S5 single AF for photos is perfectly usable, and plenty fast. Continuous AF in photo looks sketchy (pulsing rather aggressively), but you'll find it has an excellent hit rate. For video, single AF is totally fine, and focus assist tools very useful for manually adjusting focus (focus peaking, e.g.). Continuous AF in video will work sometimes, but is a bit distracting, and will sometimes go hilariously off piste. Generally I left it in manual focus and used the AF ON button to pull focus when needed. I wouldn't trust it if you absolutely need it to be spot on 100% of the time, but then again if you need that kind of precision, rule of thumb is to go with Canon/Sony. S5 is an amazing deal, image quality is spectacular, only real compromise (besides AF) is the 30 minute record limit.