The Sony A7S III marked a breakthrough for many underwater video shooters. It quickly became a top choice in 2021 for those seeking exceptional 4K video capabilities with flexible workflow options and reliable post-processing performance. Its low-light capability stood out, particularly for underwater use, where it delivered clean video even at ISO levels exceeding 12,800. This performance in dimly lit underwater environments made it a preferred choice among videographers exploring marine life.
Shortly after the release of the A7S III, Sony introduced the FX3. The FX3 shares the same internal specifications as the A7S III but is housed in a body designed to align with Sony’s cinema line. This raises a natural question for underwater video creators: why release essentially the same camera in a different body, and what implications does this have for underwater use?
Although this review does not include a dive test with the FX3, the insights provided are valuable. Most information about the camera’s performance aligns with what has already been documented for the A7S III. However, there are new considerations specific to the FX3 that make it a compelling option for underwater videographers. The following sections examine why the FX3 could be an even better choice for some underwater video professionals.
Key Differences Between Sony FX3 and Sony A7S III
Internally, the Sony FX3 is virtually identical to the Sony A7S III. They offer the same image quality, recording capabilities, and video functionality. However, the external differences in body design introduce features that may or may not be relevant underwater. These differences become crucial when choosing between the two for specific shooting conditions.
The FX3 is slightly smaller in body size than the A7S III and does not include a viewfinder. It comes with a detachable handle featuring dual XLR/TRS audio terminals. While these are excellent additions for audio capture in a studio or surface environment, they hold little value in underwater videography where the handle cannot be used.
Another distinguishing feature is the zoom lever on the FX3. This lever supports only two specific Sony lenses: the FE PZ 28-135mm f/4 and the FE C 16-35mm T/3.1. Among these, only the latter may find relevance in underwater use due to its wide-angle capability.
The FX3 is also equipped with multiple tally lights on the body. These indicators provide visual confirmation when the camera is recording. While not essential, they add convenience for users in certain environments.
Perhaps the most impactful hardware addition is the built-in cooling fan. While the A7S III is known for handling heat well, it can experience overheating under continuous 4K/120p recording—especially in enclosed underwater housings. For shooters focused on extended slow-motion sequences, the FX3’s cooling system offers a potential advantage in maintaining performance during long takes.
Additional modifications include mounting thread holes for accessories, though these are largely unnecessary for underwater operation. Price-wise, the FX3 is listed at $3899, which is higher than the $3499 price tag of the A7S III. This price increase is mostly due to the included handle and audio adapter, which are irrelevant for underwater shooters.
Choosing Between the Sony FX3 and Sony A7S III for Underwater Use
When deciding between the Sony FX3 and the A7S III for underwater videography, many of the external differences lose their significance. Features like the handle, XLR inputs, and accessory thread holes are generally unusable underwater. However, a few key factors tip the scale in favor of the FX3 for specific use cases.
First, the Nauticam underwater housing for the FX3 is marginally smaller and lighter than the one designed for the A7S III. The FX3 housing weighs approximately 1.97 kg, while the A7S III housing comes in at 2.7 kg. This weight reduction can be advantageous when managing gear during travel or long dives. However, the absence of a viewfinder on the FX3 also means that underwater users cannot utilize an external magnified viewfinder—an important consideration for framing and composing shots.
Another important factor is overheating. Some A7S III users have reported that recording 4K at 120 frames per second for extended periods—such as 20 minutes or more—can cause the camera to overheat. While most underwater shooters do not need such long, slow-motion clips, those who do may benefit from the FX3’s internal fan, which provides enhanced thermal management for longer, uninterrupted shooting sessions.
In summary, for users focused purely on video who are not dependent on using an external viewfinder, the FX3 presents a slightly more efficient option with the potential for longer recording times and a lighter underwater housing.
Underwater Housings for the Sony FX3
Only a few underwater housings are currently available for the FX3, but each offers different advantages depending on the user’s needs and budget. The three main options include housings from Nauticam, Marelux, and Ikelite. All are designed to offer access to essential controls, protection against water pressure, and compatibility with various lenses and accessories.
The Nauticam housing is the lightest among the three and is constructed from solid anodized aluminum. This makes it durable and resistant to corrosion in saltwater conditions. It includes a leak detection system, and supports external HDMI monitors via 1.4 and 2.0 cable connections. The locking port system is intuitive, allowing for quick lens and port changes, while remaining compatible with Nauticam optics.
The Marelux FX3 housing is a more recent addition. Made from high-grade aluminum alloy, it is built to withstand demanding dive environments. Marelux prioritizes ergonomic design, placing controls in user-friendly locations for intuitive operation even when wearing gloves. This housing is suitable for professionals looking for a rugged solution that balances functionality with a streamlined design.
The Ikelite FX3/FX30 housing represents an affordable alternative made from polycarbonate. It is depth rated to 200 feet and provides full access to camera functions. It includes a standard M16 bulkhead with the option for an M24 bulkhead, allowing the use of external monitors and additional accessories. Ikelite’s dry lock port system ensures compatibility with a wide range of full-frame E-mount lenses. Though not as rugged as its metal counterparts, it is a solid option for hobbyists or those working within budget constraints.
Diving Deeper – Underwater Performance of the Sony FX3
The true strength of the Sony FX3 lies in its internal architecture, inherited from the Sony A7S III. At the heart of this camera is a 12.1-megapixel full-frame back-illuminated CMOS sensor, paired with Sony’s advanced BIONZ XR image processor. This combination allows the FX3 to capture extraordinarily clean and detailed video, even in low-light conditions. For underwater videographers, where ambient light is often limited, this is a critical advantage.
The FX3 records 4K video at up to 120 frames per second with 10-bit 4:2:2 color sampling, delivering a balance of high resolution and cinematic motion. It supports internal recording in All-Intra and Long GOP codecs, as well as external RAW recording via HDMI. These formats allow for flexible editing and color grading workflows, giving creators full control in post-production.
This level of video fidelity makes the FX3 a reliable tool for capturing complex underwater scenes—whether it’s filming the fine movements of macro subjects like nudibranchs or the fluid motion of large marine animals in open water. With support for S-Log3, HLG, and S-Cinetone picture profiles, the FX3 empowers users to preserve dynamic range and maintain consistent color tones in various lighting conditions.
Low Light Dominance and ISO Performance
One of the most impressive features of the Sony FX3 is its low-light sensitivity. With a native ISO range of 80–102,400 (expandable to 409,600), the FX3 can shoot in dim environments with reduced noise and preserved detail. This is particularly useful when diving below 20 meters, where natural light drops significantly and artificial lighting becomes necessary.
Many underwater video shooters are already accustomed to using high-powered video lights to illuminate scenes, but these lights have limitations. In turbid water or when shooting wide-angle scenes, even strong lights may not fully compensate for the lack of ambient light. The FX3 bridges this gap with its ability to shoot at ISO levels above 12,800 without introducing severe noise artifacts.
In cave diving, night diving, or in shaded reef environments, the FX3 continues to deliver clean footage where other cameras struggle. This high-ISO performance helps maintain detail in the shadows and reduces the need for overexposure that could lead to blown-out highlights in sunlit areas or artificial backlighting.
Dynamic Range and Color Science Underwater
Dynamic range is an essential factor for capturing underwater scenes with realism. The FX3 delivers over 15 stops of dynamic range when recording in S-Log3, allowing it to handle the high-contrast environments typical of underwater spaces. The surface can be extremely bright, while deeper water and crevices in the reef may appear dark in contrast. Managing these extremes is essential to avoid losing information in highlights or shadows.
The FX3’s color science also plays a key role. Sony’s S-Cinetone profile, introduced in their cinema line, provides pleasing skin tones and natural color rendering straight out of the camera. While color correction is often required in underwater footage due to the loss of red wavelengths and shifting color temperatures, starting with a naturally balanced image is an advantage. S-Cinetone footage often requires less aggressive grading, making it ideal for quick delivery workflows or projects with tight turnarounds.
For divers who prefer maximum flexibility in post-production, shooting in S-Log3 or RAW provides even greater control. These modes capture flat profiles that retain extensive highlight and shadow detail. With proper white balancing and grading, they can be color-corrected to restore the original scene’s tones—even when significant color loss occurs at depth.
Autofocus Performance in the Underwater Environment
Autofocus is a challenging feature to master in underwater video due to the shifting motion of both the subject and the diver. However, the FX3 performs admirably in this area. It inherits Sony’s excellent Real-time Eye AF and Real-time Tracking systems. Though these features are primarily intended for land-based subjects like humans and animals, they also help track fish and marine creatures with impressive consistency.
The camera offers 627 phase-detection points and contrast-detection autofocus working in tandem. When paired with a fast, responsive lens like the Sony 14mm f/1.8 or 24mm f/1.4, the FX3 can track moving subjects with remarkable precision.
That said, autofocus underwater depends heavily on available contrast, water clarity, and lighting. In murky or low-light conditions, manual focus or back-button focus may be preferable. Fortunately, the FX3 supports focus peaking and magnification tools that assist divers in achieving critical focus manually when autofocus struggles.
The FX3 also allows customization of focus speed and transition sensitivity. This gives users control over how quickly the camera racks focus between subjects, which can add a cinematic feel to underwater sequences. Slow focus transitions are often more visually pleasing in documentary work or creative videography.
Internal Cooling and Long Recording Times
One of the key differentiators between the FX3 and the A7S III is the FX3’s internal active cooling system. This cooling fan, housed inside the camera body, allows for extended recording sessions without the risk of overheating. While the A7S III performs well in most conditions, underwater housings trap heat, and high-bitrate recording at 4K/120p can push thermal limits.
The FX3 excels in this environment, maintaining stable internal temperatures even during long dives and continuous shooting. This makes it ideal for filming lengthy behaviors such as spawning events, group hunting, or schooling fish interactions—events that can take time and patience to document.
For slow motion enthusiasts, the FX3 provides peace of mind. Continuous recording in 4K at high frame rates places a significant processing load on the camera, which can cause overheating in other models. The FX3’s design avoids this limitation, making it a more reliable tool for capturing time-intensive underwater scenes.
Ergonomics and Underwater Handling
The ergonomics of the FX3 are influenced by its cinema lineage. The camera lacks a traditional electronic viewfinder, which makes little difference for underwater users who rely on external monitor connections. Its slightly smaller footprint compared to the A7S III contributes to lighter underwater housing designs, a practical benefit when traveling or working in current-heavy dive locations.
Despite its compact size, the FX3 features full-size HDMI ports, multiple function buttons, and a rugged build that withstands tough environments. These features, while not always utilized underwater, signal Sony’s commitment to professional use and long-term durability.
In summary, the FX3’s underwater performance is a reflection of its excellent sensor, robust processing capabilities, and video-centric design. Whether documenting macro life in shallow reefs or chasing wide-angle subjects on deeper dives, this camera delivers consistent and cinematic results that professionals demand.
The Role of Underwater Housings in Maximizing FX3 Performance
Selecting the right underwater housing is as crucial as choosing the camera itself. An underwater housing protects the camera from pressure, moisture, and impact while ensuring access to essential controls. For a high-performance camera like the Sony FX3, housing quality directly affects usability, stability, and image composition underwater.
Not all housings are created equal. Material, design, control accessibility, and support for accessories like external monitors or vacuum leak systems all influence shooting efficiency. Fortunately, several reputable manufacturers have developed underwater housings tailored to the Sony FX3, including Nauticam, Marelux, and Ikelite.
Each housing caters to different needs. Some prioritize compactness and travel-friendliness, while others offer robust expandability for professional filming rigs. The following sections evaluate the strengths and use cases of the top FX3 underwater housing options currently available.
Nauticam FX3 Underwater Housing: Lightweight Professional Power
The Nauticam FX3 housing is an ideal match for videographers who require a lightweight yet professional-grade solution. Weighing just 1.97 kg, it’s significantly lighter than the Nauticam housing for the A7S III. The smaller size results in easier transport, quicker setup, and less strain when handling the rig underwater.
Built from solid anodized aluminum, the housing is corrosion-resistant and designed for depth ratings far beyond recreational limits. It includes Nauticam’s signature features like an integrated vacuum system and leak detection alert—key additions for ensuring dive safety.
Button layout and ergonomic design are thoughtfully executed. Users can operate essential controls like white balance, focus, and shutter speed without removing hands from the grip. The housing supports full-size HDMI connections, allowing integration with external monitors—an essential tool for serious video shooters seeking precise framing and exposure monitoring underwater.
One consideration is the absence of a viewfinder due to the FX3’s design. While some photographers prefer external optical viewfinders, video shooters often favor external monitors, making this a negligible trade-off.
Marelux FX3 Underwater Housing: Innovative and Rugged
The Marelux FX3 housing is one of the newer options on the market. Known for its durable construction, Marelux builds housings from high-grade aluminum alloy with attention to both form and function. The housing is sealed with dual O-rings and tested to withstand depths beyond 100 meters.
Its standout feature is the modular design. Users can customize the housing with handles, trays, and additional ports to suit various underwater shooting styles. The control layout is intuitive, and levers are placed for easy access even with gloved hands.
Marelux also emphasizes aesthetics. The sleek, matte-black finish resists scratches and fingerprints. But it’s not just about looks. The internal stabilization of the camera complements the housing’s ergonomic balance, resulting in smooth footage and comfortable handling during extended dives.
This housing supports sync cables for lighting, HDMI monitor connections, and bulkhead adaptors for professional accessories. It’s a great fit for filmmakers who want the flexibility to expand their rig as needed.
Ikelite FX3/FX30 Underwater Housing: Budget-Friendly Versatility
For divers seeking a more affordable housing without sacrificing performance, the Ikelite FX3/FX30 housing is a compelling option. Made from polycarbonate instead of aluminum, it reduces costs while maintaining reliable protection. It is depth rated to 200 feet and features a transparent back, allowing users to visually inspect camera placement and seals.
While it may not have the same premium feel as Nauticam or Marelux housings, Ikelite provides full access to FX3 controls. Its M16 and optional M24 bulkheads make it compatible with external monitors and accessories. The dry lock port system ensures compatibility with most E-mount full-frame lenses, including popular wide-angle and macro choices.
Ikelite offers a good balance for hobbyists, entry-level professionals, or those who want a lightweight setup for travel without the higher cost of metal housings.
Port and Lens Compatibility for Underwater FX3 Shooters
Lens selection plays a vital role in the quality and type of underwater footage captured. Wide-angle and macro lenses are the staples of underwater videography, each offering unique perspectives. The FX3 supports a wide array of E-mount lenses, and most housings provide ports and extensions for these lenses.
Wide-angle lenses like the Sony 14mm f/1.8 or the FE 16-35mm f/2.8 GM offer expansive views that are ideal for reef scenes, wreck exploration, or documenting large marine species. Dome ports help correct distortion and maintain field of view when shooting underwater.
For macro shooting, the Sony 90mm f/2.8 Macro G OSS is a popular choice. Flat ports maintain sharpness and magnification, allowing divers to focus on tiny subjects like shrimp, nudibranchs, and coral polyps. Many housings also support wet diopters or macro converters for increased magnification.
Using the FX3’s focus assist tools and custom buttons, shooters can confidently use both manual and autofocus lenses underwater. The flexibility in lens options allows creators to tailor their rig to the type of dive or story they aim to capture.
Enhancing the Sony FX3 with Accessories and Underwater Workflow Tips
To truly unlock the power of the Sony FX3 underwater, it is crucial to pair it with the right accessories. These tools not only enhance the quality of footage but also improve handling, workflow, and safety during dives. Below are key categories of accessories that are commonly used by underwater cinematographers.
Video lights are among the most important accessories. No matter how capable the FX3 is in low-light conditions, artificial lighting is necessary to restore color and bring vibrancy to underwater scenes. High-powered continuous video lights from brands like Keldan, Light & Motion, or Bigblue offer color temperatures in the daylight range and brightness levels exceeding 10,000 lumens. These lights are essential for filming in dark reef crevices or at night.
Color correction filters help rebalance the color spectrum underwater, especially in natural light. Red and magenta filters are often used at different depths and in various water types to compensate for the rapid loss of warm tones. While post-processing can restore color, using filters at capture reduces the need for aggressive grading and retains more natural hues.
External monitors and recorders, connected via HDMI, enhance visibility and composition. The FX3 supports clean HDMI output, which makes it compatible with external monitors from manufacturers such as SmallHD, Atomos, and Nauticam. These monitors are invaluable for evaluating focus, exposure, and framing—especially when shooting in bright conditions where the camera’s LCD can be hard to view.
Buoyancy arms and floats are vital to balance the rig. The FX3 with housing, lights, and accessories can be quite heavy underwater. Using float arms helps achieve neutral buoyancy, reducing diver fatigue and improving stability during handheld shooting.
A vacuum leak detection system is another must-have for professionals. Most modern housings from Nauticam and Marelux include this feature by default. It allows users to check the housing’s watertight seal before diving, preventing catastrophic camera damage from floods.
Spare batteries and large-capacity memory cards are also important. While the FX3 has solid battery life, continuous 4K recording, especially at 120 fps, is demanding. Carrying multiple batteries and using CFexpress Type A or V90-rated SD cards ensures uninterrupted filming and rapid data transfers after the dive.
Pre-Dive Setup and Custom Settings for Underwater Use
Proper camera setup before entering the water is essential for efficient shooting. Underwater environments do not allow for extensive changes to settings once submerged, so everything must be dialed in beforehand.
Assigning custom function buttons on the FX3 makes it easier to access white balance, focus modes, or ISO settings. These buttons should be mapped based on personal preferences and what the housing allows you to control externally.
Custom white balance is extremely important. Water absorbs different wavelengths of light at varying depths, with reds disappearing first. Creating a manual white balance based on a white or grey card at depth produces much better results than relying on auto white balance. This is especially important when not using artificial lighting.
Setting the correct picture profile before diving is also crucial. Many underwater shooters prefer S-Log3 for its wide dynamic range and post-production flexibility. Others might choose S-Cinetone for a more natural look straight out of the camera. These profiles should be tested and evaluated before the dive to determine which workflow best suits your project.
For focus, it is best to decide in advance whether you will be using continuous autofocus, manual focus with peaking, or a hybrid approach. This decision should be based on the subject type and visibility conditions. Setting the right focus area mode—such as center, zone, or wide—improves tracking performance underwater.
It is also helpful to set up file naming, dual card recording, and audio inputs (even if unused underwater) to ensure footage is organized properly. These settings save time during editing and improve backup reliability.
Shooting Techniques for FX3 Underwater Video
Achieving cinematic underwater footage with the FX3 involves both technical and creative considerations. Smooth camera movements, proper composition, and an understanding of light behavior underwater are essential to producing professional results.
Neutral buoyancy is the foundation of good camera work. Without it, footage may appear shaky, jerky, or unstable. Practicing buoyancy skills and fine-tuning with float arms ensures smoother camera operation.
Using wide-angle lenses allows the shooter to get close to the subject while still capturing expansive backgrounds. This technique reduces the amount of water between the subject and the camera, preserving clarity and contrast.
Slow motion, enabled by 120 fps recording, adds drama to fast-moving marine life. This is particularly effective with schooling fish, predator-prey interactions, or dynamic swimming behaviors. The FX3’s ability to capture these events in 4K resolution without cropping means videographers retain full frame coverage and image quality.
Lighting placement is also important. Avoid pointing lights directly at reflective surfaces or particles in the water to reduce backscatter. Positioning the lights off to the sides and using diffusers creates a soft, even illumination.
Creative shot planning improves storytelling. Wide establishing shots, medium shots of marine animals, and close-ups of texture or behavior all help build visual narratives. The FX3’s compact design allows it to maneuver easily through coral reefs, wrecks, and caves for versatile compositions.
Post-Processing and Editing Workflow
Footage from the Sony FX3 is well-suited for professional editing pipelines. Files recorded in 10-bit 4:2:2, All-Intra, or ProRes RAW can be color graded and manipulated extensively without losing detail or introducing artifacts.
Color correction is a vital step for underwater footage. Using vector scopes and waveforms, editors adjust white balance, contrast, and saturation to restore natural colors lost during the dive. When filming in Log profiles, LUTs (Look-Up Tables) are often used as a base for consistent looks.
Noise reduction is another common task. Even though the FX3 performs well at high ISOs, deeper footage may require gentle noise reduction, especially in shadow regions. Applying this selectively helps retain sharpness and fine detail.
Stabilization can be applied either in-camera or during post-production using software tools like Adobe Premiere Pro or DaVinci Resolve. The FX3's internal 5-axis image stabilization helps, but additional stabilization in post ensures ultra-smooth visuals.
Sound editing is less common for underwater-only sequences but becomes relevant when ambient audio is recorded on the surface or during topside interviews. Syncing audio from external recorders, adjusting levels, and applying EQ complete the audio track for full documentary productions.
Final delivery formats should be determined by the target platform. Whether it's YouTube, film festivals, or broadcast, exporting in the correct resolution, bitrate, and codec ensures compatibility and visual integrity.
Conclusion:
The Sony FX3 stands as one of the most capable and thoughtfully designed video cameras available today for underwater use. By combining the high-performance sensor and processor of the A7S III with features tailored for cinematography, Sony has created a hybrid that appeals to both field shooters and creative professionals.
Its standout qualities—superb low-light performance, internal 4K/120p recording, dynamic range, and advanced autofocus—address many of the challenges faced underwater. Add to that the improved heat management through an active cooling fan, and you get a camera that can endure long, demanding shoots in thermally restrictive housings.
While many of the cinema-focused features, like the XLR handle or multiple thread mounts, hold little value underwater, the FX3’s internal strengths and compact size make it a compelling choice for video-centric divers. The availability of professional-grade housings from Nauticam and Marelux, as well as the budget-friendly Ikelite option, ensures a housing is available for every type of user.
Choosing between the FX3 and A7S III ultimately depends on priorities. Those who want the option of using a viewfinder or saving a bit of money may prefer the A7S III. But for pure video shooters who value extended recording times, a lighter rig, and no compromises in video quality, the FX3 is an investment that pays off.
In the end, the Sony FX3 is not just a camera repackaged in a cinema body. It is a powerful underwater video system that empowers divers to capture marine life with stunning realism, emotion, and clarity. Whether documenting marine biology, creating artful films, or producing commercial dive content, the FX3 rises to the challenge and delivers excellence, dive after dive.