Sony 100-400mm f/4.5 GM: Constant Aperture Changes Everything

A constant f/4.5 across 100-400mm sounds like a spec sheet win, but the real story is what it does to your kit list. If this holds up in the field, it competes directly with Sony's 400mm f/2.8 GM and 100-300mm f/2.8 GM as a single-lens answer for wildlife and sports. That's two primes or a prime-plus-zoom combo potentially sitting out. For Sony shooters working action or wildlife, this review is the one to read before your next lens decision.