The SX150 is an incremental update to the SX130. Canon bumped up the image resolution to 14 megapixels with a 1/2.3 in sensor. Backing that up is the newer DIGIC 4 image processor, which brings several improvements to image processing and fixes to the continuous auto-focus.
Video mode is limited to 720 at 30 fps as it looks like Canon put most of the effort into the Smart Auto features on this model.
The SX150 offers RAW image storage and full manual control, not bad for a camera in the $250 range.
A smaller frame camera still packing a 12.1 megapixel 1/2.3 in sensor coupled with the DIGIC 4 processor. The 510HS supports 1080 HD at 24 fps or 720 at 30 fps and runs it all from a 3.2 touch panel LCD on the back.
There some interesting features, such as an option to take a picture by tapping the LCD screen, although I’m not entirely certain why you’d want to do that.
The 310 HS is a slightly scaled back version of the 510. It’s fitted with the same 12.1 megapixel sensor and the same DIGIC 4 image processor.
With the 310 HS you’re limited to an 8x zoom, a slightly smaller LCD screen and without the touch panel controls.
Interestingly the 310 HS also shoots 1080 HD at 24 fps, making the 310 and 510 the pocket cam choice for people using their full-size DSLRs primarily for video.
If you’re like most photographers and don’t understand why 24 fps is better than 30 fps for video, stayed tuned to this site for an extended post on DSLRs for video in the near future.