Performance and Image Quality
Improved auto focus speed, especially in low light, is one of the key benefits promised of the RX100 II's more sensitive backside illuminated sensor. Auto focus feels fast for a compact, nearing the best mirrorless cameras in terms of sheer speed. Sony boasts a top AF speed of 0.13 seconds, and field testing in the best of conditions give us no reason to doubt that number.
AF acquisition at wide angle slows a little in low light, but not by much. This is another area in which the RX100 II reveals its true sensor size; most modern compact cameras acquire focus quickly in good light but slow down significantly in low light. The RX100 II doesn't exhibit a dramatic decline in focus speed in less-than-ideal conditions - it shows the Sony habit of sometimes reverting to wide-area focus, rather than the chose point, but it's quick to make that decision, so you're not left waiting. At the telephoto end of the zoom, focus slows down by just a hair.
There are single, multi and continuous auto focus modes alongside manual (with optional focus peaking). The continuous focus mode can be somewhat jarring to use since it pulsates slightly when the shutter is half-pressed. That's a by-product of this contrast-based AF system making sure its subject hasn't moved, so a green icon on the bottom left corner of the screen indicates to indicate focus. A green dot appears between the parentheses when the subject's in focus, and disappears when the camera is seeking focus again.
It's generally reliable, though at close working distances the system occasionally had problems staying locked on a static subject. Using continuous AF with the lens zoomed to its full telephoto length was even more jarring, and produced slightly less than sharp images. The mode may be useful for objects at close range, but may be best avoided at the long end of the zoom.
Testing the RX100 II side-by-side with the RX100 didn't show the newer model to be decisively faster. It was at times, in good light, a hair faster than its predecessor, but not consistently. In low light they seemed to be evenly matched.
Overall the RX100 II is very fast for a camera of its size. You can certainly get faster cameras for its price, and an entry-level DSLR may still beat the RX100 II in terms of speed if you consider all shooting conditions. As it is, this is one of the fastest compacts we've used.
Continuous Shooting and Buffering
The RX100 II offers 10 fps speed priority and 2.5 fps standard continuous shooting modes. In the faster mode, the LCD shows the last frame captured, though focus and exposure are locked from the first frame. In the slower mode, setting continuous AF will allow the camera to reacquire focus between shots. Shooting JPEG only at the faster frame rate yielded about 14 frames with a 8GB UHS-I SanDisk SDHC memory card, with a brief pause once the buffer's full before it continues shooting at about 2 fps. After long bursts of shooting, releasing the shutter will produce a black screen while images write to the card, preventing any more shooting til it's done. At most, it lasted two or three seconds with the UHS card.
Speed priority mode in Raw + JPEG shooting produced a much slower rate of about 5 fps, yielding 10 frames before the buffer fills and a much longer write time to the card - around ten seconds (with the UHS-I card).
Image Quality (JPEG)
The Sony RX100 delivered some of the best image quality we've seen from a compact camera, and the RX100 II only promises improvements on that foundation. True to form, the RX100 II's JPEG images are highly detailed and generally well exposed with punchy color rendition.
Low light performance is one of the RX100 II's key selling points over its predecessor. The 20 megapixel CMOS sensor at the heart of the RX100 II is backside illuminated, meaning it's potentially more effective at collecting light. It was already pretty good to begin with, helped by a sensor 2.7 times larger than most of the rest of the class.
Shooting at f/1.8 is only available at the RX100 II's widest angle. From there, maximum aperture drops significantly as focal length is increased. The table below shows at which focal lengths the maximum aperture changes. In low light especially, 'zooming with your feet' when possible and keeping the aperture at its widest is a good idea.
The quick drop in maximum aperture is something we criticized the RX100 for making the camera's claim to a fast lens only true at wide angle. The RX100 II's BSI sensor shores up the loss just a little - though maximum aperture is still limited, less noise at higher ISOs potentially means faster shutter speeds can be used without sacrificing quite as much fine detail. However, that slow maximum aperture at the long end of the lens will tend to blunt some of the RX100 II's big sensor advantage, compared with its peers.
It's also worth noting that the RX100 II's maximum shutter speed is 1/2000sec and there's no neutral density filter in the lens, so you might find that the very widest aperture settings aren't practical to use in bright daylight. The filter adapter accessory for the RX100 II would remedy that problem (for an extra $30 for the adapter plus the cost of the filter).
If there's a complaint to be made about the camera's JPEG shooting experience, it's that the abundance of dynamic range and low light shooting modes can be slightly confusing. Handheld twilight, anti-motion blur, high sensitivity, night scene and night portrait are all available scene modes for when light is scarce. Some are unique in that they are multi-shot affairs, like handheld twilight, but some seem redundant. They may be confusing at first, but Sony's multi-shot modes are smart about picking the least-blurry frames and intelligent Auto mode will do a good job of selecting the right mode for you.
Sony promised better low light performance, and it has indeed been delivered. Is it $150 better? That's harder to work out. As it stands, it's hard to find faults with the RX100 II's image quality as compared to the rest of the compact class. Images at ISO 3200 are within the realm of usability, sharpness is excellent and the fast maximum aperture of the RX100 II's at wide angle is very useful in low light. However, it doesn't match up with a bigger sensor camera in terms of depth of field control and high ISO performance. As good as it is, the RX100 II is still (mostly) a compact camera.
The RX100 II is equipped with a built-in flash unit. Automatic flash can be used in Intelligent Auto, Superior Auto and Portrait and Macro scene modes, and fill flash is available in manual and semi-manual modes. At wide angle with auto ISO, the flash offers a working distance of 0.30 to 15 meters.