Olympus OM-D E-M1 vs Sony Alpha A7S III: A Deep Dive into Two Pro Mirrorless Giants

Choosing a professional mirrorless camera involves navigating a labyrinth of specifications, real-world performance, and subjective shooting preferences. The Olympus OM-D E-M1, launched in 2013, and the Sony Alpha A7S III, announced seven years later in 2020, represent distinctly different eras and philosophies in mirrorless design. Yet, both command respect from enthusiasts and professionals alike, albeit for divergent reasons.

Having spent over 15 years rigorously testing cameras across diverse photographic disciplines and scenarios, I’m excited to unpack these two models with you. This comparison is grounded in exhaustive field testing and technical evaluation, covering everything from sensor technology and autofocus to ergonomics and video performance. By integrating key insights and benchmark data, this review aims to empower you to make a confident, informed choice based on your creative needs and budget.

First Impressions and Physical Considerations: Size, Build, and Handling

Let’s begin by comparing the fundamental tactile experiences, which often shape long-term user satisfaction.

The Olympus E-M1 feels compact and lightweight next to the larger Sony A7S III

The Olympus E-M1 is undeniably compact and lightweight at just 497 grams with dimensions measuring approximately 130x94x63mm. Olympus’s Micro Four Thirds (MFT) system inherently favors portability without sacrificing the robustness expected from a pro-level tool. Constructed with environmental sealing, the E-M1 resists dust and splashes, making it well suited for field shooters who prioritize mobility and resilience beyond studio walls.

Contrastingly, the Sony A7S III weighs around 699 grams and has a more substantial grip and deeper body at 129x97x81mm. This full-frame camera’s build quality is also weather-sealed, reflecting Sony’s commitment to professional durability. The enhanced size facilitates superior handling, especially valuable when using heavier telephoto lenses or when shooting handheld for extended durations.

Ergonomically, the E-M1 offers a tilting 3-inch LCD and a high-resolution EVF but lacks illuminated buttons, which can be a minor impediment in low-light operation. The A7S III sports a fully articulating 3-inch touchscreen with a considerably higher pixel count for crisp image review and flexible shooting angles, plus illuminated controls for intuitive operation in dark conditions.

Control layout distinction shows Olympus’s traditional approach vs Sony’s modern interface

Sony’s interface benefits from more customizable function buttons and a joystick, enhancing the speed and precision of autofocus point selection and menu navigation. In contrast, Olympus retains a more classical dial-heavy approach, which some find satisfying but others may see as limiting compared to the quick-access customization on Sony’s body.

Summary: The Olympus E-M1 wins on portability and ease of carry during travel and street shooting; the Sony A7S III's larger, more rugged body and advanced control interface favor demanding professional environments and long shoots.

Sensor Technology and Image Quality: The Heart of the Camera

One cannot overlook the decisive role sensor characteristics play in image rendering and versatility.

A visual comparison of sensor sizes: Olympus’s Micro Four Thirds vs Sony’s Full Frame

Fundamentally, the Olympus E-M1 features a 16MP Four Thirds-sized CMOS sensor (17.3 x 13 mm), adhering to a 2.1x crop factor. The smaller sensor allows for highly compact lenses and excellent in-body stabilization but comes with inherent limitations in low-light performance and depth of field control.

At the other end of the spectrum, the Sony A7S III boasts a 12MP full-frame BSI-CMOS sensor (35.6 x 23.8 mm). While lower in resolution, this sensor excels at delivering extraordinary sensitivity and dynamic range, underscored by a maximum native ISO of 102,400 (expandable to an astounding 409,600). This makes Sony’s offering a powerhouse for low-light and video-centric shooters.

In laboratory measurements and real-world testing, the Sony A7S III outperforms the E-M1 in every critical metric:

• Dynamic range: Sony’s sensor clocks in at approximately 13.3 EV compared to Olympus’s 12.7 EV, revealing an ability to recover shadows while preserving highlights better.
• Color depth: Both provide rich color, but Sony marginally leads at 23.6 bits over Olympus’s 23.0 bits.
• Low light sensitivity: The A7S III scores a remarkable 2993 ISO equivalent on DxOMark’s low-light test, vastly superior to the E-M1’s 757.

The tradeoff for Sony users is lower native resolution (12MP versus Olympus’s 16MP), which may marginally impact large-format landscape or portrait printing sizes but is offset by lower noise and finer tonal gradations at high ISO.

Olympus’s antialiasing filter reduces moiré but at the expense of some sharpness, while Sony keeps the filter, trusting higher-quality optics and sensor design to manage artifact control.

Summary: The Sony A7S III’s full-frame sensor dramatically outclasses the Olympus E-M1’s Four Thirds sensor in dynamic range and high ISO performance, crucial for professionals shooting in challenging light. The E-M1 remains a viable option for photographers valuing resolution and portability within daylight or moderate indoor conditions.

Autofocus Systems and Shooting Responsiveness

Sharpness is often secured in-camera by autofocus (AF) technologies that blend speed, accuracy, and tracking sophistication.

The Olympus E-M1 uses a hybrid AF system featuring 81 focus points combining contrast detection with phase detection. This implementation was progressive for its time, offering decent face detection and continuous AF tracking. However, it lacks animal eye detection and the sheer point density critical in fast-paced situations.

In contrast, the Sony A7S III boasts 759 phase-detection AF points - an order of magnitude increase - complemented by contrast-detection AF in a hybrid layout optimized for subject tracking reliability. Sony integrates real-time face and eye detection tailored for humans as well as animals (dogs, cats, birds), and its AI-driven autofocus excels at tracking unpredictable motion with remarkable confidence.

Both cameras can shoot continuous bursts at 10 frames per second, but Sony’s buffer and processing pipeline afford longer shooting sequences without slowdown, vital for wildlife and sports photography.

Touchscreens compared: Olympus’s tilting 3.0” vs Sony’s fully articulating 3.0”

Touchscreen AF point selection is intuitive on both cameras, but the A7S III’s articulating rear display also facilitates easier framing and focusing from unconventional angles, a boon for macro and video operators.

Practical testing revealed:

• Olympus AF works well for static subjects and moderately paced action but may lag in dense environments.
• Sony’s AF system shines in continuously changing scenes and adverse lighting, maintaining focus lock with minimal hunting.

Summary: The Sony A7S III's autofocus system is a leap ahead, particularly for wildlife, sports, and video, while Olympus offers respectable performance suitable for portrait and casual action photography.

Image Stabilization and Low-Light Capability

Both cameras feature 5-axis sensor-shift image stabilization, a crucial feature that increases handholding usability across shutter speeds and focal lengths.

While the Olympus E-M1 popularized sensor-based 5-axis IS with up to 5 stops of shake correction, the A7S III builds on this technology with optimized algorithms enhancing stabilization particularly for handheld video and high-resolution EVF operation.

When combined with Sony’s low-noise sensor, the stabilization system supports handheld shooting at shutter speeds multiple stops slower than normally possible. Olympus users will appreciate the system but must temper expectations when the smaller sensor size inevitably increases noise at high ISO compared to Sony’s full-frame sensor.

Comprehensive Photography Discipline Breakdown

The following section evaluates these cameras across 10 key photography genres based on hands-on shooting experience and comparative testing results.

Portrait Photography: Skin Tones, Bokeh, and Eye Detection

• Olympus E-M1: The smaller sensor yields deeper depth of field at equivalent apertures, impacting subject-background separation. Its skin tone rendering is natural with color science tuned slightly warm, which can be flattering. However, bokeh is less creamy compared to full-frame cameras due to sensor size. Eye AF works well but lacks the precision and animal eye detection of newer models.

• Sony A7S III: The full-frame sensor offers smoother background blur and exceptionally accurate eye-detection AF - even on moving subjects and low light - greatly speeding up workflow when photographing portraits in dynamic setups.

Landscape Photography: Resolution, Dynamic Range, and Environmental Sealing

• Olympus E-M1: Although chunky erosion-prone landscapes demand resolution and detail, the 16MP sensor captures ample detail for prints and digital use. Environmental sealing allows shooting in light rain or dusty environments. Dynamic range is commendable but not class-leading.

• Sony A7S III: The 12MP resolution may seem low, but larger sensor pixels capture stunning tonal depth and highlight retention, critical in high-contrast landscapes. The camera's full weather sealing and robust battery enable extended outdoor shoots.

Wildlife Photography: Autofocus Speed, Telephoto Performance, and Burst Rates

• Olympus E-M1: Smaller sensor and 2.1x crop factor allow the use of smaller, lighter telephoto lenses cropping farther into the action. Nonetheless, AF speed and tracking are only average, limiting fast subject acquisition.

• Sony A7S III: Superior AF system and plentiful lens options (native Sony E and third-party) excel here. The camera handles fast-moving subjects and continuous bursts gracefully, critical when moments vanish in a blink.

Sports Photography: Tracking Accuracy, Low Light, Frame Rates

• Olympus E-M1: 10fps burst is a strong point but limited buffer size and slower AF tracking reduce potential. Low light performance constraints appear in big arenas.

• Sony A7S III: Advanced tracking AF alongside 10fps shooting with deep buffer suits virtually all sports settings. The ability to shoot reliably at very high ISO levels extends use into indoor arenas.

Street Photography: Discreteness, Low Light, Portability

• Olympus E-M1: Compact size and quiet operation make it discreet and portable - ideal for street shooters. Low light capacity suffices for twilight scenes.

• Sony A7S III: Bulkier and heavier, reducing discretion, but unbeatable low light sensitivity helps if you prioritize image quality over size.

Macro Photography: Magnification, Focusing Precision, Stabilization

• Olympus E-M1: Paired with Olympus’s excellent macro lenses plus sensor-based stabilization and focus bracketing, the E-M1 offers remarkable macro capabilities.

• Sony A7S III: Focus bracketing options are absent, but robust stabilization, high ISO headroom, and stunning video quality allow captivating macros in natural light.

Night/Astro Photography: High ISO Performance, Exposure Modes

• Olympus E-M1: Limited by sensor size, night images have higher noise, and limited max ISO.

• Sony A7S III: Excels in astrophotography with its low read noise, superb high ISO handling, and exposure controls suited for long exposures - amazingly useful for astro shooters.

Video Capabilities: Recording Specs, Stabilization, and Audio

Olympus E M1 front Olympus E M1 screen back Sony A7S III front Sony A7S III screen back

• Olympus E-M1: Offers Full HD (1920 x1080) video up to 30fps. Stabilization aids handheld video, but video codecs and bitrates are modest.

• Sony A7S III: Bears state-of-the-art 4K recording up to 120fps, with multiple codecs (XAVC S, H.264, H.265) and advanced audio inputs including headphone monitoring, making it a favorite for filmmakers and hybrid shooters.

Travel Photography: Versatility, Battery Life, Size, Weight

• Olympus E-M1: Compactness and lighter weight favor travel ease. Battery life is moderate (~350 shots), requiring backups on extended trips.

• Sony A7S III: Bigger body and heavier but better battery longevity (~600 shots) and dual card slots offer greater reliability for long journeys.

Professional Work: Reliability, File Formats, Workflow Integration

• Olympus E-M1: Supports RAW and manual controls essential for professional needs but limited by older interfaces and USB 2.0 speeds.

• Sony A7S III: Superior file handling, faster USB 3.2 interface, and dual card slots grant a more modern workflow and data security, critical in professional environments.

Connectivity, Storage, and Power Management

Sony’s inclusion of Bluetooth, NFC, and dual SD/CFexpress Type A card slots addresses modern connectivity and redundancy needs, while Olympus provides single-card slot SD support and built-in Wi-Fi but lacks Bluetooth or NFC.

Battery technology has progressed between these models, with Sony’s NP-FZ100 batteries delivering nearly double the shots per charge compared to Olympus’s BLN-1, mitigating interruptions during demanding shoots.

Price and Value Analysis

The Olympus E-M1 originally retailed around $799, representing an excellent entry into professional mirrorless photography within the Micro Four Thirds ecosystem boasting over 100 native lenses.

The Sony A7S III commands a hefty $3499 price tag, reflecting innovations that push conventional performance boundaries - especially for video and low-light domains.

For budget-conscious buyers focused on portability and still photography in controlled environments, Olympus presents compelling value; Sony’s A7S III is the gold standard for low-light, video, and professional assignments that justify premium investment.

Final Verdict: Who Should Choose Which?

Choose the Olympus E-M1 if:

• You prioritize a compact, lightweight system for travel, street photography, or macro work.
• Your shooting style revolves mostly around stills with moderate action and controlled lighting.
• You desire access to a rich Micro Four Thirds lens catalog and well-implemented in-body stabilization.
• Budget constraints preclude the purchase of higher-end full-frame bodies.
• You accept modest video capabilities focused on 1080p.

Opt for the Sony A7S III if:

• Your work demands excellence in low-light shooting, wildlife, sports, or astrophotography.
• Video production is a core focus - 4K120p capabilities combined with best-in-class image stabilization and audio features are critical.
• You require a professional workflow with dual card slots, fast data transfer, and high-capacity batteries.
• You want the best autofocus system available that includes animal eye detection and AI-enhanced tracking.
• Budget is flexible, and you seek longevity and future-proofing in your camera investment.

Summary and Recommendations

Both the Olympus OM-D E-M1 and Sony Alpha A7S III remain exemplary pro mirrorless cameras, yet their target audiences and strengths differ vastly. Olympus delivers a timelessly portable and versatile tool optimized for daylight and moderate speed photography with superb stabilization, while Sony defines the modern benchmark in video, low-light, and autofocus sophistication anchored by its impressive full-frame sensor.

Your decision should reflect your genre preference and priorities: the E-M1 shines in portability and lens diversity within the Micro Four Thirds realm, whereas the A7S III conquers demanding low-light scenarios, fast-action subjects, and professional video work with unrivaled technical prowess.

In conclusion, both cameras affirm their brands’ legacies - Olympus as a champion of compact system versatility and Sony as a leader in sensor innovation and hybrid imaging performance.

Choosing either camera means engaging with a powerful creative ally; understanding their unique strengths ensures the right match for your photographic vision.

This detailed, experience-driven comparison aimed to provide clarity and confidence for photography enthusiasts and professionals navigating these pro mirrorless stalwarts.