Answer
Moving closer to the subject decreases the object distance.
Work Step by Step
The focal length of the lens stays constant. Equation 23-8, $\frac{1}{d_{o}} + \frac{1}{d_{i}} = \frac{1}{f}$, tells us that if $ d_{o}$ decreases and f stays the same, the image distance $d_{i}$ must increase. The camera lens moves farther away from the sensor.
