Don't know. Wish it was reversible but I think this has something to do with the "Leica" thing--the Panny Leica 45/2.8 has the same style hood.You can shoot without, you may end up with a little flare if you're shooting into a light source. I wish it was reversable as well, I can't figure out why they made it square.
I feel sure it would flare without and I do like the protection. To say a hood separates the amateurs from the pros is silly. I shot commercial for a good while for furniture and textile industries and I guarantee you that flare was always a possbility. Guess I could have used my hands to shield while camera was on tripod LOLOL.
Diane