During a recent TV commercial shoot our production had to film a hot-air-balloon against a blue sky so it could be used as part of a composite shot over the city of Paris. The basic idea was to film a static shot of the Eiffel Tower and then put a red-hot-air-balloon next to it in post. After several consultations with our post supervisor we decided the best and least expensive course of action was to film the balloon as a practical element.
Original text: French Balloon Ride