I was not impressed with "Understanding Exposure", it contained far too many errors and inaccuracies among other things.
The funniest part was where he mentioned how to see depth of field on a camera without dof preview by pressing the lens release button and turning the lens 1/4 turn. This may have worked 20 years ago before Canon and others went to electronically controlled aperture!
Take a look at Alain Briot's "Mastering Landscape Photography", it is a very good photography book. You can try it before you buy it, some of the chapters are on The Luminous Landscape website.