Cutting part of an image to control opacity

I have a magnifying glass - I need to be able to lower the opacity of JUST the glass (so I can more clearly see what will be underneath), without affecting the opacity of the handle.  I thought they would need to be 2 separate items to do this. I would also be happy if i could select the glass alone, and lower the opacity - is that even possible?

Started in InDesign, and somehow managed to remove the glass - but couldn't find any way to "keep" the handle as well (see upload: "InDesign workings" where the glass is separate on left, but handle still has glass inside). You seem to only be able to keep what's INSIDE a shape. Not the inverse?

So I moved over to Illustrator, and made a mask - thinking I could cut the glass out, and move it aside so that I would have two pieces - handle and glass ("Illustrator workings" upload shows original magnifying glass (upper left), magnifying glass with mask on top (middle), and the mask on it's own (lower right). 

Please can some clever person tell me how I can separate the glass from the handle so as to be able to use them independently?  Is Illustrator the best app to use for this?

I feel like it should be so easy so I'm feeling pretty stupid right now! 

Many thanks!