Focus Peaking is Not Perfect

It appears that focus peaking uses some sort of contrast detection methodology. While it is very useful and improves manual focus in digital cameras considerably compared to what other manual focus methods offer, it most definitely NOT perfect!

I've discovered that scenes where the edges between one object and another object are hard to see because the two objects are essentially the same color or reflect the same amount of light are difficult for focus peaking.

Try selecting your "best" OOF image sometime!

Another type of photo that I've discovered poses problems for focus peaking is situations where the areas you want to be out of focus also have areas of high contrast scattered about the scene. In this case, I've found that it isn't that focus peaking can't SEE the contrast, so much as it is that halos appear around the out of focus areas as well as the in focus areas, and the differences in the halos between the in-focus areas and the out of focus areas are so small that I can't tell exactly WHAT is in focus with any reliability.

I've learned not to fight with FP in situations where it doesn't do well. In both cases, I've found that switching to auto focus and selecting the appropriate focus point manually generally works well for me.