Auto focus performance is excellent on both cameras. It does the job fairly quickly in daylight and slows down in dim light, but both cameras were still able to focus in most occasions, with or without the AF assist lamp.
One detail might be very useful for many users and I have to mention it: there is an option to automatically magnify AF point area after auto focus lock. That way you can monitor AF accuracy before taking a shot (images below).
Both cameras have small pop-up flash units, but G15 provides a standard hot-shoe for external flash which can turn this camera in a serious piece of gear.
OUT IN THE STREET
I took same shots with both cameras to see how they compare. As you can see, the result is almost identical (please evaluate only observing full-res images, not these thumbnails). The left column is Canon G15, right S110.
High ISO samples of the image at left can be downloaded as follows:
Personally, I would choose the G15. It’s easier to handle due to more external controls and dials, has brighter lens and the ability to extend battery life up to 600 shots using OVF. If you seek multi-purpose compact this one is to be considered closely. It should satisfy all your needs whether this would your only camera or a secondary one used when DSLR is simply too big and heavy to carry around. Excellent sensor and fast lens make an excellent pair and I can’t imagine anyone to be disappointed with image quality.
Canon Powershot S110 delivers basically the same image quality, but is too small for regular daily use in my opinion. The lens has a slower aperture at telephoto and limits the camera in low light. On the other hand, if you seek smallest available camera that can be carried anywhere and still have above average image quality and a nice set of features like RAW mode, customizable dials, touch LCD or Wi-Fi, then S110 might be the one to have.
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