Depth of focus

Shallow focus:

Shallow focus is a function of a narrow depth of field and it implies that only one plane of the frame will remain sharp and clear (usually the foreground).  In contemporary cinema, shallow focus is often combined with deep space for artistic purposes or to demonstrate subjectivity.  It is typically a feature of the close-up. So this means the use of shallow focus used with a close-up could represent a deep thought. positive and negative or could also show uncertainty.