i am very satisfied with the quality of pictures, especially if they are at ISO 100.
p510 performs well in daylight. at night, i have to use 'SCENE-portrait' mode or 'NIGHTLANDSCAPE' mode, both on burst-shot on in order to capture faces and moving shots. 'MANUAL' mode is good for non-moving subjects/tripod at night, otherwise too much blur occurs, forcing me to switch to SCENE-portrait or NIGHTLANDSCAPE mode. if even that fails to capture the subject due to low light and blur, what I do is take 1080p video, and pick still frames from the video. clear low-light pictures, although this results in a lower resolution image.
what annoys me about the p510 is its slow focus response. the subject would have already moved before i could even focus. and when shooting a video, the camera keeps on refocusing, especially when the subject keeps on moving.
if you are after zoom shots of relatively still subjects/objects, then the p510 is for you. it could even take an image of planets saturn and jupiter with its moons! for moving subjects, as long as they are well-lighted or in daylight, zoom shots are perfect.
before i forget, buy extra batteries (one or two extras).
i have not tried the canon sx40.
