Source 4 and iris - NEWBIE question

What do you use an iris for in a source 4 ellipsoidal? Is it to change the focus pattern (ie. shutters) or is it to limit the amount of fc's without changing the colortemp? Or none of the above. Thanks in advance.

 

An iris changes the beam size. Just like if you make a circle with your fingers and slowly make it smaller it would let less light through. It will make the beam smaller in the air and on the floor or wall where the light hits. So if you want a tight special on a persons face you could iris it down to there face. it also keeps the circle shape of the beam.

JH