This is a quick review of the Sigma 50-500mm OS HSM (Nikon mount) that I rented from my favorite rental house, LensRentals.com. I had the lens for 5 days, having time to take many, many photos with it. I rented the lens primarily for birding. I had hoped to rent the 150-500mm instead, as I don't have a need for anything short of 300mm. Maybe Sigma will make a 300-500 f/5.6, or even an f/4. PLEASE!