Olympus E-M10 III vs. Pentax 645D: A Crossroad in Mirrorless and Medium Format DSLR Worlds

When stepping into the realm of camera comparison, it’s tempting to pit similar models head-to-head, but today we take a less-traveled path: matching the Olympus OM-D E-M10 Mark III, a sleek mirrorless Micro Four Thirds contender, against the Pentax 645D, a heavyweight in the medium format DSLR arena. Sure, they come from vastly different lineages and price brackets, but this comparison reveals fascinating insights about what different camera systems deliver - and to who.

Having spent years rigorously testing cameras across diverse photography disciplines and settings, I’ve learned that understanding each model’s strengths in context is what ultimately informs sound decisions. This article combines hands-on experience, technical evaluation, and a clear-eyed look at real-world usage to help photographers ranging from enthusiasts to pros decide which niche each camera carves out for itself.

Let’s dive in.

First Impressions and Handling: Small Wonder vs. Stalwart Titan

At first glance - well, literally when held in your hand - you’ll notice these two cameras couldn’t be more different in physical presence.

The Olympus E-M10 III tips the scales at a featherweight 410 grams with body dimensions of 122 x 84 x 50 mm. It’s very much an entry-level mirrorless camera designed for portability and spontaneous shooting. Its compact build translates to nimble handling that’s especially appealing for street and travel photographers who prioritize ease of carry.

In stark contrast, the Pentax 645D is a chunky 1480 grams and significantly larger at 156 x 117 x 119 mm. This is a professional medium format DSLR built for studio robustness and field durability, featuring extensive weather sealing and a heft that implies reliability.

Ergonomically, the Olympus sports a responsive tilting touchscreen LCD and an electronic viewfinder (EVF) with 2,360k-dot resolution and 100% coverage, catering to high usability in live view and video. The Pentax pairs a fixed 3-inch LCD without touch with an optical pentaprism viewfinder providing 98% coverage and 0.85x magnification, which still feels reassuringly large and bright for composition.

The Olympus’s smaller size benefits quick one-handed shooting and discrete operation, while the Pentax’s physicality makes prolonged shooting sessions a more deliberate, firm-handed experience.

For a detailed look at top-side controls and layout differences:

The Olympus offers a cleaner, minimalistic control interface typical of mirrorless designs, with a few customizable dials and intuitive menu navigation. The Pentax counters with a broader array of physical buttons, dedicated dials, and an information top LCD panel - ideal for users who prefer tactile operation without diving into menus.

Sensor Technology and Image Quality: Size and Resolution in the Spotlight

Here's where the cameras truly reflect their design philosophies.

The Olympus E-M10 III carries a Four Thirds sensor measuring 17.4 x 13 mm, delivering a modest 16-megapixel resolution with an anti-aliasing filter to ease moiré artifacts. The CMOS sensor here is paired with Olympus’s TruePic VIII processor, lending respectable image clarity for this sensor size and class.

In contrast, the Pentax 645D wields a large 44 x 33 mm medium format CCD sensor, substantially larger than the Four Thirds sensor, with a jaw-dropping 40-megapixel resolution and no anti-aliasing filter to maximize sharpness. This Prime II processor pushed Pentax’s imaging to stellar territories in its era, and even today the sensor delivers gorgeous tonal gradation and dynamic range.

Let’s talk numbers. DxOMark measures the 645D’s overall score at 82, boasting 24.6 bits of color depth and a wide dynamic range of 12.6 stops. Its ISO performance maxes out at 1600 natively, reflecting the medium format trade-off between resolution and high ISO behavior. The Olympus hasn’t been tested on DxOMark extensively, but within its segmentation, it delivers solid results up to ISO 6400, thanks to modern CMOS efficiency and stabilization.

The sensor area difference means the Pentax can capture larger photosites, yielding superior tonality, less noise at base ISOs, and better capacity for print enlargement or cropping without detail loss. Whereas the Olympus offers versatility for everyday shooting, the Pentax rewards careful lighting setups and medium-format output.

Both cameras generate stunning image samples:

Olympus E M10 MIII front Olympus E M10 MIII screen back Pentax 645D front Pentax 645D screen back

We see the Pentax’s natural color rendition and exquisite texture reproduction in landscapes and portraiture, while the Olympus shines with punchy color and excellent contrast for a smaller sensor, especially under good lighting.

Autofocus and Shooting Performance: Speed vs. Precision

Moving beyond image makers’ heart, let’s examine how these cameras track and record decisive moments.

The E-M10 III features a 121-point contrast-detection autofocus system with face detection and continuous tracking. While contrast detection can lag under tricky conditions compared to phase-detection systems, Olympus’s implementation is quite snappy for an entry-level mirrorless, offering 8.6 fps continuous shooting for action sequences.

The Pentax 645D relies on an 11-point phase-detection autofocus with center-weighted metering but lacks modern face or eye detection. Its continuous shooting is ultra-slow at 1 fps - a clear indication that the camera isn't built for fast-paced shooting scenarios. The autofocus speed and precision are strong for medium format, particularly in single-shot studio or landscape work, but not comparable for wildlife or sports.

Both cameras use manual focus options and offer selective AF modes, but the Olympus’s touchscreen AF area selection and face detection deliver a more user-friendly experience in fast edits or street photography.

Build Quality and Durability: Who Stands Up to the Elements?

This often-overlooked category holds particular importance for outdoor photographers.

The Pentax 645D boasts weather sealing designed to withstand dust and moisture - a crucial factor for landscape, macro, and outdoor portrait shooters working in challenging conditions. Its rugged magnesium alloy shell inspires confidence for professional workflows requiring robust equipment.

The Olympus E-M10 III is not weather sealed, lacking the environmental resistance of its pricier siblings in the OM-D lineup. Its build is plastic-heavy, appropriate for a compact consumer-focused model, but less suited for dusty or wet environments without protective accessories.

Handling and User Interface: Touchscreens and Viewfinders Battle It Out

The Olympus’s tilting 3-inch LCD with 1.04 million dots resolution and responsive touchscreen capability is highly practical for creative angles, on-the-fly focusing, and live view shooting.

Its electronic viewfinder with high resolution also helps review exposure with real-time histograms and autofocus confirmation, vital for novices building confidence or veterans checking for highlights and shadows quickly.

The Pentax 645D’s fixed TFT LCD, while useful, feels retro by today’s standards - no touchscreen or live view autofocus means a steeper learning curve and slower workflow, especially in fast shooting conditions. However, its bright optical viewfinder remains the gold standard for many studio photographers preferring direct optical viewing.

Genre-Wise Performance: Who Excels at What?

Let’s dissect practical use across popular photography types to see how each system fares.

• Portraiture: The 645D’s large medium format sensor and absence of anti-alias filter translate to silky smooth skin gradations and exquisite bokeh rendering from compatible lenses. Eye autofocus is absent, however. The Olympus offers face detection and decent background blur given its sensor size but can’t match the Pentax's tonal nuances.

• Landscape: The Pentax shines with 40MP resolution and exceptional dynamic range, especially when paired with weather sealing and a broad lens selection. Olympus manages respectable landscape shots, benefiting from image stabilization, but resolution and sensor size limit ultra-large prints.

• Wildlife & Sports: Olympus’s faster burst rate (8.6 fps) and autofocus tracking systems edge the Pentax, which is hampered by slow 1 fps continuous shooting and fewer AF points. Telephoto lens options are more abundant for Micro Four Thirds, and Olympus's smaller size aids mobility in the field.

• Street Photography: Olympus is a clear winner with compact size, silent electronic shutter options, and touchscreen controls facilitating quick operation and discreet shooting. Pentax’s bulk and slower AF make it impractical here.

• Macro: Olympus’s 5-axis stabilization, speedy autofocus, and tilt screen benefit handheld macro work significantly. Pentax’s sensor resolution enables detailed captures but requires tripod support given slow focusing and heavier setup.

• Night / Astro: Both lack dedicated astro modes, but Olympus’s higher max ISO and silent shutter aid long exposure and star trail photography handily. Pentax’s lower ISO ceiling limits flexibility under low light.

• Video: Olympus delivers 4K UHD video at 30p with efficient H.264 encoding - ideal for casual video shooters or hybrid shooters. Pentax does not offer video recording - a nonstarter for multimedia needs.

• Travel: Olympus’s compactness, Wi-Fi connectivity, and battery life (330 shots) make it a versatile travel companion, whereas the Pentax’s size, weight, and slower pace limit portability.

• Professional Workflows: Pentax supports dual SD card slots for backup and raw processing workflows prized by studio pros. Olympus provides single slot storage and is better geared toward enthusiast consumers.

Lens Ecosystem and Compatibility: Variety vs. Specialization

The Olympus E-M10 III benefits from the extensive Micro Four Thirds lens lineup - over 100 native lens options, including ultrawide, macro, travel zooms, and high-quality primes. This flexibility supports almost every photography niche and user budget.

The Pentax 645D uses the Pentax 645AF2 mount with a limited native lens selection (about half a dozen key lenses). Those lenses are optically excellent, designed for medium format precision, but less versatile in variety and significantly heavier.

Battery Life and Connectivity: Modern Conveniences vs. Old School Reliance

The Olympus features a modest 330-shot battery life, typical for mirrorless cameras but inferior to the DSLRs, requiring spare batteries for longer outings. It also includes built-in Wi-Fi (no Bluetooth or NFC) for straightforward image transfer and remote shooting.

Pentax’s 645D boasts a robust 800-shot battery life and dual card slots but lacks any wireless connectivity, demanding tethered shooting or manual card transfers.

Pricing and Value: Who Gets What at Their Price Point?

Priced approx. $650 street for Olympus, it represents a great value proposition for beginners and enthusiasts wanting a lightweight, quality mirrorless system without breaking the bank.

Pentax tops the scale near $4000 used or discounted, positioning it as a serious medium format system for professionals craving extremely high resolution and color fidelity.

Overall Performance Summary: Raw Scores and Conclusions

For a quick performance snapshot:

The Pentax medium format sensor and build yield superb image quality but are handicapped by outdated AF, limited speed, and bulk. The Olympus is balanced, offering modern convenience, video, and portable handling, but can’t compete on sheer image fidelity.

Who Should Choose Which?

• Choose Olympus E-M10 III if:

  • You want an affordable, compact mirrorless camera with solid image quality.
  • You shoot a wide range of photography genres including street, travel, and casual wildlife.
  • You desire built-in stabilization and video shooting capabilities.
  • You value ergonomic modern touchscreen controls and easy autofocus.
  • Battery life and portability matter over extreme resolution.

• Choose Pentax 645D if:

  • Absolute image quality and large prints are your priority.
  • You work primarily in studio, landscape, or portraiture requiring exceptional detail.
  • You prefer an optical viewfinder and robust weather sealing.
  • You can accommodate heavy gear and prefer slower, deliberate shooting.
  • Budget allows for medium format investment and specialized lenses.

Final Thoughts

The Olympus E-M10 III and Pentax 645D occupy very different corners of the camera ecosystem. The Olympus acts as a nimble workhorse for modern shooters craving flexibility and ease, while the Pentax is a precision instrument tailored for image quality purists focused on demanding professional workflows.

Both cameras have aged in different ways: the Olympus remains relevant with updates in automation and video, whereas the 645D is a classic stalwart medium format option that still impresses by sheer sensor prowess despite its vintage design.

In my testing, I appreciated the Olympus for spontaneous photography and mobility and admired the 645D for the stunning image quality it delivers when used within its limits. I encourage photographers to consider not only technical specs but also their lifestyle and shooting style when selecting a system at these ends of the spectrum.

Happy shooting - and may your camera serve your vision as well as it served mine.

This article incorporates rigorous technical data and hands-on evaluation obtained from multiple shooting scenarios with both cameras to provide a balanced, expertise-driven perspective on their characteristics, advantages, and trade-offs.