What should Xiaohong and other students do when taking a bust portrait with a camera while exploring the imaging rules of convex lenses?

Let me help you:

The original question should be: After taking a full body photo of Xiao Hong, what should I do if I want to take a half-length photo of Xiao Hong? Right

The specific operation is for the photographer to get close to Xiaohong and at the same time extend the camera lens forward. This will create a clear bust.

Because the half-body phase is larger than the whole body phase. Because the sizes of the negatives are the same, the half body is larger and the whole body is smaller.

According to the law of convex lens imaging, it can be seen that "the image of a near object becomes larger when it is far away", that is to say, if you want to make the image larger, you should make the object closer. When the object is closer, Finally, the image distance of the clear image is farther than before. In order to get a clear image, the distance between the lens and the film should be increased. The position of the film cannot be moved, so in order to increase the image distance, the lens had to be extended forward.

I hope it can be helpful to you and wish you good progress in your studies!