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DPG would like to thank Kraken Sports for supplying a pair of KR-S40 strobes for the purposes of this review.
 

Sometimes a polkadot batfish just needs to focus! Dual snoots and a healthy dose of patience were required to fine-tune the lighting and wait for the batfish’s lure to be extended. The aiming lights on the KR-S40 are a tad underpowered in bright conditions but work well in the dark (Sony a1, Canon EF 50mm f/2.5 macro lens, Isotta housing, dual Kraken KR-S40 strobes with Backscatter OS-1, f/13, 1/320s, ISO 100)
 

At a time when strobe manufacturers are going bigger, badder, and more powerful—pushing flashgun designs to their limits—Kraken Sports has taken a refreshing step in the opposite direction. With the release of the KR-S40, they’ve introduced a compact, macro-focused strobe that feels like a throwback to the minimalist underwater lighting tools of the past. Aside from the hugely popular Backscatter Mini Flash 2 strobes, there haven’t been many recent contenders in the small strobe space. The KR-S40 reminds me not only of the Mini Flash, but also of the Inon S-series strobes—tiny, but well-suited for macro and close-focus wide-angle (CFWA) underwater photography.

Over the past several months, I’ve had a great experience using the KR-S40 here in Florida, especially at the macro hotspot that is the Blue Heron Bridge. It’s a near-perfect strobe for this environment—especially when paired with snoots. Kraken has a dedicated snoot for the KR-S40 but it was not available in time for this review, so I used the Backscatter OS-1 snoot (which is only designed to work with the MF-1 and MF-2). Yup, it fits snugly onto the strobe head and worked very well. If you already own accessories like snoots or color filters from other compact strobes, that compatibility makes the KR-S40 an even more attractive option.
 

A black striated frogfish looming out of the darkness. The KR-S40 is a great macro strobe, thanks to its small size and compatibility with a snoot like the Backscatter OS-1 or the dedicated KR-S40 snoot (Sony a1, Sony FE 28–60mm f/4–5.6, Isotta housing, Kraken Sports +6 diopter, single Kraken Sports KR-S40 strobe with Backscatter OS-1 snoots, f/13, 1/250s, ISO 100)

A Simple, Straightforward Design

I appreciate simplicity in gear—products that do what they’re supposed to do, without unnecessary frills. The KR-S40 embodies this philosophy. Its design is minimal yet functional, with an aluminum body housing and a straight flash tube. The controls consist of a power button, a fiber-optic port, a remote port, and a single large dial for adjusting power levels. That’s it. No confusing menus or hidden features.
 

Dual Kraken Sports KR-S40 strobes with flat diffusers attached to a Marelux Z6II housing with a Nauticam WWL-C and a Kraken Sports 7-inch monitor. The strobes are roughly the size of a small Coca-Cola can!
 

A small octopus perched at the mouth of the tin can it calls home. The color temperature of the KR-S40 is quite cool. Fortunately, there are warming diffusers nearly-to-market as at the time of this writing, but I did not have access to them for the review (Sony a1, Canon EF 50mm f/2.5 macro lens, Isotta housing, dual Kraken Sports KR-S40 strobes, f/5.6, 1/160s, ISO 100)
 

The KR-S40 also includes both white and red constant lights, which are incredibly useful for aiming snoots, focusing on shy subjects, or simply navigating in low-light situations if your dive light goes missing or dies. Conveniently, the light turns off when the strobe fires, so it won’t accidentally end up in your image.

Another feature worth highlighting is the remote port. If you’ve used Kraken’s larger strobes or their higher-end video lights, you may already be familiar with the RC02 remote. It allows you to control up to two KR-S40 strobes via a fiber-optic connection, adjusting power levels from a single control unit—a neat feature for streamlining your setup and speeding up your workflow.
 

A large lined seahorse, posing nicely for the Kraken KR-S40 strobes. I’m eagerly awaiting the arrival of the warming diffusers for these little flashes (Sony a1, Canon EF 50mm f/2.5 macro lens, Isotta housing, dual Kraken Sports KR-S40 strobes, f/3.2, 1/320, ISO 100)

Power and Triggering

Those familiar with Kraken’s naming scheme may know that the “40” in the KR-S40’s name refers to its maximum output in watt-seconds. While the KR-S40 isn’t going to blow your socks off with raw output, 40Ws at full power is respectable. If your primary subjects are sharks or large reef scenes, you’ll want to look at a flashgun with more power. That said, it is very much a macro-oriented strobe, and it shines in that role.

Available power settings are 40Ws, 20Ws, 10Ws, 5Ws, and 2Ws. I would’ve liked intermediate steps between 40–20 and 20–10, as the jumps can feel abrupt. I found myself mostly shooting at 10 or 20, occasionally dropping down or going full power depending on the situation.

The strobe runs on a single high-capacity 21700 rechargeable battery and is triggered via fiber-optic cable. Like other Kraken strobes, the KR-S40 is strictly manual—there’s no TTL functionality. While that may be a limitation for some, manual shooters will appreciate the direct control and predictability it offers.
 

A whip eel, an uncommon subject and one that is often quite hard to shoot as they are skittish, lit by dual KR-S40 strobes with Backscatter OS-1 snoots. The small size of the strobes, with or without the snoots, makes maneuvering them into position a breeze, especially for backlight or rimlight situations (Sony a1, Sigma 105mm f/2.8 DG DN Art macro lens, Isotta housing, dual Kraken Sports KR-S40 strobes with Backscatter OS-1 snoots, f/13, 1/320s, ISO 100)

Light Quality

Compared to its bigger siblings—the KR-S80 and KR-S160, which both feature circular flash tubes and produce beautifully soft, even light—the KR-S40’s rectangular flash tube creates a noticeably harsher beam. This might not appeal to everyone, but I’ve come to appreciate it. I love contrast and texture in my macro shots, and the not-so-soft beam of the KR-S40 makes it easier to bring out those elements, especially when working with textured subjects or dramatic lighting setups.
 

An orangespotted goby perched at the entrance to its burrow. While the light quality from the KR-S40 isn't world-beating, it is certainly possible to get nice, soft light out of these strobes even at wide apertures when it can be easy to blow out your image (Sony a1, Canon EF 50mm f/2.5 macro lens, Isotta housing, dual Kraken Sports KR-S40 strobes, f/3.2, 1/320s, ISO 100)
 

The cool color temperature of the KR-S40 may not be appealing to some, as it can turn images rather blue. However, in certain situations, I don’t mind the cooler color, but it did mean I had to warm up this octopus in post, for example. I feel it constrasts well against the bluer surroundings (Sony a1, Canon EF 50mm f/2.5 macro lens, Isotta housing, dual Kraken KR-S40 strobes, f/4, 1/250s, ISO 100)
 

Using a diffuser definitely softens the light and is recommended for general macro use, but I personally enjoy the crispness of undiffused light when I want to emphasize details and textures, especially for macro work.

As already mentioned, Kraken does offer a dedicated snoot for the KR-S40. During my testing, I didn’t have access to it, but the Backscatter OS-1 snoot—originally designed for the Mini Flash—fits the KR-S40 head snugly and functions beautifully. That compatibility was a pleasant surprise, and I was able to produce images I’m genuinely pleased with using that setup.
 

A common octopus featuring all the textures. Harsh light is fantastic for bringing out textures and contrast on subjects, especially when using cross-lighting and snoots (Sony a1, Canon EF 50mm f/2.5 macro lens, Isotta housing, dual Kraken Sports KR-S40 strobes with Backscatter OS-1 snoots, f/10, 1/30s, ISO 100)

Final Thoughts

The Kraken Sports KR-S40 is not a strobe for everyone—but for the macro shooter, it’s a lightweight, reliable, and surprisingly versatile lighting tool. Its small footprint, straightforward design, and compatibility with existing snoots and accessories make it a worthy addition to any macro photographer’s kit. While the light is a bit harsh without modifiers and the power steps could be a bit finer, these are minor trade-offs for a strobe that does its job and does it well.

A male banded jawfish aerating its eggs. The KR-S40 makes for a formidable macro tool! (Sony a1, Canon EF 50mm f/2.5 macro lens, Isotta housing, dual Kraken Sports KR-S40 strobes with Backscatter OS-1 snoots, f/13, 1/320s, ISO 100)
 

About the Reviewer: Matthew Sullivan is a Florida-based wildlife photographer who has been diving since he was 10 years old. He has traveled extensively, visiting well-known dive destinations such as Guadalupe Island, Indonesia and the Philippines, but he also likes to dive closer to home in Florida. When not taking pictures underwater, he can be found trekking mountains, or exploring national parks and rainforests in search of new adventures and wildlife encounters.
 

Kraken Sports KR-S40 Strobe

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