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The author would like to thank AOI for providing a pair of their Ultra InTeLi P1 (UIS-P1) strobes with a set of white wide-angle diffusers.
 

In an underwater gear landscape where it seems every company and their mothers are producing new strobes, Hong Kong company AOI has joined the fray. AOI is not a newcomer to high-quality underwater products: Not only do they produce a fantastic line of housings and accessories and create a number of products for other companies, but they have now cannonballed into the high-end strobe market.

I recently received a pair of these new strobes, the wonderfully named Ultra InTeLi Performance 1—or UIS-P1 for short. After several years of using AOI’s entry-level Q1 RC strobe, I was beyond excited to be the first person to take these impressive—and much anticipated—beasts underwater!
 

The AOI UIS-P1 flashgun has become my go-to light source for my underwater photography. The strobe features plenty of power and fantastic light quality (OM System OM-1, Olympus 8–25mm f/4 Pro, AOI UH-OM1 housing, dual AOI UIS-P1 strobes, f/8, 1/40s, ISO 400)
 

AOI’s UIS-P1 strobes were first introduced at DEMA 2024 and promised advanced performance, intuitive usability, and cutting-edge technology. For several months, I have had the pleasure of letting the UIS-P1 rip in the colorful, warm waters around Grand Cayman. I got a real feel for the features, ergonomics, and overall performance of this new flashgun.

Note that the images accompanying this review are straight out of the camera. I have made no adjustments to the color temperature of the light. The only adjustments performed were minor contrast tweaks and minor backscatter removal.
 

A sharknose goby perched on a coral head: The beautiful soft light from the AOI UIS-P1 allowed me to show off every little detail and all the gorgeous colors on this wonderful little fish (OM System OM-1, OM System 90mm f/2.8 Macro, AOI UH-OM1 housing, dual AOI UIS-P1 strobes, f/8, 1/250s, ISO 200)
 

An adorable smooth trunkfish showing its best side: Soft, even lighting is wonderful for portraits of reef fish (OM System OM-1, Olympus 8–25mm f/4 Pro, AOI UH-OM1 housing, dual AOI UIS-P1 strobes, f/8, 1/250s, ISO 200)

The UIS-P1 strobes are massive compared to my much-loved Q1 RC. That larger size and heft are a result of higher build quality and the serious power on board, though the increase in size allows for a less cramped design.

As often seems to be the trend these days, the UIS-P1 features a marine-grade aluminum body and a circular flash tube. Powered by dual 21700 batteries, the UIS-P1 produces 150 watt-seconds of power and is rated at 540 shots per charge at full power. I am quite fond of the smart battery indicator, as it communicates the remaining battery life and number of flashes, which provides the direct feedback I need to decide whether to charge the batteries or not for the next dive.

Of course, as with any strobe, power specs have to be taken with a grain of salt, as every manufacturer measures these things slightly differently. I can confidently say, however, that the UIS-P1 far surpasses the Q1 RC in terms of power, and I did not encounter any scenarios where I was left wanting for more. More on power and light quality later.
 

UIS-P1 Specifications

• Maximum power: 150Ws
• Beam angle (with diffusers): 150°
• Color temperature: 5900K
• Recycle time (full power): 1.8 seconds
• Flashes per charge (full power): 540
• LED light: 3,000 lumens
• Battery: 2x 21700
• Depth rating: 330 feet (100 meters)
• Dimensions (L x W x H): 8.1" x 3.6" x 5.3" (205mm x 91mm x 133.5mm)
• Weight (with battery): 41.6oz (1,180g) in air; 8.1oz (230g) underwater

Clockwise from top left: The circular flash tube in all its glory; easy to use controls and a handy display; the OM System OM-1 test rig; diffuser and light modifiers
 

Despite the impressive specs, the UIS-P1 is a relatively simply designed flashgun. It sports a rounded power knob on the rear of the body, right next to a small LCD screen that indicates mode and power settings. The only other two controls are a test button and the power-on/focus light button. A standard 1-inch ball mount is included.

Happily, AOI had some light modifiers ready to go for my review. Often we have to wait for accessories to come out well after the strobe has been released, but fortunately, no such wait was necessary this time. I loved the white dome diffuser, which did a wonderful job of even further softening the beam from the UIS-P1. The accessories I was most excited about were two that weren't available for the Q1 RC. AOI has introduced a silver reflector to narrow and boost the light from the flash, alongside a beam restrictor to cut down on the light spread for a more focused beam.
 

A green moray hidden beneath an overhanging outcrop: Notice the soft shadows around the eel, characteristic of a wide, soft, even flash beam (OM System OM-1, Olympus 8–25mm f/4 Pro, AOI UH-OM1 housing, dual AOI UIS-P1 strobes, f/8, 1/60s, ISO 200)
 

A spotted scorpionfish, masterfully camouflaged against the its rocky surroundings: Shooting with the diffusers on the UIS-P1 allows for an interesting natural history image but the scorpionfish can be quite difficult to see, especially if you aren’t familiar with them (OM System OM-1, Olympus 8mm f/1.8 Pro Fisheye, AOI UH-OM1 housing, dual AOI UIS-P1 strobes, f/8, 1/250s, ISO 200)
 

A different spotted scorpionfish, photographed with the UIS-P1 beam restrictor and all of a sudden the image is filled with interesting textures and shadows and the fish itself pops right out of its surroundings (OM System OM-1, Olympus 8mm f/1.8 Pro Fisheye, AOI UH-OM1 housing, dual AOI UIS-P1 strobes, f/8, 1/250s, ISO 200)

When AOI released their first strobe, the ultra-compact Q1 RC strobe, they introduced one of the most reliable TTL modes for underwater photography in the RC-TTL and i-Macro (TTL for macro) for Olympus/OM System shooters. These TTL modes are calculated to manufacturer’s specifications and provide consistent and accurate exposures, and I have long enjoyed the results my Q1 RC’s provided.

The new UIS-P1 strobe introduces the next generation of this intelligent TTL by providing support for Sony shooters as well, allowing them to take full advantage of TTL, i-Macro, and both HSS and M-HSS functionalities—a game-changer for anyone capturing fast-moving subjects. The UIS-P1 strobe also allows for full manual control of the flash output with 10 different settings that offer half-stop adjustments to the light output, putting full creative control into the hands of the photographer. I could control the output easily with the power dial, and the LED display on the back showed me exactly how much power was left at each setting.

A standout feature for me, using the UIS-P1 with my Olympus/OM System cameras, was the RC-TTL’s ability to adjust to varying lighting conditions, especially in high-contrast scenarios like backlighting.
 

A small group of schoolmaster snapper hang near a gorgonian: Schoolmasters can be very, very reflective, but the quality of the light from the UIS-P1 and its accurate TTL capabilities ensure properly exposed subjects (OM System OM-1, Olympus 8–25mm f/4 Pro, AOI UH-OM1 housing, dual AOI UIS-P1 strobes, f/8, 1/60s, ISO 200)
 

A small harlequin bass, a ubiquitous presence on Grand Cayman’s reefs: The OM-1 autofocus has no issues keeping up with this fish as it flits about, and the TTL compatibility between the camera and the UIS-P1 ensures natural-looking lighting on each portrait (OM System OM-1, Olympus 60mm f/2.8 Macro, AOI UH-OM1 housing, dual AOI UIS-P1 strobes, f/4, 1/250s, ISO 200)

No matter how well designed, well built or feature-packed a strobe is, the quality of light produced by the flash remains the most important factor, as this is what impacts the final image more than anything else. The circular flash tube on the UIS-P1 already arguably gives it an edge over strobes with straight flash tubes, as circular flash tubes tend to produce a wider, softer beam.

While it is a relatively cool color temperature of 5900K, the light from the UIS-P1 is wonderfully soft and even. Of course, strobe positioning and basic understanding of lighting are significant factors, but if you get those down, the UIS-P1 will reward you with fantastic light quality. The beam angle is rated at 100 degrees with no diffuser, but the white wide-angle diffuser widens and softens the beam very effectively.
 

A photogenic porcupinefish hams it up for the camera. Soft, natural looking lighting is the name of the game for the UIS-P1, especially with diffusers (OM System OM-1, Olympus 8–25mm f/4 Pro, AOI UH-OM1 housing, dual AOI UIS-P1 strobes, f/8, 1/160s, ISO 200)
 

An often overlooked benefit of a high power strobe is the ability to shoot at lower powers. Sounds paradoxical, right? However, the higher a strobe’s maximum power, the greater your ability to shoot with a lot of light without maxing out the strobe. The lesser the percentage of the maximum power you are using, the nicer the light quality will be. For example, a strobe rated at 150 watt-seconds shooting at 80 watt-seconds—roughly half power—will produce better looking light than a full dump from a strobe with an 80 watt-second rating. Suffice it to say, even in bright Caribbean water, I had absolutely no issues lighting big animals or big scenes.
 

The UIS-P1 strobes handled wide-angle scenes like this cluster of yellow tube sponges without issues. The combination of high power and a wide beam, especially with the wide-angle diffusers, meant that I could easily light this whole outcrop (OM System OM-1, Olympus 8–25mm f/4 Pro, AOI UH-OM1 housing, dual AOI UIS-P1 strobes, f/8, 1/60s, ISO 200)
 

A common octopus moving over a shallow, storm battered reef: Many of these shallow Caribbean reefs suffer from bleaching events, being “loved to death” and storms. Despite that, this octopus and some sentinel sea fans made for a nice scene, easily and beautifully lit by the UIS-P1—no hotspots, no shadowed areas, plenty of color and detail (OM System OM-1, Olympus 8mm f/1.8 Pro Fisheye, AOI UH-OM1 housing, dual AOI UIS-P1 strobes, f/8, 1/200s, ISO 200)
 

A delicate little shrimp, hiding in the crevices of a sponge: Often, lighting like this can be difficult as the sponges are closer to the light source than the shrimp, but a forgiving beam meant that everything was nicely lit (OM System OM-1, Olympus 60mm f/2.8 Macro, AOI UH-OM1 housing, dual AOI UIS-P1 strobes, f/6, 1/250s, ISO 200)

One of the best pieces of advice I received when I began my underwater photography journey was to invest in a great pair of strobes, as a quality set will often last a photographer through several camera system upgrades. Conversely, if photographers skimp on their first set of strobes, they may quickly outgrow them and end up purchasing a better set, which can ultimately cost more than if they had invested in quality flashguns from the start. So, while the UIS-P1 is double the price of AOI’s entry-level Q1 RC—$899 at the time of writing—it falls squarely into the category of quality strobes that will last through multiple system changes. It’s also an investment that is comparable to other midrange strobes on the market.

The UIS-P1 offers the user a compelling combination of power, speed, and advanced technology for serious underwater photography. The user-friendly controls and excellent light output make these strobes a fantastic choice for both macro and wide-angle shooting. While the strobe market is now awash with high-quality strobes, if you are looking to take your lighting setup to the next level—or indeed invest in great strobes from the outset—the UIS-P1’s impressive performance and extensive feature set mean AOI’s new flagship strobe certainly warrants consideration.
 

One of my favorite subjects is this small green turtle, reliably found at a local seagrass bed. She came up to me to oggle the UIS-P1s! (OM System OM-1, Olympus 8mm f/1.8 Pro Fisheye, AOI UH-OM1 housing, dual AOI UIS-P1 strobes, f/8, 1/250s, ISO 200)
 

Gorgeous coral details, constructed like some sort of maze: Whether shooting macro or wide angle, the AOI UIS-P1 is capable of handling any situation (OM System OM-1, OM System 90mm f/2.8 Macro, AOI UH-OM1 housing, dual AOI UIS-P1 strobes, f/11, 1/200s, ISO 200)
 

About the Reviewer: Andrew McLachlan is a full-time freelance photographer/writer originally from Ontario, Canada. For as long as he can recall, he has been fascinated by the natural world. Andrew’s photography became an extension of that love, and if he did not own a camera, he would still be found outdoors observing all that nature has to offer. During Andrew’s time in Ontario, he built a large, diverse collection of images featuring landscapes and the flora and fauna from the province. For the past two years, Andrew has resided on Grand Cayman in the Cayman Islands. Andrew uses an OM System OM-1 and M. Zuiko lenses, AOI housings, lens ports, and strobes for all of his work beneath the waves. Andrew pursues his underwater photography through both snorkeling and scuba diving and finds each to be equally rewarding in terms of subject matter. Knowing where to look and what signs to be aware of will often yield incredible photo opportunities in shallow ocean settings.
 

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AOI UIS-P1	OM System OM-1 Mark II		AOI UH-OM1 for OM-1 I & II