What is a trial judge's duty to instruct on lesser included offenses?

"'[A] trial court must instruct on lesser included offenses, even in the absence of a request, whenever there is substantial evidence raising a question as to whether all of the elements of the charged offense are present.' [Citation.] Conversely, even on request, a trial judge has no duty to instruct on any lesser offense unless there is substantial evidence to support such instruction. [Citation.] '"Substantial evidence is evidence sufficient to 'deserve consideration by the jury,' that is, evidence that a reasonable jury could find persuasive.'" (People v. Cunningham (2001) 25 Cal.4th 926, 1008.)