Final answer:
To tighten the framing in his shot, Oscar should zoom in on his subject and/or physically move closer to it. Additionally, using a larger aperture can blur the background, emphasizing the subject further.
Step-by-step explanation:
Oscar can fill the frame with his subject to make the scene appear bigger with less visible background by taking one or both of the following actions: first, he should zoom in on the subject using his camera's zoom feature or by changing to a lens with a longer focal length. This will reduce the amount of background in the shot, making the subject more prominent. Second, Oscar has the option to change his position and physically move closer to the subject, which will also help to eliminate distractions from the background without the need to adjust the lens. Furthermore, manipulating the aperture setting to create a larger aperture can result in a narrower depth of field, making the subject in focus while the background becomes more blurred, enhancing the 3D effect of the image.