IRIS Button on BMCC MFT

Sorry if that was answered before, but I simply can not find an answer online 
What does the Iris-Button on the BMCC MFT do? I heard it should enable and disable the Zebra, but it doesn't. Has it any function?
Best Regards

What does the Iris-Button on the BMCC MFT do? I heard it should enable and disable the Zebra, but it doesn't. Has it any function?
Best Regards