《小説（しょうせつ）》 なかなかお目（め）にかかれない美（うつく）しい景色（けしき）なので武（たけし）はここぞとばかりにカメラを手（て）にし、撮影（さつえい）した。
Novel: It's a beautiful scene that you don't see very often, so Takeshi took the opportunity to grab his camera and take some pictures.
ここ in this context means "now", as in "now is the moment I have been waiting/aiming for" and ぞ is used to emphasize determination. Therefore these expressions can be translated to "take advantage of the opportunity" or "grab the opportunity"