Hello, I would like to invest on a new lens for spotting. I'm confused between Canon 70-200 F4L ii IS or Tamron 70-200 F2.8 VC G2. I'm wondering if F2.8 is really necessary for night photography, but at the same time I rarely did a night spotting. And for years I would like to own a Canon L lens, anyone can help me make my decision of saying which is the better choice and why? Thanks