focal length and aspherical lenses

[Robatman]

It seems like a worthwhile task, put an asph lens in and bam!! instant thrower (for example see http://candlepowerforums.com/vb/showthread.php?t=162189 )

Is there a way to measure the most appropriate focal length for a given light?? ie distance of emitter to lense?

Does having a shorter FL increase flood? lots of questions but at only $8 a pop may be worthwhile (suplusshed.com)


Thanks
Robert