with no post production except resizing and watermarking. The results are, therefore, as close to straight out of camera as the practice of Web publishing will allow.
The Acute 2R 1200 was dialed to its lowest setting, meaning its 2-stop dimmer was at -2, and both channels were at 1/4 power. I used two heads, one in B channel and one in A, finding no discernible difference between one or two heads or between combined or asymmetric power distribution. One head had a 2.3 foot Octa soft box mounted, one had the standard Profoto zoom collar reflector. The pack was running of a 110V AC power source, modeling bulbs were not used, though they appear to have no effect on strobe recycling speed.
To begin, I did push slightly past the Acute 2R 1200′s limitations and perhaps illustrate an advantage of higher priced Profoto packs (I look forward to repeating this test with a Profoto D4 and Pro-8). That limitation is this: the Acute 2R 1200 does not completely recharge after the first frame at seven frames per second or faster. Seven frames per second is somewhere near half the Acute 2R 1200′s advertised .09 second recharge time. Possible explanations? Perhaps the advertised rate is based on 220V and not 110V, or perhaps, as is common for lighting statistics, the number is based on something besides 100% power.
Whatever the explanation, I was not disappointed, because, despite not reaching 100% power, the pack settled into a very consistent power level after the initial frame. The consistency continued practically without limit (the camera’s buffer filled before the flash slowed at every available speed, shooting JPG, none the less). If photographers plan for an exposure based on frame 2, 3 4, etc.. and not 1, they will not be disappointed with the Acute’s rapid fire abilities. Also, I found no difference in consistency between nine frames per second, 10 frames per second, even the D3′s top setting of 11 frames per second. Comparing frame #10 from each series reveals remarkably consistent color and exposure, amazing at such speed and for an entry-level compact pack.
Profoto packs, including the Acute 2, are wired with safety systems that prevent overheating. In the past, I’ve had Profoto packs slow down for cooling (including one memorable experience with a smoking Pro-7 rental that took an hour to start firing again). During testing, including weeks of ambitious shooting, our Acute 2R 1200 never blinked. As you’ll see below, I observed only one underexposed frame in my ten frames per second series (frame #7). It was likely a one time slip that would have been fixed with a re-shoot of the set, but was worth keeping for the sake of journalism.
My summary, based on this quick test, a range of experience with strobes from various manufacturers, and several weeks of aggressive shooting with the Acute 2R is that the pack is highly capable, deceptively simple, and rugged enough to take a full portfolio of abuses. I’m really impressed with its speed, which has obvious “real world” creative application. There is observable room for improvement at these ridiculous extremes, not to mention that speed is greatly reduced at full power. The Acute 2R, though, is the high-speed champ in its class and the title is well deserved.
A Brief Aside on Flash Duration
The opening image is a series of photos captured to experiment with the Acute 2R 1200′s motion stopping speed. Profoto claims 1/3200 s, which is impressive. The above two frames (which can be enlarged in a new window with a click) show that the pack has a limit to its motion freezing abilities. The toy dolphin is falling from about two feet and already moving too quickly to be un-blurred. Also, the relatively static water is sharp while quickly moving droplets are also blurred.
This is certainly not a conclusive test, just another observation, though perhaps one that suggests we’re seeing somewhat less than 1/3200 s. Typical of marketing materials for strobes, Profoto’s listed 1/3200 s duration is listed as “t 0.5″, meaning that half the pack’s power is released in 1/3200 s. One popular rule of thumb converts t 0.5 to t 0.1 (time for 90% of flash output) by dividing the t 0.5 number by three. The result of that places the pack closer to 1/1000 s, which also seems closer to consistent with my observations.
Using very high ISO and a 1/4000 s exposure (without strobes) I was able to more completely freeze the falling dolphin and flying drops. Again, the Profoto posts a respectable performance, unlikely to be decisively beaten by anything at the same or lower price, but leaves the world class performance to its big brothers. The stats improve (especially flash duration) with each step from Acute to Profoto D4, from D4 to Profoto Pro-7*, and from Pro-7 to Profoto Pro-8.
*As an older design, the Pro-7 is difficult to fit in the lineup, the D4 is actually listed as faster, in terms of recycle time.
Notes on Images
The opening image is a montage of several photos as discussed in the previous section. The sections below are series of images shot in one burst. In every case, the images indicate the first “take” and the pack and heads were allowed to cool for about three minutes between takes.
3 Frames Per Second
4 Frames Per Second
5 Frames Per Second
6 Frames Per Second
7 Frames Per Second
8 Frames Per Second
9 Frames Per Second
10 Frames Per Second
11 Frames Per Second
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