If the distance travelled by the light is reduced, then the image obtained from the experiment will be too dark to make any substantial observation regarding the objective of the experiment i.e. to measure the speed of the light. The apparatus kept at large distance allows the viewer to see the flickering of the light clearly as the image formed by the reduced intensity of the light enables a moderately clear view. Although in case the distance is decreased to 8.6 m, the intensity of the light will be too high to allow for a clear sharp view from the telescope.