The OM-D E-M5's image performance is, in a word: Astounding. Image clarity has been increased from the E-P3, from approx. 1800 LPH (vertical and horizontal) to approx. 2200 LPH (vertical and horizontal). Noise performance has improved by unbelievable leaps and bounds, so unbelievable that it's redefined our beliefs about what a Micro Four Thirds (MFT) sensor can achieve. Images come with the famous Olympus colors, which make images look rich and seem to add additional depth to the greens and blues.
Now, to properly qualify that: This is still a MFT sensor. The image detail at lower ISO settings still doesn't match the best of what we see in APS-C sensors. But at higher ISO settings Olympus has pulled off some serious magic; the E-M5 can shoot up to such high levels with minimal grain appearing that it gives some APS-C cameras a run for their money. It's amazing how much detail is retained and how little noise is seen at high ISO levels.
Shooting with the E-M5 is a pleasure. Besides the ability to shoot at higher ISO sensitivities with confidence, the E-M5's auto-focus is fast and accurate. Like the E-P3, the E-M5 can even focus on faces and pin-point eyes as focal points. AF performance drops when shooting fast subjects in low-light, a challenging environment for any mirrorless system camera's contrast detect AF system, but it is surprisingly good in low-light for most other situations. The E-M5 makes it easy to change AF points, while shooting in Multi-AF mode all you need to do to manually take over AF point selection is to press any of the directions on the d-pad. To go back to Multi-AF mode, direct the AF point out of the AF grid.
The E-M5 comes with new 5-axis image stabilization, a first such system for mirrorless system cameras. We tried shooting ten second exposures without a tripod, not hand-held, but balanced on the edge of the camera and its protruded OLED monitor on some steps. While we tried to press the camera down onto the floor and hold it steady, we knew we would unconsciously introduce some camera shake with our hands. Miraculously, we got more sharp images than we should have, and we credit it to the image stabilization system.
The E-M5 shoots up to a record high ISO setting of ISO25,600, the highest ever from a Micro Four Thirds sensor (the previous record was ISO12,800, held by the Olympus E-P3 and Panasonic GX1). Just how much image noise is acceptable can be subjective and dependent on the photographer's needs, but based on what we see, we'd be confident of shooting with the E-M5 up to ISO6400, even ISO8000-ISO10,000 if we're shooting for low-resolution use. Grain can hardly be seen up to ISO6400 when viewed normally, and color noise hardly appears until ISO16,000 and above. ISO12,800 to ISO25,600 are generally too noisy to be used.
What's interesting is that while Olympus has managed to keep a very tight and impressive lid on image noise at high ISO levels, it doesn't seem to have improved ISO performance much at lower ISO settings. If we pixel-peep, we see noise appearing from ISO800 onward, at ISO1600 detail smudging becomes more apparent (again, this is if we pixel-peep). In consequence, if we need absolutely clean images for large prints or publication, we'd cap shooting at ISO800 and below.
We've seen some banding appear in some very high ISO shots. They don't always appear, and not always at the same settings, for example, the shots below were shot at ISO16,000 and ISO10,000. This is something you can see when reviewing your images on the OLED monitor, so it's worth checking your high ISO shots.
At the risk of sounding like a broken record: the E-M5's high ISO performance is astounding. While we would have preferred to see even cleaner images at lower ISO settings from ISO800-ISO1600, the ability to shoot up to ISO3200-ISO6400 with such low noise showing is nothing short of remarkable for a Micro Four Thirds sensor. Olympus has really upped the game here.