Photography class students

According to the law of convex lens imaging, when u > 2f, it becomes an inverted and reduced real image. The photographer found that some students were not in the viewfinder, so the camera should be kept away from the students, which increased the object distance, and at the same time, the lens retracted and reduced the image distance. Only in this way can he get a clear image on the negative.

So, the answer is: far; Retreat.