Tamron’s first
150-600mm lens was a pretty good buy at the price but the G2 (Generation 2) edition is better in every way. The optical path has been redesigned and now features three LD (Low Dispersion) elements rather than one. A new mix of coatings features both regular and nano-structure variants, and a fluorine coating is added to the front element. The G2 features more extensive weather-seals and better overall build quality.
An innovative new zoom lock mechanism enables you to lock the zoom ring. That can be a bonus for aircraft photography, where you might be pointing the lens directly upwards and want to avoid any zoom creep.