I had an opportunity to look at a seasoned seamstress's work up close, and snapped a few pictures of the tiniest hem stitches that I have ever seen. They were almost invisible! Here are some close-ups:
This is what the back of the hem looks like. There are basting stitches here as well as the hem stitches. I hope to figure out how to do these tiny stitches so my hems can look this good!