Watch the Diminished online guitar lesson by Richard Hallebeek from Scale Creativity Guidebook
The diminished scale might be confusing to some, but if you use 3 note per string forms, then it’s actually quite clear to see across the neck. Also, you don't have to learn different scales, you can move the diminished scale up a minor 3rd to get to the next scale. If you start connecting these scales that are a minor 3rd apart, you'll get some really cool sounds.
There are three different types of diminished scales:
1. A form with all the notes a minor third apart from each other
2. The half-whole diminished scale – starts out with a half step, then a whole step
3. The Whole-half diminished scale – starts out with a whole step, then a half step.
The good thing is that the shapes you find in the scale are the same for the G and high E string and the same for the D and B string.