Depth of Field: The pictures above change the aperture setting of the camera lenses, creating a sense of depth in their images. The larger the apertures (smaller F-stop number) and closer the focusing distances, the shallower depth of field is. Other example of Shallow Depth of Field: http://digital-photography-school.com/17-beautiful-images-with-shallow-depth-of-field
Autumn tree: I like the angle of this shot because it enhances the trees large size. Additionally I like the shallow depth of field, focussing the lower leaf yet enhancing its colour with the out of focus background.