Alex Mustard's Grand Cayman Gear Report: Sony A7RVI Battery Life, Fisheye Testing, and Hamlet Spawning

In this article from The Underwater Photography Show, we'll be diving into the gear from our 200th episode — Sony A7RVI battery life, a controversial fisheye lens test, and evening hamlet spawning dives in Grand Cayman.

This was my second trip with the Sony A7RVI, and it gave me the chance to properly conclude on the battery life underwater — something we didn't cover in our original review episode after the camera in the Red Sea. The A7RVI uses a new, slightly chunkier battery than previous Sony bodies, paired with power-saving features like an EVF that drops into a dark mode after a few seconds of inactivity. Together, these combine for an exciting big jump in real world battery performance.

For context: in the Red Sea, with a brand-new battery, I could do two short dives on the wreck of the Thistlegorm and still have 80% remaining — theoretically enough for ten dives on one charge. On a longer, 80-minute dive at Ras Mohammed shooting 250–300 images, the battery would drop to around 80% after just one dive. In Cayman, shooting three longer dives in a day, the battery comfortably lasted the full day — on one occasion sitting at 58% after three dives, a marked improvement over any other Sony body I've shot.

The battery is charged via USB-C and slots in easily to the new charger. The percentage readout is also better calibrated against real camera use, so the number shown is far more believable than on previous models. So far I have still been switching batteries at midday, really out of habit from having the A1.

By comparison, I (Matthew) have been shooting the Nikon Z9 for a couple of months, which has excellent battery life thanks to its larger body and battery — the A7RVI is getting closer to that kind of performance in a much smaller, lighter package. I'd expect this new battery design to become the standard across Sony's future bodies.

With rumours about a new Sony fisheye lens coming soon (EDIT — and now announced as the 8-14mm zoom), I thought it would be a good time to investigate their much-ignored current fisheye: the Sony fisheye adapter. The accessory lens is designed specifically to attach to their 28mm f/2 E-mount lens, turning it into a fisheye. The reason for testing the fisheye adapter now was practical. I'd been using an old Nikon 8-15mm fisheye on Sony via a Monster adapter for split-level photography, but that adapter has proven unreliable — it actually failed mid-trip in the Red Sea. The Sony adapter, at only a couple hundred dollars, offered a lighter, more reliable alternative, with the added benefit of an electronic connection that registers the fisheye in-camera (showing up as a 16mm focal length equivalent) and giving me a 28mm lens option on those trips.

Image quality-wise, the files are very good — nothing to complain about, but also not files that make you say "wow." I'd happily use it for professional work, though it isn't my frontline fisheye choice; I'd reserve it mainly for split-level shots or situations where a dome port helps a model see their own reflection. I still think a secondhand Canon 8-15mm on a Metabones adapter is optically superior, has that wow-factor, and is probably comparable in total cost. But the appeal of the Sony fisheye adapter is versatility: it travels as a 28mm prime with a fisheye option built in, and that 28mm gives me a backup in case my 28-60mm goes wrong, since I can still use my wide-angle wet optics (WACP/FCP) with the 28mm prime. For the Cayman trip, I shot the fisheye behind a 230mm dome with a 20mm port extension and conclude it is a decent solution, especially for those wanting a fisheye for specific shots, like split levels.

During the trip, I dropped my camera and broke the port shade on my Nikonos RS13, along with a Retra strobe — something that's surprised me given how many drops those strobes have survived over the years, though this one was a heavy impact onto metal. The cause was a change in routine: my wife wanted to swap strobe arms, so I gave her mine. And those strobe arms didn't accept my usual carrying clip, so in a hurry, I improvised with bungee cord instead. After a few days the bungee came undone, and that's how the camera fell.

For the rest of the trip I used two bungees on each side as a backup. The broader lesson is that these problems tend to arise when you're forced to deviate from your norm. Much of the reliability of my gear over the years comes from not changing things unnecessarily. A change opens you up to unexpected problems.

My D850 came out of retirement for Cayman. Although she could have shot the Sony A1, we always knew we'd be taking the D850 to Cayman for my wife, Eleo, to shoot topside. I only have one long Sony lens, and previously Eleo has been relying on a Nikon 500mm PF lens adapted onto the Sony body via the same unreliable adapter that failed with the fisheye lens. So once that broke, we knew we'd need a Nikon body for telephoto topside work. Eleonora had been shooting the D5 at home in the run-up to the trip and felt comfortable sticking with an SLR for UW, rather than switching to the Sony A1, which she'd not used underwater for a few years.

It was a nice reminder of how well set up my old Subal housing still is — it has an Underwater Light & Magic trigger for flash sync, a Nauticam vacuum system fitted by Aquaphot in the UK, Saga macro ports, and a Nauticam viewfinder adapter. The optical viewfinder does feel a bit dull after getting used to an EVF! Still, it was great to see my ol' buddy back in the water after so many good trips together.

Away from the workshop itself — which delivered the usual wide-angle staples of wrecks, models, stingrays, sharks, and turtles in beautifully warm water — I had a rare chance to photograph hamlet spawning. Normally when I run back-to-back workshops in Cayman, evenings are taken up with teaching, so I hadn't photographed the hamlets for about a decade. This time, with my parents looking after my daughter Isabella for an evening, my wife Eleo and our friend Liv and I went out to find the hamlets.

I timed the dive the old way — by the height of the sun above the horizon at the site — and despite running slightly late, we found the first pair spawning as soon as we got down. We saw both black hamlets and barred hamlets spawning that evening. I tried shooting on rapid fire with the Retra Maxis, but I don't think it added anything. With hamlets it is the pose of the adults, rather than the egg release that makes for a stand out image — which comes from camera angle, not moment. A lesson that new tech and high frame rates aren't always simply better for behaviour shots. I think if I had shot less and composed more, I would have got great images.

I also tried high speed shooting with a yellowhead jawfish spitting out his eggs, using a 100mm lens with a 2x teleconverter for reach, and the Retra Maxi strobes again. The A7RVI autofocus locked onto the eye so reliably that a traditionally difficult shot became easy. The high frame rate meant I got 10+ shots, where usually I'd get just one or two — but compositionally they weren't actually any improvement.

I also did some pike blenny-and-mirror photography, a classic technique for provoking a territorial response, though it's a well-known technique I found myself reflecting on afterward in terms of whether it's still one worth using given how attitudes toward these kinds of setups may be shifting.

Liv's flash trigger — a new Underwater Light & Magic unit from Jon— ran out of charge because Jon hadn't charged it before I gave it to her. That led to a discussion of Jon’s updated Pro trigger line, which looks identical to earlier models but fires with a faster, stronger beam that reaches full power more quickly. On Nikon Z8 bodies, this allows sync speeds up to 1/250th, a notable improvement over 1/200th. And 1/500th on M43 bodies.

On the Sony A7RVI, however, the Pro trigger didn't resolve the sync speed limitation we discussed in our original review — Sony's simple X-sync setup appears to cap out around 1/200th regardless of trigger. For this trip, I switched to an Underwater Technics trigger on the A7RVI which gives flawless 1/250th sync, full HSS, and both rear and front curtain sync throughout — although for a much higher purchase price. It was completely reliable too.

Jon has also continued refining his gel-filled sync cables, which are notably flexible and now feature redesigned ends that accept light from a wider range of angles — useful when a trigger or camera isn't perfectly aligned. They now come with small clips for attaching along strobe arms.

One more trick from the trip: while setting up off-camera strobe lighting with a model on the Kittiwake wreck, I realized I'd forgotten my usual flash trigger. Instead, we cable-tied one of Jon’s long sync cables to the smallest piece of dive weight we could find — about a pound — let it sink to the wreck, and aimed the cable toward where each photographer would be shooting from. It triggered reliably every time, suggesting that a simple cable-to-weight setup might be just as dependable as a dedicated trigger. I look forward to testing this low-tech solution more in the future.

You can watch the full conversation below.