Has anyone seen a lesson posted here that demonstrates how changing the f-stop/aperature affects the depth of field?

I told a friend I would send him a lesson (i.e. -- an excercise that he could do) so he could learn about f-stops.

I could probably design one easily/quickly, but I figured, "Surely such a valuable thing for novices already exists on photographyreview.com."

Plus, I'm lazy.

Plus, if I find the lesson here and send him the link, he will visit this web site, meet cool people and learn a ton!

Anybody seen such a lesson here?