SeaLife ReefMaster RM-4K review

Matchbox-sized means of making a splash, via a tiny camera encased in waterproof plastic housing

SeaLife ReefMaster RM-4K waterproof camera on a stony waterside
(Image: © Future | Gavin Stoker)

TechRadar Verdict

A toughened, waterproof digital compact camera, or some form of waterproof outer housing to protect the inner camera is a must to shoot underwater, and the second solution is what you get with the SeaLife ReefMaster RM-4K. It provides a matchbox sized digital camera with backplate LCD screen and so-so 14MP stills and 4K video. The camera's housing provides a mega 40m waterproofing, but the potential for user error is worrying: you need to diligently tighten the housing to make it 100% waterproof. SeaLife’s offering is much lighter than most all-in-one waterproof compacts which could sway your decision in its favor, but the reality is there are better alternatives from similarly priced rivals from OM System and Ricoh.


  • +

    Simple to operate

  • +

    Lightweight, palm-sized dimensions

  • +

    Respectable 14MP stills and 4K video

  • +

    Waterproof down to 40 meters


  • -

    Pricey given its plastic-y construction

  • -

    Potential to flood camera if housing not screwed sufficiently tightly shut

  • -

    Small and low-res screen lacks detail

Why you can trust TechRadar We spend hours testing every product or service we review, so you can be sure you’re buying the best. Find out more about how we test.

SeaLife ReefMaster RM-4K: one-minute review

For taking photos underwater, or at the beach or in other situations where your camera could get wet, a dedicated waterproof and toughened compact camera has typically been the preferred solution, at least for consumers. Pro photographers and videographers who own a DSLR or mirrorless camera will alternatively look for specialist underwater housing for their camera, and these tend to be both bulky and pricey.

Falling somewhere in between these options is the small yet outwardly robust SeaLife ReefMaster RM-4K. At its core is a tiny, rectangular GoPro-like digital camera that’s no bigger than a matchbox, which, if used standalone, is not waterproof – though you can use it on land. To use the camera in water you have to secure it inside the provided rubber-sealed, screw-fastened plastic housing. The tiny camera-operation buttons are mirrored on the outer casing with much larger ones, which when pressed essentially operate the smaller buttons within.

SeaLife ReefMaster RM-4K waterproof camera on a stony waterside

(Image credit: Future | Gavin Stoker)

While this doesn’t make for the fastest or most responsive of setups, it works. The camera’s 140-degree fisheye lens enables the capture of up to 14MP stills and 4K video, and the combo is conveniently portable and amazingly lightweight at just 7oz / 200g. The price is comparable to that of a toughened, waterproofed point-and-shoot camera. While this is very much a specific tool for a specific job, you might also want to check out the SeaLife Micro 3.0, which in my opinion this is a slightly neater solution, in that it doesn’t require an external housing for the camera.

SeaLife ReefMaster RM-4K: price and availability

The SeaLife ReefMaster RM-4K is available to buy now, priced at $349.95 / £349.99 / AU$599 – so US buyers are getting a better deal than their British counterparts.

Though the palm-sized camera plus underwater housing combination may appear a little toy-like, its price suggests this is a direct competitor to the all-in-one toughened and waterproofed cameras that are available from the likes of Ricoh, Nikon and Fujifilm, which don’t require a separate waterproof housing. 

The waterproof rating of those compact competitors varies from model to model, and some are more ‘jack-of-all-trades’ devices than dedicated underwater cameras. That being said, if they get covered in sand they can be simply rinsed clean under a tap, as can the housing of the SeaLife ReefMaster RM-4K; however, the camera element needs to stay protected at all times.

Viewed standalone, the SeaLife ReefMaster RM-4K may appear pricey for a matchbox-sized camera with a plastic-y outer housing, but its price is in part justified by its ability to capture 14MP stills and 4K resolution video down to depths of 40 meters. This allows you to capture underwater images and footage in situations where you wouldn’t dare to take your precious DSLR or mirrorless camera. 

SeaLife ReefMaster RM-4K: design

The SeaLife ReefMaster RM-4K comprises a tiny matchbox-sized camera unit that forms the ‘brains’ of the setup, while the rugged plastic outer housing with oversized buttons provides the brawn. 

Once you’ve placed the camera inside the cavity of the housing, you need to screw the unit tightly shut using a red plastic cog to make it waterproof. You’ll need to remove the camera from its housing to recharge its built-in battery via the  supplied USB cable, or to insert or remove the microSD card. Slots for the memory card plus USB and HDMI ports are hidden under a plastic flap on one side of the camera, while two lozenge-shaped buttons on the opposite side are provided for tabbing through on-screen menu options. So far so intuitive.

Because the camera’s LCD screen is a tiny two inches in size, menu icons are necessarily large and obvious. The mode button that also doubles as the power on/off button brings up a brief array of options, while pressing the ‘OK’ button next to it confirms settings changes. This button also has a second use, acting as a shutter release / record button, depending on whether photo or video mode is selected. The buttons need to be pressed quite hard, and sometimes a couple of times, before they do what they’re supposed to, which – to look at it from a more positive angle – at least prevents accidental shots or menu activations. It’s not, though, as quick and responsive as a DSLR or mirrorless camera, so deciding on your settings before going shooting rather than making changes on the fly is recommended.

SeaLife ReefMaster RM-4K: performance

While the 2-inch rear screen on the SeaLife ReefMaster RM-4K is tiny and features a low-ish 230k-dot resolution, it’s bright enough to be able to be viewed clearly through the translucent back of the housing. The small size does make it difficult to assess detail, however, and to tell exactly which parts of your scene or subject are or aren’t in focus. Essentially it’s a case of pointing the camera, pressing the button, and hoping for the best.

While the SeaLife ReefMaster RM-4K is a cute and compact solution for anyone seeking to go diving or snorkeling and capture stills and videos, we’d have preferred a clamp-like fastening mechanism as a belt-and-braces solution alongside the hand-turned plastic cog that screws the back into place, mainly as extra reassurance that the setup is going to stay watertight at all times. 

Most toughened compacts that don’t require extra housing feature the two-step mechanism of a sliding latch and another that turns to make sure their rubber insulated battery/card compartments are doubly protected, and I’d like to have seen something similar here. While the back of the SeaLife’s housing can be screwed tightly shut, and the housing itself feels robust, there still remains room for possible user error.

As for image quality, selecting the maximum 14MP setting delivers images approximately 5MB in size, which exhibit the familiar fisheye-like distortion that’s to be expected the closer you get to your subject. You can alter the field of view from the default 140 degrees to a narrower 100-degree setting that reduces distortion. 

Image quality is generally okay, however, and of a snapshot-like standard, with whatever’s in the center of the frame appearing sharper than detail at the edges. This camera is all about capturing a moment rather than producing gallery-quality results, though, so griping about pixel fringing and the like feels like nitpicking here.

Should I buy the SeaLife ReefMaster RM-4K?

SeaLife ReefMaster RM-4K waterproof camera on a stony waterside

(Image credit: Future | Gavin Stoker)

Buy it if...

You regularly go snorkeling or scuba diving

Though the camera element is perfectly usable outside of its protective housing, the protection provided by the latter is what you’re paying for here.

You want a compact and lightweight camera setup

At just 7oz / 200g the camera and housing combo weighs less than most pebbles we’d pick up at the beach, so it won’t be an unnecessary distraction, hindrance, or compromise in pursuit of capturing imagery where we otherwise could not.

Don't buy it if...

You don’t need a dedicated underwater camera

If you’re only occasionally going to use your camera in the water or in other situations where it might get wet, then a ‘toughened’ point-and-shoot from a range of manufacturers could be a better bet.

You need a zoom lens

This SeaLife solution is all about shooting wide to capture as much of the watery world as possible, without the ability to zoom in on detail. For close-up shots you’ll need to physically move closer to you subject, which might not always be practical or even advisable.

You want a fast and responsive camera

With the latest mirrorless cameras boasting features such as AI-powered auto-focus and subject tracking, the operational responsiveness of the SeaLife Reefmaster RM-4K can’t help but feel a little languid in comparison.

SeaLife ReefMaster RM-4K: also consider


OM System Tough TG-7

An outdoorsy option that will keep shooting whatever the weather, the TG-7 offers a bright f/2 maximum aperture and even built-in GPS. It’s able to keep shooting down to a depth of 15 meters, and is also shockproof, freeze-proof and crushproof  while weighing a pocket friendly 5.3oz / 149g. It captures 12MP stills and 4K video capture to up to 30fps, and while not the sharpest in terms of results it’s not a bad option all told.

Read our OM System Tough TG-7 review


Ricoh WG-80

A waterproof and shockproof point-and-shoot camera that’s ideal as a rugged everyday capture device for the butter-fingered. Like others of its ilk, the small-ish 1/2.3-inch sensor at its heart and equally diminutive lens on the front means that its picture quality isn’t going to compete with your DSLR or mirrorless camera anytime soon, but it does allow you to shoot in dusty, dry and wet conditions where you wouldn’t risk a more expensive camera or smartphone.

How I tested the SeaLife ReefMaster RM-4K

SeaLife ReefMaster RM-4K waterproof camera on a stony waterside

(Image credit: Future | Gavin Stoker)

As I was unable to scuba dive with the camera during my test period and don’t live near the sea, the camera was instead dunked in a river and the local pond, with the resulting images not offering much in the way of enlightenment, save for demonstrating the fact that the controls are large and obvious enough to operate even in poor visibility, or at the end of an extended arm. It also demonstrated that it’s best to configure shooting settings in advance, rather than in the moment.

I also delved into the camera’s shooting menu to adjust its field of view from the default 140 degrees of its fisheye lens to menu-selectable 156-degree and 100-degree settings, as well as trying out the exposure options, which range from the catch-all of auto to manually selectable dedicated settings for deeper water shooting and recording. I also kept a close eye on battery life – SeaLife claims that a fully charged battery is good for a generous 500 shots or around two hours of video, and over the course of a couple of days of use the battery icon on the rear screen had only dipped down by a third.

First reviewed June 2024

Gavin Stoker

When not wrestling wild bears or leaping tall buildings in a single bound, Gavin Stoker can be found editing British Photographic Industry News, the UK's longest running and only photo trade title. He has over 25 years of camera testing and reviewing under his belt.