Many pro shooters flocked to the Olympus E-M5 as a more lithe companion to their DSLRs. A little over a year later, Olympus addressed some of the minor shortcomings of the E-M5 with the E-M1, a separate, pro-oriented model.
Let's get the simplest decision points out of the way: if you care about built-in Wi-Fi, the E-M1 is your ticket. Anyone with a library of old Four Thirds lenses will also fall in love with the E-M1 (it offers full compatibility with these lenses).
The E-M1 improves on the E-M5's strong AF performance by adding 37 on-sensor phase detect points. It's important to note, though, that phase detect is not available for video (and if you care about video, there are better options than either of these models).
Action photographers loved the E-M5's 4.2 frames per second shooting with continuous AF, but were stymied by the limited buffer depth of around 15 frames. The E-M1 boosts maximum shooting speed with continuous AF to 6fps, while offering a whopping 50 frames of buffer.
The E-M5 wowed us with intuitive and abundant manual controls. Olympus builds on this performance by adding numerous physical buttons -- most of them customizable -- while increasing their size and spacing (some complained of the E-M5's cramped layout). Two standout additions are a dedicated white balance button and Olympus's '2x2 Dial Control.' Read our review to learn more about these controls. The other major improvement is the larger electronic viewfinder, among the best we've seen.
Both cameras are truly great additions to the Micro Four Thirds family. There weren't any glaring weaknesses in the E-M5 to ameliorate, but all of the E-M1's additions are logical and welcome. Your decision will ultimately come down to whether the E-M1's additional features justify its size and price premium ($400 at time of writing) over the E-M5. Both are fantastic choices. You can purchase the E-M1 or the E-M5 through these links to help support our content.
Exceptional rugged, weather-proof, professional build; Lightning fast contrast-detect AF, and phase-detect AF that makes Four Thirds lenses far more responsive; Tons of useful physical controls with immense customizability; Arguably the best image quality of any Micro Four Thirds camera we've tested to date; Large, sharp, high-resolution electronic viewfinder; Advanced Wi-Fi capabilities, including remote control shooting in PASM exposure modes.
Bigger and heavier than many other compact system cameras; Most expensive Micro Four Thirds camera on the market to date; Menu system and customization options have a steep learning curve; No optical low-pass filter means greater risk of moire; No built-in flash.
Attractive body design; Well-built, weather-sealed body; Excellent image quality; Excellent image stabilization; Very fast autofocus.
Exposure compensation dial changes easily; Small buttons; No in-camera chromatic aberration correction; Bundled flash is weak; Video compression artifacts with rapidly-moving subjects.