Sigma’s EM-140 DG ring flash builds in some of the features we’ve become used to with modern speedlights, like TTL and high-speed sync. Here’s my take on it.
The Yongnuo YN685 TTL flash works much the same as many other flashes, but there are some quirks to using it, especially wirelessly. Here are some tips.
There are a lot of videos on places like Youtube and Vimeo showing how to use off-camera flash, but some are definitely better than others. Gavin Hoey’s Fearless Flash Photography with Speedlights series is one of the best I’ve come across.